Search the FAQ Archives

3 - A - B - C - D - E - F - G - H - I - J - K - L - M
N - O - P - Q - R - S - T - U - V - W - X - Y - Z - Internet FAQ Archives

[l/m 9/30/2009] Water filters & Giardia Distilled Wisdom (9/28) XYZ

( Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Part8 - Part9 - Part10 - Part11 - Part12 - Part13 - Part14 - Part15 - Part16 - Part17 - Part18 - Part19 - Part20 - Part21 - Part22 - Part23 - Part24 - Part25 - Part26 - Part27 - Part28 )
[ Usenet FAQs | Web FAQs | Documents | RFC Index | Forum archive ]
Panel 9

See reader questions & answers on this topic! - Help others by sharing your knowledge
	a. Backcountry Drinking
	   [Comparison of filters, boiling and iodine]
	   Alan Dove, Bill Tuthill
	   Filters: First Need, Katadyn, MSR, PUR
	   Boiling, Iodine: PolarPure, Potable-Aqua 
	b. GIARDIASIS Memo from Center from Disease Control, 1990 memo
	   by Dennis D. Juranek replaced with URL link to the CDC
	c. Other research articles on giardiasis and cryptosporidiosis
	d. FDA Web pointer 
	e. REI Water Filter Chart
	   Comparison of specs: cost, pore size, field cleaning, weight,
	    pump force, output speed, etc.
	f. review of Katadyn Minifilter
	   Alan Malkiel 
	g. Misc.

TABLE OF CONTENTS of this chain:

9/ Water Filter wisdom					<* THIS PANEL *> 
10/ Volunteer Work 
11/ Snake bite 
12/ Netiquette 
13/ Questions on conditions and travel 
14/ Dedication to Aldo Leopold 
15/ Leopold's lot. 
16/ Morbid backcountry/memorial 
17/ Information about bears 
18/ Poison ivy, frequently ask, under question 
19/ Lyme disease, frequently ask, under question 
20/ "Telling questions" backcountry Turing test 
21/ AMS 
22/ Babies and Kids
23/ A bit of song (like camp songs) 
24/ What is natural? 
25/ A romantic notion of high-tech employment 
26/ Other news groups of related interest, networking 
27/ Films/cinema references 
28/ References (written) 
2/ Ethics 
3/ Learning I 
4/ learning II (lists, "Ten Essentials," Chouinard comments) 
5/ Summary of past topics 
6/ Non-wisdom: fire-arms topic circular discussion 
7/ Phone / address lists 
8/ Fletcher's Law of Inverse Appreciation / Rachel Carson / Foreman and Hayduke

# --enm: At this time, there is a report of a giardia "vaccine" in test,
# but no word on methods.  No vaccine reported by CDC to July 2009.

At this time (bordering on technically being War), there is no clarity
that any of the methods cited on this panel are 100% foolproof for
removing or destroying biological agents or any kind (lethal or
incapacitating) from a drinking water source.  This panel should not
be cited (excepting the CDC report).  Instead contact your local
Public Health Service officials.  Bring sources of contaminated water
to their attention.

From: "Jerry M. Wright" <>
To: "Eugene Miya" <>
Subject: Giardia panel
Date: Wed, 7 Mar 2001 21:10:51 -0500
Message-ID: <>
Importance: Normal

Here's an interesting recent publication.  Don't know if it's in the panel
but should be.

Risk of giardiasis from consumption of wilderness water in North America: a
systematic review of epidemiologic data.
AUTHOR AFFILIATION:  Department of Tropical Medicine, Tulane University
School of Public Health and Tropical Medicine, New Orleans, LA 70112, USA.
SOURCE:  Int J Infect Dis 2000;4(2):100-3

... Published reports of confirmed giardiasis among outdoor recreationalists
clearly demonstrate a high incidence among this population. However, the
evidence for an association between drinking backcountry water and acquiring
giardiasis is minimal. Education efforts aimed at outdoor recreationalists
should place more emphasis on handwashing than on water purification ...

Backcountry Water Drinking

 --Why Not Just Drink the Water?

In the Great Outdoors, there are potentially four dangers of
drinking water straight from a source (assuming it's freshwater,
# -- enm: it's actually more than 4, but this list is fine):
	chemical pollutants,
	protozoa and larger parasites,
	bacteria, and
In this panel, we will first discuss a few of the methods used
in the backcountry to avoid these dangers, then give a brief
description of the toxins and pathogens found in water, and which method
is best suited to neutralizing each. 

 --Methods of Purification
	The oldest (and cheapest) method of purifying water is to boil it. 
Boiling for five minutes will kill any biological hazards you could expect
to find.  Most pathogens are actually long dead by the time the water
boils, but the five minute boil will g et them all (remember to add 1
minute to this time for each 1,000 feet above 10,000 feet).  Boiling will
NOT neutralize chemical pollutants. 
	Chemical purification involves the use of iodine or chlorine to
kill the nasties in the water.  This method is lightweight and relatively
inexpensive, but will not neutralize chemical toxins.  In addition, you
must make sure that water at 25 deg. C (7 5deg. F) sits for 20-30 minutes
with iodine in it for purification to take place.  If the water is colder
(as it usually is), you will need to let it sit longer - possibly
overnight for cold stream water.  Warm the water against your body or even
on y our stove if you want it to be purified faster.  Once the appropriate
time has elapsed, the "band-aid" taste of iodine can be neutralized with a
small amount of ascorbic acid (vitamin C).  Used properly, iodine will
kill most protozoa and all bacteria and viruses in water.  After prolonged
use, some people develop thyroid problems, so be aware of this potential
side effect. 
	The latest rage in water purification is the use of filters, and a
large number of them are available (see the review later in this panel). 
There are a couple of things to bear in mind when shopping for filters. 
First, only a system which includes a n iodine matrix will kill viruses
(see below).  Second, a filter with pores larger than 0.2 microns - note
the location of the decimal point, as it is important - will let bacteria
through.  The advantages of a filter are quick processing time (don't have
to wait for the pot to boil or the iodine to do its work) and
clean-tasting water (no iodine or vitamin C flavor).  Some systems also
contain a carbon filter which will remove chemical toxins. 
	Finally, one system seldom used by hikers, but carried on seagoing
boats and possibly sea kayaks, is the reverse osmosis, or RO filter. 
These systems are bulky, heavy, and expensive, but they will desalinate
seawater - a useful thing to be able to do
 on a lifeboat, for example.  Such filters will also remove all biological
contaminants, including viruses (viruses are considerably larger than the
exclusion limit of the RO filter). 

--What Might Hurt You
	Chemicals in water could include inorganic contaminants (arsenic
and other heavy metals) or organic toxins (fertilizers and pesticides, for
example).  In general, it is a bad idea to trust any purification system
to remove these, as even small quantit ies could ruin your day in a hurry. 
The good news is that water sources in the backcountry are seldom
contaminated with appreciable levels of toxic chemicals.  Take a good look
at the stream you're about to get water from.  Are there fish in it?  Is
there algae on the rocks?  Crawdads on the bottom?  Insects skimming the
surface?  Plants growing along the banks?  If yes, the water is probably
non-toxic, chemically speaking.  If you're hiking in the desert, though,
and a trickle of water etching a groove in the rock is bubbling sulfur
from its barren depths, you should probably avoid it. 
	There are a number of parasites, both multicellular and
unicellular, which live in water.  The most common ones in North America
are _Giardia lamblia_ (see the CDC report later in this panel) and
_Cryptosporidium_.  A good filter will remove both, and
 boiling will kill them.  Iodine is a reasonable second choice, but is a
bit chancy in water carrying Crypto.  In third-world countries, the number
of parasites in the water is staggering, hence the hackneyed advice,
"Don't drink the water."  Amoebae can cause dysentery ("Montezuma's
Revenge"), whipworm causes diarrhea and possible complications if not
treated, and roundworms (_Ascaris lumbricoides_) can be unpleasant, to
name a few.  In some areas, such as the Philippines and Africa, you should
tr y to avoid ANY contact with river water, including swimming or washing
in unpurified water, as _Schistosoma_ sp. is prevalent in these areas. 
These tiny parasites bore directly into the skin, entering the bloodstream
and eventually setting up shop in
 either the intestine or the bladder.  If left untreated or incorrectly
diagnosed (a common problem, as symptoms only become manifest weeks or
months after contact), the complications can be severe.  As with
_Giardia_, though, all of these parasites ar e removed by filtration or
killed by boiling. 
	Bacteria are the second smallest pathogens in water, but they can
still be removed by a 0.2 micron filter.  One frequently hears about water
being tested for _Escherichia coli_.  While strains of this bacterium can
be pathogenic, the vast majority are
 not, and it is, in fact, one of the species required in the intestine for
digestion to occur (without bacteria, we would all die).  Since it is
present in large quantities in sewage, it is a good indicator strain to
show when water has been contamina ted with sludge.  There are plenty of
other bacteria which are happy in the intestine, to the detriment of the
host.  All are sensitive to iodine treatment, are killed by boiling, and
are removed by good filters. 
	The smallest parasites are viruses (please direct pointless
debates about whether or not they are "alive" to one of the
groups).  In true wilderness areas, pathogenic viruses are seldom found in
water, but the odds increase with population dens ity and poor sanitation
practices.  Ordinary filters DO NOT remove viruses - in fact, Louis
Pasteur originally defined viruses as "filterable agents," meaning they
traveled easily through a 0.2 micron ceramic filter.  Filters which have
an iodine matri x will kill viruses ("inactivate" them, if you prefer),
and iodine treatment will also work.  Boiling is the most reliable way to
do away with viruses, though, and is strongly suggested in third-world
countries.  The specific viruses you should worry about in water are
hepatitis A, rotaviruses, polioviruses, and echoviruses.  All of these
will cause diarrhea, intestinal cramps, and discomfort about 48-72 hours
after contact, and complications could range from liver damage (for
hepatitis) to aseptic
 meningitis and encephalitis (for echoviruses), and paralysis or death
(for polio).  Yes, everyone is vaccinated against polio these days, but if
you were born before the vaccine, you could have problems with it. 

--Notes About This Introduction

1) Boiling your water is cheap and easy, and kills all known pathogens. 
If you can manage the extra fuel necessary, this is the preferred method. 

2) In the United States, you will seldom encounter anything in drinking
water which can kill you (make you sick, yes, but probably not kill you). 
Be careful, but don't have a heart attack if you accidentally swallow some
unpurified stream water.  The c hances are thousands of times greater that
you will die in an automobile accident. 

3) Anecdotal evidence which you see on the Net should largely be ignored,
especially the "I've used X method for 20 years and never had a problem"
variety.  Since most water is not contaminated to begin with, just about
any method could appear to work for quite awhile. 

4) This introduction was written by Alan Dove and edited by Eugene Miya
[well, I studied biological warfare] and Bill Tuthill.  All three know the
subject matter, but this information is intended only for general
guidance.  Anything that happens to you as a result of following or not
following it is your own damned fault. 


OCR'ed memo from the Centers from Disease Control: 
GIARDIASIS: By Dennis D. Juranek, Chief, Epidemiology Activity Parasitic, 1990

A majority of the people involved in the experiment which OCR'ed
Dr. Juranek's memo in the early days before the web have agreed that it
would be better to remove his older memo and instead point to the CDC's
own web site's pages.  The experiment was tried to see how much effort
the r.b. community would attempt to work with existing sources of
external information.  Some of the results include the other parts of
this panel as well as parts of the Lyme and poison ivy/oak panels.
This panel continues to need work restructuring it.  But the original
contributors don't really have the time.

Please see select the 'G' letter in the Index
(currently top of the home page) and link "Giardia."  The web site has a
number of advantages including not only being more up to date but also
having images which are a little harder to Usenet to transmit.
Dr. Juranek himself has authored other memos and papers following 1990
and those are referenced on the CDC web page.  Use the CDC's information
which should be considered authoritative.

The original text was moved to the end of this panel and will be
completely removed at the end of 2009.

Temporary Patch:
        Tinidazole (Tendamax) is now available in the US
        both in trademarked and generic form.
	It is now apparently the usual treatment for Giardia.

This patch will also remain until end of 2009.



                             (Fact Sheet) 

What is cryptosporidiosis? 

Cryptosporidiosis is a disease caused by the parasite Cryptosporidium
parvum, which as late as 1976 was not known to cause disease in humans.
Until 1993, when over 400,000 people in Milwaukee, Wisconsin, became ill
with diarrhea after drinking water conta minated with the parasite, few
people had heard of either cryptosporidiosis or the single-celled
intestinal protozoon that causes it.

Since the Milwaukee outbreak, concern about the safety of drinking water
in the United States has increased, and new attention has been focused on
determining and reducing the risk for cryptosporidiosis from community and
municipal water supplies.

How is cryptosporidiosis spread? 

Cryptosporidiosis is spread by putting something in the mouth that has
been contaminated with the stool of an infected person or animal. In this
way, people swallow the Cryptosporidium parasite, which is too small to be
seen with the naked eye. A person c an become infected by drinking
contaminated water or eating raw or undercooked food contaminated with
Cryptosporidium oocysts (an egg-like form of the parasite that is the
infectious stage); direct contact with the droppings of infected animals
or stool o f infected humans; or hand-to-mouth transfer of oocysts from
surfaces that may have become contaminated with microscopic amounts of
stool from an infected person or animal.

What are the symptoms of cryptosporidiosis? 

Two to ten days after infection by the parasite, symptoms may appear.
Although some persons may not have symptoms, others have watery diarrhea,
headache, abdominal cramps, nausea, vomiting, and low-grade fever. These
symptoms may lead to weight loss and d ehydration.

In otherwise healthy persons, these symptoms usually last 1 to 2 weeks, at
which time the immune system is able to stop the infection. In persons
with suppressed immune systems, such as persons who have AIDS or recently
have had an organ or bone marrow tr ansplant, the infection may continue
and become life-threatening.

What should you do if you suspect that you have cryptosporidiosis? 

See your physician. Since the routine stool examination used for most
parasites usually fails to detect Cryptosporidium, a stool specimen should
be examined using stains/tests available especially for this parasite. It
is important for persons with a poor ly functioning immune system to seek
medical attention early in the course of their disease. 

 What is the treatment for cryptosporidiosis? 

No safe and effective cure is available for cryptosporidiosis. 

People who have normal immune systems improve without taking antibiotic or
antiparasitic medications. 

The treatment recommended for this diarrheal illness is to drink plenty of
fluids and to get extra rest. Physicians may prescribe medication to slow
the diarrhea during recovery. 

Who is at risk? 

Persons at increased risk for cryptosporidiosis include child care
workers; diaper-aged children who attend child care centers; persons
exposed to human feces by sexual contact; and caregivers who might come in
direct contact with feces while caring for a
 person infected with cryptosporidiosis at home or in a medical facility.
Once infected, persons with suppressed immune systems, such as cancer
chemotherapy patients, are at risk for severe disease. 

How can you prevent cryptosporidiosis? 

     Avoid water or food that may be contaminated.  Wash hands after using
the toilet and before handling food.  If you work in a child care center
where you change diapers, be sure to wash your hands thoroughly with
plenty of soap and warm
 water after every diaper change, even if you wear gloves. 

During communitywide outbreaks caused by contaminated drinking water, boil
drinking water for 1 minute to kill the Cryptosporidium parasite. Allow
water to cool before drinking it.

HIV-infected persons should avoid drinking water directly from lakes or
rivers; avoid unpasteurized milk or milk products; avoid exposure to
calves and lambs and places where these animals are raised; wash hands
after contact with pets; and wash hands aft er gardening or other contact
with soil. Because any sexual activity that brings a person in contact
with the feces of an infected partner greatly increases the risk for
cryptosporidiosis, HIV-infected persons and AIDS patients should follow
safer sex gui delines and avoid sexual practices that may result in
contact with feces.

If you are a caregiver of cryptosporidiosis patients, wash hands after
bathing patients, emptying bedpans, changing soiled linen, or otherwise
coming in contact with the stools of patients.

If you have cryptosporidiosis, wash your hands often to prevent spreading
the disease to other members of your household.

 For more information on cryptosporidiosis, see the following sources: 

Cordell RL, Addiss DG. Cryptosporidiosis in child care settings: a review
of the literature and recommendations for prevention and control. Pediatr
Infect Dis J. 1994;13(4):310-7.

Dubey JP, Speer CA, Fayer R. Cryptosporidiosis of man and animals. Boston:
CRC Press, 1990.

LeChevallier MW, Norton WD, Lee RG. Giardia and Cryptosporidium spp. in
filtered drinking water supplies. Appl Environ Microbiol

MacKenzie WR, Hoxie NJ, Proctor ME, Gradus MS, Blair KA, Peterson DE,
Kazmierczak JJ, Addiss DG, Fox KR, Rose JB, Davis JP. A massive outbreak
in Milwaukee of Cryptosporidium infection transmitted through the filtered
public water supply. N Engl J Med 199 4; 331:161-7.

Rose JB, Gerba CP, and Jakubowski W. Survey of potable water supplies for
Cryptosporidium and Giardia. Environmental Science and Technology

Smith PD, Quinn TC, Strober W, Janoff EN, Masur H. Gastrointestinal
infections in AIDS. Ann Intern Med 1992;116:63-77. 

                       Centers for Disease Control and Prevention National
Center for Infectious Diseases Division of Parasitic Diseases June 1995


Back-country water treatment to prevent giardiasis. Jerry E. Ongerth, PhD,
PE, Ron L. Johnson, Steven C Macdonald, MPH, Floyd Frost, PhD, and Henry
H. Stibbs, PhD

American Journal of Public Health December 1989, Vol 79, No 12, pp

Copyright 1989 AJPH 0090-0036/89$1.50 [used without permission]


This study was conducted to provide current information on the
effectiveness of water treatment chemicals and filters for control of
Giardia cysts in areas where treated water is not available.  Four filters
and seven chemical treatments were evaluated fo r both clear and turbid
water at 10C.  Three contact disinfection devices were also tested for
cyst inactivation.  Filters were tested with 1-liter volumes of water
seeded with 3x10^4 cysts of G. lamblia produced in gerbils inoculated with
in vitro cultur ed trophozoites; the entire volume of filtrate was
examined for cyst passage.  Chemical treatments were evaluated at
concentrations specified by the manufacturer and for contact times that
might be expected of hikers (30 minutes) and campers (eight hours,
 i.e., overnight).  Two of the four filter devices tested were 100 percent
effective for Giardia cyst removal.  Of the other two filters, one was 90
percent effective and the other considerably less effective.  Among the
seven disinfection treatments, the
 iodine-based chemicals were all significantly more effective than the
chlorine-based chemicals.  None of the chemical treatments achieved 99.9
percent cyst inactivation with only 30-minute contact.  After an
eight-hour contact each of the iodine but none
 of the chlorine preparations achieved at least 99.9 percent cyst
inactivation.  None of the contact disinfection devices provided
appreciable cyst inactivation.  Heating water to at least 70C for 10
minutes was an acceptable alternative treatment. 



Giardia lamblia is the most commonly identified human intestinal parasite
in the United States.  Giardiasis is commonly transmitted between humans,
especially among small children.  lt is also transmitted in water,
particularly in the mountainous regions of the U.S.  Since 1965, over 80
waterborne outbreaks of giardiasis have occurred in community water
systems, affecting more than 20,000 persons (1).  Giardiasis in hikers and
campers has also been documented (2,3); indeed, it is commonly considered
a bac kpackers' illness.  Giardia cysts in concentrations as high as four
per gallon have been detected in untreated surface water in northeastern
and western states (4). 

Concern over waterborne transmission of Giardia has led to development of
a variety of chemical disinfectants and portable filters for individual
use in the backcountry.  Although some information on such methods has
been reported (2,5,6), there is no com prehensive guide to their
reliability in actually removing or inactivating Giardia cysts.  We tested
four commercially available portable filters and one contact disinfection
device for their ability to remove Giardia cysts from water.  We also
evaluated the cysticidal effectiveness of seven chemical disinfectants and
three contact disinfection devices. 



Cysts of G. lamblia were prepared for use in both the filtration and
disinfection tests by propagation in gerbils inoculated with trophozoites
from sterile culture.  Trophozoites were of two isolates: one from a
beaver (Be-4 isolate from Alberta) and one from a human (H-2 CSU isolate
from Colorado).  Cysts were concentrated from crushed, filtered gerbil
feces by flotation on zinc sulfate (sp. gr. 1.18), cleaned, and stored in
distilled water at 4C for up to 10 days before use.  Similarly, G. muris
cysts o f an isolate originally obtained from hamsters (7) were purified
from feces of infected athymic (nu/nu) mice and stored before use.  Cyst
concentrations were determined with a Coulter Counter (Model ZBI, Coulter
Electronics, Hialeah, FL) and a haemacytome ter.  Except where noted,
cysts were added to water samples in concentrations of about 3x10^4/ml. 
Cyst viability was assayed by fluorogenic staining (8) and in vitro
excystation (7).  In the former method, live cysts are distinguished by
two fluorescing dyes.  One dye is fluorescein diacetate (FDA), which when
absorbed by cysts produces a fluorescent green only in live cysts; the
second dye, either propidium iodide (Pl) or ethidium bromide (EB), is
excluded efficiently by live cysts but absorbed by dead cysts, resulting
in red fluorescence. 

Filter testing

The following backpacker-type water filters were purchased from local
retailers: First Need Water Purification Device (First Need), General
Ecology Inc., Lionville, PA;
H2OK Portable Drinking Water Treatment Unit
Model No. 6 (H2OK), Better Living Laboratories Inc., Memphis, TN;
[potential errata: This firm maybe be defunct.  Awaiting confirmation.]
Pocket Filter (Katadyn), Katadyn Products Inc., Wallisellen, Switzerland;
and Pocket Purifier, Calco Ltd, Rosemont, IL.  Also noted in this category
is the Water Tech Water Purifier (Water Purifier), Water Technologies Corp
., Ann Arbor, Ml.  Although it is not advertised as a filter and was not
specifically tested for Giardia cyst removal, we report qualitative
observations made during disinfection testing (see below) because its
configuration and mode of operation suggest that particle removal may
occur.  Physical and operating information provided in the filter
packaging is summarized in Appendix A.  Each device was tested when it was
new.  Devices that removed all cysts when new were retested after a period
of use approx imating several months for a regular weekend user. 

Each filter was prepared for testing by filtering four liters of tap water
to purge loose carbon particles or debris.  The cyst removal performance
of each filter was determined by filtering one liter of spring water,
turbidity of 0.1 NTU, to which formal in-fixed G. lamblia cysts had been
added.  The entire filtrate volume was passed through a 25-mm dia., 5-um
pore size, polycarbonate membrane (Nuclepore, Pleasanton, CA),  stained
with EB (100 ug/ml), and mounted under a cover slip.  Cysts were counted
at x250 magnification with the aid of epifluorescence microscopy.  A
representative portion of each filter was examined to quantify cyst
recovery as described previously (9).  The area examined was inversely
proportional to the number of cysts found and ran ged from 3.5 percent of
seeded positive control filters to 25 percent (one quadrant) of filters
with cyst densities less than one per field.  Total numbers of cysts
present were estimated by extrapolation in direct proportion to the area
examined.  In ext ensive work on recovery of Giardia cysts using the
procedures described above, cyst retention on the 5-um polycarbonate
membrane in a single filtration step has routinely averaged 80 to 90
percent (Ongerth JE: unpublished).  Accordingly, the ability to id entify
high levels of cyst removal, which would result in passage of very few or
no cysts, is excellent.  This ability is unaffected by the factors that
contribute to lack of precision in counting large numbers of cysts on
filters; such inaccuracies usual ly occur when only small representative
subareas are examined and the total numbers are estimated by
extrapolation.  A seeded positive control and an unseeded negative control
were processed with each batch of filter evaluations.  The cyst removal
perform ance evaluation was replicated three times for each filter device,
with results expressed as the arithmetic average and corresponding
standard deviation. 

Contact Disinfection Testing

The Water Purifier is described in packaging information as a contact
disinfection device.  Likewise, the {H2OK and} Pocket Purifier devices are
described as providing disinfection as well as removing cysts by
filtration.  These devices were therefore teste d for their effect on cyst
viability in addition to filtration efficiency.  A single 500-ml sample
for each device was seeded with approximately 2.5 x 10^4 cysts and passed
through the device.  Filtrate was collected and filtered as described
above to rec over cysts.  The viability of cysts was then assessed by FDA
and EB staining as described below. 

Disinfectant Testing

The cysticidal effects of seven commercially available and commonly used
disinfectant preparations were tested with identical procedures.
Four of the products were iodine based:

	Polar Pure Water Disinfectant (Polar Pure),
	Polar Equipment, Saratoga, CA;

	Coghlan's Emergency Germicidal Drinking Water Tablets (CEGDWT).
	Coghlan's Ltd, Winnipeg. Canada;

	Potable Aqua Drinking Water Germicidal Tablets (Potable Aqua),
	Wisconsin Pharmacal Inc., Jackson, WI; and

	2 percent iodine prepared from I2 reagent grade
	(Baker, Phillipsburg, NJ).

The remaining three products were chlorine-based:

	Sierra Water Purifier (Sierra), 4 in 1 Water Co., Santa Fe, NM;

	Halazone, Abbott Laboratories, North Chicago, IL; and

	commercial liquid bleach (5.25 percent sodium hypochlorite).

Disinfectant solutions were characterized by pH and total halogen
concentration (Appendix B), the latter being determined colorimetrically
using the DPD method. 

Two water sources were used, one to reflect clear high-mountain
conditions, the other to reflect downstream, more turbid conditions. 
Water sources were characterized by pH, turbidity, and free chlorine
demand (Appendix C).  The upstream source was from
a small, spring-fed tributary to the Snoqualmie River near North Bend,
Washington.  Samples were taken from the stream approximately 50 yards
downstream from the spring.  The downstream source was the discharge from
Lake Washington in Seattle, Washington.
 Samples were taken in midstream at the entrance to Portage Bay, adjacent
to the University of Washington campus.  Water samples were prepared for
testing by adding disinfectant, according to manufacturers' instructions,
to one liter of water in stoppered
 glass bottles (Appendix B). 

Cysticidal properties of the chemical treatments were determined as follows:

1) Water was put in 50-ml disposable plastic centrifuge tubes and placed
in a 10C incubator. 

2) G. lamblia cysts were added to each test sample at time zero. 

3) Tubes were vortex-mixed, sampled, and returned to the incubator. 

4) At each sampling time, i.e., time 0, 30 minutes and 8 hours, a 10-ml
sample was withdrawn; a portion was used for measuring disinfectant
concentration, and in the remainder the disinfectant was quenched with
0.1-mM sodium thiosulphate. 

5) Cysts in the quenched sample portion were exposed to aqueous solutions
of the viability indicators, FDA (25 ug/ml) and EH (100 ug/ml), filtered
on to a 13-mm dia. 5-um pore-size filter membrane, and rinsed with
distilled water (10 ml). 

6) Filters were mounted on glass slides, sealed under coverslips and
examined by epifluorescence microscopy at x250 magnification (Model 16,
Carl Zeiss, Inc., Thornwood, NY) to enumerate proportions of red and green
fluorescing cysts indicating dead and l ive status, respectively.  The
viability baseline of the cysts was established by running a control
sample of untreated water seeded with cysts through each test, using
procedures identical to those for disinfectant- treated samples.  Data are
presented i n terms of percent survival relative to the controls (Figure 2).
The effectiveness of each disinfectant for killing cysts in both
upstream and downstream water was determined in triplicate, with results
expressed as the arithmetic average and correspondi ng standard deviation. 

The Water Tech Water Purifier, a contact disinfectant, was also tested as
a chemical disinfectant.  The test water was 100 ml of spring-source water
seeded with Giardia cysts.  The treated water was filtered, stained, and
examined for cyst viability as de scribed in steps 5 and 6 above.  Three
replicates were assayed. 

Heat Inactivation

Inactivation of G. lamblia and G. muris cysts by heating was established
as follows.  Cysts were added to distilled water in 15-ml glass test
tubes.  The seeded tubes were incubated for 10 minutes at temperatures
ranging from 10C to 70C.  Afterwards, cyst suspensions were cooled immediately
by swirling in 10C water for one minute.
Cyst viability was determined either by excystation or by staining.
If by the latter, FDA and EB were added to the samples, the
tubes were vortex-mixed, and a 1-ml aliquot was filtered through
a 13-mm dia. 5-um pore-size filter membrane.  Filters
were rinsed, mounted, and examined as described above to enumerate the
live and dead cysts. 



Filter Device Tests

The four filters differed significantly in their ability to remove Giardia
cysts (Figure 1).  The number of cysts recovered from water having passed
through the filter devices ranged from zero to greater than 10^4 in
individual tests.  The performance of individual devices was consistent as
indicated by the standard deviations for each of the three replicate test
sets (Figure 1).  The percentage of cysts removed by the devices,
corresponding to 100 minus the percent of cysts recovered from the
filtrate, w as 100 percent for the First Need and Katadyn filters and
approximately 90 percent for the {H2OK filter}.  The concentration of cysts
in the Pocket Purifier effluent was not statistically different from the
seed concentration. 

The First Need and Katadyn filters were then subjected to a period of
moderate use and then retested.  The volume of water processed during the
simulated use period was not the same for the two filters owing to
differences in their operation.  The differe nce in volume had no apparent
effect on performance of the two filters.  A total of 88 liters of tap
water (turbidity of 0.3 NTU) was filtered with the First Need.  During the
process it was back-flushed, as recommended in package instructions,
because th e filtration rate decreased after 50, 71, and 75 liters had
been filtered.  After 88 liters had been processed, the filtration rate
was about 25 percent lower than when the filter was new, and it was
retested in that condition.  The Katadyn filter was sub jected to use by
filtering one liter of tap water four times a day for five days.  At the
end of each day, the filter was cleaned according to package instructions
by disassembling, brushing the filter element, and allowing it to air-dry
overnight before reassembly.  After the respective periods of use, these
two filters were tested in triplicate for efficiency of cyst removal. 
Performance of these filters was the same, 100 percent cyst removal, when
they were retested. 

Cyst Inactivation

Contact Disinfection Devices - The effect of each of the contact
disinfection devices on G. lamblia cyst viability was limited.  The Water
Purifier inactivated about 15 percent of the cysts added in 100 ml of
upstream (low turbidity) water; {the H2OK filter inactivated about 5
percent of the cyst challenge,} and the Pocket Purifier inactivated about 2
percent of the cyst challenge. 

Chemical Disinfectants - The effectiveness of seven disinfecting chemical
preparations ranged from only a few percent to greater than 99.9 percent,
depending on the chemical and its concentration, the contact time, and the
disinfectant demand of the water (Figure 2).
None of the disinfectants was more than 90 percent effective
after a contact time of 30 minutes.  After eight-hour contact, the four
iodine-based disinfectants, each caused a greater than 99.9 percent
reduction in viable cysts.  The chlorine -based disinfectants were clearly
less effective than the iodine-based ones at both contact times. 

Heating in Water - Experiments conducted with cysts of G. lamblia and of
G. muris indicated that the two species have virtually the same
sensitivity to inactivation by heating.  Cysts at both species were
completely inactivated by heating to 70C for 10 mi nutes.  Heating to 50C
and 60C for 10 minutes produced 95 and 98 percent inactivation,
respectively (Figure 3). 



To remove Giardia cysts from water, one must use a filter with
sufficiently small pores to trap the cysts and sufficiently large capacity
to produce a useful volume of treated water before backwashing or
replacement is necessary.  Although a number of man ufacturers advertise
that their filters remove Giardia cysts, the only previously published
account of filter performance was for the Katadyn unit (6).  Our filter
evaluation study showed that only the First Need and the Katadyn filters
removed cysts with at least 99.9 percent effectiveness.
Under the same test conditions, {the H2OK filter was
approximately 90 percent} effective and the Pocket Purifier
was less than 50 percent effective for cyst removal.  The analysis of
viability for the cysts collected i n the effluent of the Water Purifier,
{H2OK,} and Pocket Purifier indicates that passage through the device did
not significantly reduce the percentage of viable cysts. 

The current study showed that none of the chemical treatments could
inactivate more than 90 percent of cysts with 30 minutes of contact time
at 10C.  At both 30 minutes and eight hours of contact time, the
iodine-based disinfectants inactivated a higher f raction of cysts than
did the chlorine-based products.  All methods inactivated a lower
percentage of cysts in cloudy or turbid water than in clear water.  All
disinfectants performed better with eight hours of contact time than with
30 minutes.  Only the iodine-based compounds
inactivated 99 to 99.9 percent of cysts, within eight hours of
contact time for both turbid and clear water.  As observed
by Jarroll, et al (5), the 2 percent tincture of iodine was less effective
than the other iodine preparations with 30 minutes of contact time,
but it was as effective as the others at eight hours.
Comparison of our results with those of Jarroll, et al (5),
is complicated by differences between test conditions used.  However, our
results generally indicate more stringent requirements for effective
inactivation of Giardia cysts.  Differences between cyst populations used
in the two studies could account for the observed differences, even though
both were G. lamblia.  Cysts produced in our trophozoite - gerbil sys tem
had consistently high intrinsic viability (>80 percent), excysted
efficiently when fresh (80 to 90 percent), and have appeared more
resistant to halogen disinfectants than reported previously (Ongerth J.E.:

The results of heat inactivation in our study correspond to previous
reports indicating that heating to between 60C and 70C kills Giardia cysts
efficiently.  In addition, our data illustrate the correspondence between
the fluorogenic staining and in vitro
 excystation procedures for assessing cyst viability.  When applied to
cysts of the same condition.  Staining indicates a slightly higher
proportion of viable cysts than does excystation.  Overall, however, the
two procedures provide comparable informatio n. 


Figure 1 - Effectiveness of Four Portable Water Filters for Removal of
Giardia Cysts from One-Liter Volumes of Water Each containing
approximately 3x10^4 Cysts (dotted line).  [A bar chart showing the
positive and negative controls and results from the fi lters, on a log
scale.  The First Need and Katadyn results and the negative control were
all zero.  The Pocket Purifier and the positive control were approximately
the same - i.e. the Pocket Purifier did not remove cysts at all.  {The H2OK
results were somewhat below the positive control, actually -- due to the
log scale -- indicating 90% removal.]}

Figure 2 - Effect of Time and Disinfectant Concentration of Seven Chemical
Disinfectants on Survival of G. lamblia Cysts in Turbid and in Clear
Water.  [A rather striking bar chart comparing chemical treatments under
varying conditions.  The chlorine comp ounds were basically ineffective,
with no significant effect at 30 minutes; at 8 hours the Sierra was still
totally ineffective, the bleach killed about half the cysts, and the
Halazone killed 70- 90% of the cysts (better in clear water).  The iodine
comp ounds were poor at 30 minutes in turbid water (half killed), only a
little better at 30 minutes in clear water (70-90% killed, with Potable
Aqua the best), but completely effective (100% killed) after 8 hours.]

Figure 3 - Inactivation of Giardia Cysts as a Function of Temperature
(10-minute exposures) as Indicated by Ethidium Bromide Staining and by in
vitro Excystation.  [A line chart showing cyst survival at different
temperatures.  Four combinations of Giardi a species, source, and
laboratory technique are shown, but all show approximately the same
results.  40C kills no cysts; 50C kills a lot of cysts, 60C kills most
cysts, 70C kills all cysts.]



References to commercial products shall not be construed to represent or
imply the approval or endorsement by project investigators or sponsors. 

Grant support was provided in part by the REI Environment Committee which
assumes no responsibility for the content of research reported in this



(1) Craun GF: Waterborne outbreaks of giardiasis: current status.  In:
Erlandsen SL, Meyer EA (eds): Giardia and Giardiasis.  New York: Plenum
Press, 1984; 243- 262. 

(2) Kahn FH, Visscher BR: Water disinfection in the wilderness.  West J
Med 1975; 122:450-453. 

(3) Barbour AG, Nichols CR, Fukushima T: An outbreak of giardiasis in a
group of campers.  Am J Trop Med Hyg 1980; 25:384-389. 

(4) Ongerth JE, Butler R, Donner RG, Myrick R, Merry K: Giardia cyst
concentrations in river water.  In: Advances in Water Treatment and
Analysis, Vol 15.  Denver: Am Water Works Assoc, 1988; 243-261. 

(5) Jarroll EL, Bingham AK, Meyer EA: Giardia cyst destruction:
effectiveness of six small quantity water disinfection methods.  Am J Trop
Med Hyg 1980; 29:8-11. 

(6) Schmidt SD, Meier PG: Evaluation of Giardia cyst removal via portable
water filtration devices.  J Freshwater Ecol 1984; 2:435-439. 

(7) Schaefer FW III, Rice EW, Hoff JC: Factors promoting in vitro
excystation of Giardia muris cysts.  Trans R Soc Trop Med Hyg 1984;

(8) Schupp DG, Erlandsen SL: A new method to determine Giardia cyst
viability: correlation of fluorescein diacetate and propidium iodide
staining with animal infectivity.  Appl Environ Microbiol 1987;

(9) Ongerth JE, Stibbs HH: Identification of Cryptosporidium oocysts in
river water.  Appl Environ Microbiol 1987; 53:672-676,

(10) American Public Health Assoc: Chapter 408E In: Standard Methods for
the Examination of Water and Wastewater, 15th ed.  Washington, DC: Am
Public Health Assoc, 1980; 309-310. 


Appendix A: Water Filter characteristics Listed by Manufacturers on
Packaging or Instruction Insert

[Manufacturer column omitted.  See text for this information.]

Name Filter Type Operating Operating Useful Restrictions Mode Rate Life

First Need 0.4 um microscreen hand pump 1 pt/min up to 800 A plus absorber pints

{H2OK 6 um mesh, 3 in.  gravity 1 qt/min 2000 gal A, B activated carbon

Katadyn 0.2 um ceramic, hand pump 1 qt/min many years A Pocket
Ag-impregnated Filter

Pocket 10 um (nominal), halo- mouth - - A Purifier genated resin (38% I),
suction Ag-impregnated carbon

Water Pur- Polystyrene resin bed gravity - 100 gal A, C ifier (a)  (46% I2
as I5) 

A - Does not desalinate; not for saltwater or brackish water. B - Pretreat
with I2 for bacterially contaminated water. C - Not for use with muddy
water. (a) Not described as a filter by package information. 


Appendix B: Characteristics of Disinfectant Preparations

[Manufacturer column omitted.  See text for this information.]

Name Active Chemical Recommended Application Total Halogen pH Concentration (b)  (a), (mg/liter) 

Polar Pure Crystalline iodine, 1-7 capfuls per quart 2.4 (1 6.1 99.5%
depending on temperature cap/quart) 

CEGDWT Tetraglycine hydro- 1 tablet per liter or 4.5 (1 5.6 periodate
16.7% (6.68% quart tab/quart)  titrable iodine) 

Potable Tetraglycine hydro- 1 tablet per liter or 5.3 (1 5.6 Aqua
periodate 16.7% (6.68% quart tab/quart)  titrable iodine) 

2% Iodine Iodine 0.4 ml per liter 4.5 6.5

Sierra Calcium hypochlorite & 100 crystals (50 mg)  11.6 6.7 hydrogen
peroxide Ca(OCl)2 + 6 drops H2O2 per gallon

Halazone p-dichloro-sulfamoyl 5 tablets per quart 7.5 6.7 benzoic acid, 2.87%

Chlorine sodium hypo-chlorite, 5 ml per gallon 3.9 7.1 bleach 5.25%

(a) As prepared according to package instructions. (b) In water treated
according to package instructions. 


Appendix C: Characteristics of Disinfectant Test Water

Source pH Turbidity (NTU)  Chlorine Demand (a)  (mg.liter) 

Spring-fed 6.8 0.09 0.3

Lake Washington 7.1 0.75 - 0.80 0.7

(a) 30 minutes, free chlorine demand (5). 


The authors

Address reprint requests to Jerry E. Ongerth, PhD, PE,
Assistant professor, Department of Environmental Health, SB-75,
University of Washington, School of Public Health and Community Medicine,
Seattle, WA 98195.
Dr. Stibbs is with the Department of Patho biology, also at the
School, and Mr. Macdonald is with the Department of Medical Education,
School of Medicine, both at the University of Washington; Mr. Johnson is
with the Department of Biological Chemistry, Johns Hopkins School of
Medicine, Baltimore; Dr. Frost is with the Office of Environmental
Programs, Department of Social and Health Sciences, Olympia, WA.  This
paper, submitted to the Journal January 12, 1289, was revised and accepted
for publication June 22, 1989. 



AB Prevalence and infection patterns of Cryptosporidium and Giardia
infections in horses were studied by a direct immunofluorescence staining
method. Faecal examinations of 222 horses of different age groups revealed
Cryptosporidium infection rates of 15- 31% in 66 foals surveyed in central
Ohio, southern Ohio and central Kentucky, USA. Only 1 of 39 weanlings, 0
of 46 yearlings, and 0 of 71 mares were positive. Giardia infection was
found in all age groups, although the infection rates for foals were highe
r (17-35%). Chronological study of infection in 35 foals showed that foals
started to excrete Cryptosporidium oocysts between 4 and 19 weeks and
Giardia cysts between 2 and 22 weeks of age. The cumulative infection
rates of Cryptosporidium and Giardia in foals were each 71%. Some foals
were concurrently infected with both parasites and excretion of oocysts or
cysts was intermittent and long-lasting. The longest duration of excretion
was 14 weeks for Cryptosporidium and 16 weeks for Giardia. Excretion of C
ryptosporidium oocysts stopped before weaning, while excretion of Giardia
cysts continued thereafter. Infected foals were considered the major
source of Cryptosporidium infection in foals, whereas infected mares were
deemed the major source of Giardia inf ection in foals. The high infection
rate of Giardia in nursing mares suggested a periparturient relaxation of
immunity. The results indicated that Cryptosporidium and Giardia
infections are common in horses. 


=============== Pointer to CDC Web page on Giardia:

=============== Pointer to FDA Web page on Giardia:



REI Water Filter Chart (also available at 

[Sources: REI Product Information Guide on Water Filters, Fall 1997
                plus Campmor, SweetWater, and MSR Web pages ]

                         pore  field  carbon weight pump  L/min  pumps  filter
                  cost   size  clean?        (oz)  force  flow   per L  life
                       (micron)                    (lbs)  rate          (gal)
Pur Pioneer       $ 30    .5    no    no       8.4    2    1.0    59     20
SwtWtr Walkabout  $ 35    .2    yes   yes      8.5    ?     .7     ?    100
Pur Hiker         $ 55    .3    rinse yes     11.0    8    1.5    48    200
SwtWtr Guardian   $ 60    .2    yes   yes     11.0    2    1.0    60    200
MSR Miniworks     $ 65    .3    yes   yes     14.3    8.5   .6   100   1000
1st Need Deluxe   $ 70    .1    no    lots    15.0    6    1.7    45    100
Pur Voyageur      $ 70  .3 + I  rinse yes     11.5   12    1.3    53    200
Pur Scout         $ 80  .3 + I  rinse option  12.0   11    1.0    60    200
SwtWtr Guardian+  $ 80  .2 + I  yes   yes     15.0    3     .9    60    200,90
MSR Waterworks 2  $125    .2    yes   yes     16.6   12     .8    76   1000
Pur Explorer      $130  .3 + I  self  option  24.8    5    1.4    43    400
Katadyn Mini      $139    .2    yes   no       8.2   13     .5   120   1000
Katadyn Combi     $185  .2 + I  yes   yes     29.2    ?    1.2    50  14000,60
Katadyn PF        $295    .2    yes   no      22.7   20     .7    82  15000

        Notes: cost reflects lower of Campmor or REI retail price
        pore size must be < .3 micron to filter out small bacteria
        activated carbon can reduce toxic chemicals and heavy metals
        pumping force can increase considerably as filter clogs
        output rate can decrease substantially as filter clogs
        capacity as rated by manufacturer, might not be accurate
        with silty water First Need clogs more rapidly than Pur Hiker
        models labeled "+I" use iodine to neutralize viruses and bacteria
        MSR filters do not include cost of handy stainless steel screen
        Katadyn Mini requires frequent cleaning because of small size
        under filter life, numbers after comma indicate iodine longevity
        only Explorer is self cleaning-- others require disassembly


For room reasons I left off two filters. Its specs are in order: Basic
Designs 1.0 absolute, 12 oz., 2, Granular active carbin & ceramic, $.07,
1000, 60 MINUTES!, $40.00, $60.00. Timber Line: 2.0 absolute, 6 oz., 1,
Spun Polypro, $.30, 100, 70 Seconds, $?  ?.??, $30.00. 

The filtering times are probably based on a new unit. Some units are easy
to clean, one can't be properly, and one can be cleaned on the fly. 

Lower prices can be found elsewhere than REI. REI charges list mostly. 

Notes: 1st Need, Timberline, and Basic Designs require iodine to treat
bacteria and viruses.  Katadyn and MSR require iodine to treat viruses.
Only PUR requires no additional iodine.  With carbon elements, only MSR,
1st Need, and Basic Designs remove harm ful chemicals. 


From: (Alan Malkiel) Subject: Review-Katadyn Mini

Equipment Review - Katadyn Minifilter

Specifications:  weight 8.2 oz., filters to 0.2 microns, pump force 13
lbs., output 0.5 liters per minute, cost $150. Specifications taken w/o
permission from REI catalog. 

Personal observations:  My wife and I used the Katadyn Minifilter on a 4
day backpack trip to Colorado.  Most of the trip was just below tree line. 
It did not rain during this period.  As the primary pumper, let me say I
possess reasonable upper body str ength. (Prior to the trip I built a wood
fence using hand tools and a hand post hole digger.) 

The first time I used the filter I tossed the intake screen into a fast
moving, clear trout stream.  The intake settled onto what I thought was a
clean rock, and I began pumping.  After dozens of strokes without pumping
a drop I speculated that the filter
 was defective.  After disassembly and inspection I concluded the metal
intake screen had clogged and the ceramic element had a thick "gunk"
coating.  My "clean" rock was covered with a thin layer of brown algae
which plugged the system on the first strok e. 

Disassembly was quick, requiring a half turn of the outlet spout.  The
cleaning tool is actually a metal file which scrapes off a layer of
ceramic, exposing a fresh surface.  The instructions claim 100 cleanings
are possible.  A measuring device (included ) determines when the
remaining ceramic material is worn away. The plugged metal screen was
cleaned with a finger nail.  Reassembly was equally quick but no effort
was made to keep unfiltered water from contaminating the "clean area". 

For the next attempt, I filled a 2 quart pot and dropped in the intake
hose. Contaminated water from the first dozen strokes was discarded. 
Pumping one quart required an average of 150 strokes.  Relative effort was
high, requiring a "death grip" on the f ilter body to aim the stream of
filtered water into the canteen.  Average time to filter a quart was 5
minutes.  Averages were computed over the 4 day period, during which time
3 additional cleanings were necessary while filtering 6 to 8 quarts per

Other observations:  The intake screen jumped 2 inches on each stroke and
tended to "walk" out of the pot.  A clothes pin would have been handy
here.  Of greater concern was the single drop of unfiltered water leaking
from around the pump shaft after ever y 10 to 20 strokes.  Holding the
pump at the wrong angle would allow this water to drip into the canteen. 
As a precaution I added Polar Pure iodine at half strength and doubled the
waiting period.  Finally comment - it took my wife about 10 minutes to pu
mp a quart, including rest periods. 

Conclusion.  The Katadyn Minifilter is acceptable only if:  A - Filtration
is the preferred method of water treatment. B - Weight and small size is
critical. C - Intended use is by one or two people, max. 

Cleaning is necessary after pumping 6 quarts of water with no visible
particulates (except for 10 inch trout), bringing the estimated cost to
$0.25 per quart.  Compare this to less than a penny per quart for Polar
Pure.  Pumping effort will work up a swea t and preventing unfiltered
water from contaminating filtered water is problematic.  The unit is
mechanically rugged and will probably survive greater abuse than - for
example - the First Need.  Access to critical parts is very good. 

Reviewer - Alan Malkiel


*A warning about iodine toxicity* (some individuals appear to be
susceptible to this, while many are not). 

%J Animal Health Newsletter
%I University College of Veterinary Medicine
%D July 1995
%K Canine Giardia,

According to "Understanding Nutrition" by Whitney, Hamiltion and Rolfes (a
nutrition text book), iodine is "a component of the thyroid hormone
thyroxin which helps to regulate growth, development, and metabolic rate." 
"Excessive intakes of iodine can als o cause an enlargement of the thyroid
gland... [and] depressed thyroid activity.  this goiterlike condition can
be so severe as to block the airways in infants and cause suffocation..." 
Average consumption in [the U.S.] rose from 150 micrograms per day i n
1960 .. to an all-time high of over 800 micrograms per day in 1974.  It
has since decline to about 200 to 500..."  "The toxic level at which
detectable harm results is thought to be over 2,000 micrograms per day for
an adult..."  Now to the tablets..  .  My bottle of "Potable Aqua" (which
I carry as a back-up for the broken filter) has a net contents of 0.21
ounces for 50 tablets.  Here are the calculations:  0.21 oz/50 tablets ==>
0.0042 oz/tablet = 0.1191 gram/tablet; each tablet is 6.68% Iodi ne, thus
0.0668 * 0.1191 * 1,000,000 = 7,956 micrograms of iodine per tablet.  Note
that this is PER TABLET. One tablet treats a quart of water.  For Giardia
control, or if the water is cold or of poor quality, the directions say to
use 2 tablets per qu art.  (Who doesn't want to control giardia ?!!)  The
average backpacker should be drinking a gallon a day (varies widely).  One
gallon treated with iodine at the rate of 1 tablet per quart would contain
about 31,800 micrograms of iodine.  At the rate of 2 tablets per quart, it
would be 63,600 micrograms.  These levels exceed the *believed* toxicity
level by a mile.  This is the reason that prolonged use of iodine isn't
recommended, and the reason (in addition to taste/smell) that *I* switched
to a fi lter.  As for short term use I guess the relevant question is,
"How's your thyroid feeling?"

Medicine for Mountaineering, 3rd edition:
"Ingested iodine is absorbed as iodide, and an average adult requires 150 
to 200 micrograms per day.  Daily consumption of one to two liters of 
water disinfected with 8 mg/L of iodine would provide 30 to 80 times that 
amount, but such quantities would not affect most individuals with normal 
thyroid function.  Almost all patients who have developed iodide goiter 
after consuming excess iodide have consumed far larger amounts for six 
months to more than 5 years."

> A) What is the effect, if any, of standard, household dish detergent
> on Giardia?

No effect.

> B) What is the effect, if any, on Giardia which has been subjected to
> the temperatures of a standard hot water heater for several hours?

The FAQ said "Giardia is killed in less than a minute at 176 F (80 C)"
and most household hot water heaters are not cranked above 140 F.

This is a stupid question.  People should not drink hot water-heated
water because it often contains high concentrations of lead and/or PVC
leached from pipes.

The hot water heater question is interesting in one sense, 
i.e. if you had no other choice and were principally worried about 
infectious agents, hot tap water would be better than cold.  However, 
that situation is pretty contrived, and it doesn't seem like there are 
any data to support a recommendation specific to Giardia.

> C) How long does Giardia survive on dry plates and utensils which were
> rinsed in water that might contain Giardia?

Weeks?  Months?  Years?  I don't know-- cysts are quite durable.
The answer to the third question is very important-- unfortunately
I don't know.  Can't Giardia cysts survive on dry plates for months?

The final 
one is, as far as I know, an open question.  In sunlight, it would 
probably be killed in under an hour on a clean, dry surface.  On a 
plate stuffed into a backpack?  Who knows?  The cysts can survive for 
years in soil, but that's a different situation.

Bill's answers are as complete as any I could provide.  Giardia can be 
killed by household bleach, but not at concentrations you would want 
to drink.

Date: Fri, 20 Mar 1998 10:09:03 -0800 (PST)
From: Bill Tuthill <>
Message-Id: <>
To:, eugene
Subject: Re:  Summary of revamps

Eugene, I've made it easy for you.

A) What is the effect of ordinary dish detergent on Giardia?

It has no effect.  To kill Giardia cysts, you must rinse dishes in an
iodine solution, or in hot water above 80 C (176 F).

B) What is the effect, if any, on Giardia subjected to the temperatures
   of a standard hot water heater for several hours?

Most household water heaters cannnot heat water above 60 C (140 F),
which is not hot enough to kill Giardia.  To kill bacteria and viruses,
water must be even hotter.  Moreover, it is a bad idea to drink hot
tap water because it often contains high concentrations of lead and/or
PVC leached from pipes.

C) How long does Giardia survive on dry plates and utensils rinsed in
   water that might contain Giardia?

This is an open question.  In sunlight, Giardia cysts are probably
killed in under an hour on a clean, dry surface.  On a plate stuffed
into a backpack, who knows?  Cysts can survive for years in soil, but
that's a different situation.

[1] Meyer, EA (ed), Giaridasis (1990), Human Parasitic Diseases, Volume 3,
Elsevier, Amsterdam
[2] Erlandsen, SL, and Meyer, EA (1984), Giardia and Giardiasis,
Plenum Press, NY
[3] Frame, JD (1984), Amebiasis and Giardiasis. In: Ellner, PD (ed),
Infectious Diarrheal Diseases, pp. 117-140, Marcel Dekker, NY

Prevalence of Giardia spp. and Cryptosporidium spp. on dairy farms in
southeastern New York state.
Prev Vet Med. 2003 May 30;59(1-2):1-11.

Risk of giardiasis in Aucklanders: a case-control study.
Int J Infect Dis. 2002 Sep;6(3):191.

A comparative study of the intestinal parasites prevalent among
children living in rural and urban settings in and around Chennai.
J Commun Dis. 2002 Mar;34(1):35-9.

Pathogen survival in swine manure environments and transmission of
human enteric illness--a review.
J Environ Qual. 2003 Mar-Apr;32(2):383-92.

Factors associated with the likelihood of Giardia spp. and
Cryptosporidium spp. in soil from dairy farms.
J Dairy Sci. 2003 Mar;86(3):784-91.

Faecal contamination of greywater and associated microbial risks.
Water Res. 2003 Feb;37(3):645-55.

Microbial agents associated with waterborne diseases.
Crit Rev Microbiol. 2002;28(4):371-409. Review.

Giardia in beaver (Castor canadensis) and nutria (Myocastor coypus)
from east Texas.
J Parasitol. 2002 Dec;88(6):1254-8.

ARSENIC references

Chwirka, J. D. Removing Arsenic from groundwater
Journal of the American Water Works Association
v92, no3, pp. 79-88

Focazio M. J. A retrospective analysis of the occurrence of arsenic in
ground water resources. USGS Water resources investigation report 99-4279.,0,4844133.story


Diseases Branch Division of Parasitic Diseases Centers for Disease Control

Transmission and Control


During the past fifteen years giardiasis has been recognized as one of the
most frequently occurring waterborne diseases in the United States (1).
Giardia lamblia have been discovered in the United States in places as far
apart as Estes Park, Colorado (ne ar the Continental Divide); Missoula,
Montana; Wilkes-Barre, Scranton, and Hazleton, Pennsylvania; and
Pittsfield and Lawrence, Massachusetts just to name a few. In light of
recent large outbreaks of waterborne giardiasis, it seem timely to present
reliab le information on the way in which giardiasis is acquired, treated,
and prevented. 

Giardiasis: Prevalence and Symptoms

Giardiasis is a disease caused by a one-celled parasite with the
scientific name Giardia lamblia. The disease is characterized by
intestinal symptoms that usually last one week or more and may be
accompanied by one or more of the following: diarrhea, abdo minal cramps,
bloating, flatulence, fatigue, and weight loss (see Table 1). Although
vomiting and fever are listed in Table 1 as relatively frequent symptoms,
they have been uncommonly reported by people involved in waterborne
outbreaks of giardiasis in t he United States. Table 1 also suggests that
13 percent of patients with giardiasis may have blood in their stool.
Giardia, however, rarely causes intestinal bleeding. Therefore, blood in
the stool of a patient with giardiasis almost always indicates the
presence of a second disease. 

While most Giardia infections persist only for one or two months, some
people undergo a more chronic phase, which can follow the acute phase or
may become manifest without an antecedent acute illness. The chronic phase
is characterized by loose stools, an d increased abdominal gassiness with
cramping, flatulence and burping. Fever is not common, but malaise,
fatigue, and depression may ensue (2). For a small number of people, the
persistence of infection is associated with the development of marked
malabso rption and weight loss (3). Similarly, lactose (milk) intolerance
can be a problem for some people. This can develop coincidentally with the
infection or be aggravated by it, causing an increase in intestinal
symptoms after ingestion of milk products. 

Some people may have several of these symptoms without evidence of
diarrhea or have only sporadic episodes of diarrhea every 3 or 4 days.
Still others may not have any symptoms at all. Therefore, the problem may
not be whether you are infected with the pa rasite or not, but how
harmoniously you both can live together, or how to get rid of the parasite
(either spontaneously or by treatment) when the harmony does not exist or
is lost. 

Medical Treatment

Three drugs are available in the United States to treat giardiasis:
	quinacrine (Atabrine*),
	metronidazole (Flagyl*), and
	furazolidone (Furoxone*).
All are prescription drugs. In a recent review of drug trials
in which the efficacies of these drugs were co mpared, quinacrine produced
a cure in 93% of 129 patients, metronidazole cured 92% of 219, and
furazolidone cured 84% of 150 patients (4). Quinacrine is generally the
least expensive of the anti-Giardia medications but it often causes
vomiting in children younger than 5 years old.
Although the treatment of giardiasis is not an
FDA-approved indication for metronidazole, the drug is commonly used for
this purpose. Furazolidone is the least effective of the three drugs, but
is the only anti-Giardia medicatio n that comes as a liquid preparation,
which makes it easier to deliver the exact dose to small children and
makes it the most convenient dosage form for children who have difficulty
taking pills. Cases of chronic giardiasis refractory to repeated courses
of therapy have been noted, one of which responded to combined quinacrine
and metronidazole treatment (5). 

(*) Use of trade names is for purposes of identification only. 

Etiology and Epidemiology

Giardiasis occurs worldwide. In the United States, Giardia is the parasite
most commonly identified in stool specimens submitted to state
laboratories for parasitologic examination. From 1977 through 1979,
approximately 4% of 1 million stool specimens sub mitted to state
laboratories were positive for Giardia (6). Other surveys have
demonstrated Giardia prevalence rates ranging from 1 to 20% depending on
the location and ages of persons studied. Giardiasis ranks among the top
20 infectious diseases that ca use the greatest morbidity in Africa, Asia,
and Latin America (7); it has been estimated that about 2 million
infections occur per year in these regions (8). 

People who are at highest risk for acquiring a Giardia infection in the
United States may be placed into five major categories: 

1) People in cities whose drinking water originates from streams or rivers
and whose water treatment process does not include filtration, or
filtration is ineffective because of malfunctioning equipment.
2) Hikers/campers/outdoorspeople.
3) International travelers
4) Children who attend day-care centers, day-care center staff,
and parents and siblings of children infected in day-care centers.
5) Homosexual men. 

People in categories 1, 2, and 3 have in common the same general source of
infections, i.e., they acquire Giardia from fecally contaminated drinking
water. The city resident usually becomes infected because the municipal
water treatment process does not i nclude a filter that is necessary to
physically remove the parasite from the water. The number of people in the
United States at risk (i.e., the number who receive municipal drinking
water from unfiltered surface water) is estimated to be 20 million. Inte
rnational travelers may also acquire the parasite from improperly treated
municipal waters in cities or villages in other parts of the world,
particularly in developing countries. In Eurasia, only travelers to
Leningrad appear to be at increased risk. In prospective studies, 88% of
U.S. and 35% of Finnish travelers to Leningrad who had negative stool
tests for Giardia on departure to the Soviet Union developed symptoms of
giardiasis and had positive tests for Giardia after they returned home
(10,11). With the exception of visitors to Leningrad, however,
Giardia has not been implicated as a major cause of traveler's diarrhea.
The parasite has been detected in fewer than 2% of travelers who
develop diarrhea. Hikers and campers risk infection every time
they drink untreated raw water from a stream or river. 

Persons in categories 4 and 5 become exposed through more direct contact
with feces of an infected person, e.g., exposure to soiled diapers of an
infected child (day-care center-associated cases), or through direct or
indirect anal-oral sexual practices i n the case of homosexual men. 

Although community waterborne outbreaks of giardiasis have received the
greatest publicity in the United States during the past decade, about half
of the Giardia cases discussed with staff of the Centers for Disease
Control in the past 2 to 3 years have a
 day-care center exposure as the most likely source of infection. Numerous
outbreaks of Giardia in day-care centers have been reported in recent
years. Infection rates for children in day-care center outbreaks range
from 21 to 44% in the United states and
 from 8 to 27% in Canada (12,13,14,15,16,17). The highest infection rates
are usually observed in children who wear diapers (l to 3 years of age).
In one study of 18 randomly selected day care centers in Atlanta (CDC
unpublished data), 10% of diapered chi ldren were found infected.
Transmission from this age group to older children, day-care staff, and
household contacts is also common. About 20% of parents caring for an
infected child will come infected. 

It is important that local health officials and managers of water utility
companies realize that sources of Giardia infection other than municipal
drinking water exist. Armed with this knowledge, they are less likely to
make a quick (and sometimes wrong) assumption that a cluster of recently
diagnosed cases in a city is related to municipal drinking water. Of
course, drinking water must not be ruled out as a source of infection when
a larger than expected number of cases are recognized in a community, but
 the possibility that the cases are associated with a day-care center
outbreak, drinking untreated stream water, or international travel should
also be entertained. 

Parasite Biology

To understand the finer aspects of Giardia transmission and the strategies
for control, one must become familiar with several aspects of the
parasite's biology. Two forms of the parasite exist: a trophozoite and a
cyst, both of which are much larger than bacteria (see Figure 1).
Trophozoites live in the upper small intestine where they attach to the
intestinal wall by means of a disc-shaped suction pad on their ventral
surface. Trophozoites actively feed and reproduce at this location. At
some time during
 the trophozoite's life, it releases its hold on the bowel wall and floats
in the fecal stream through the intestine. As it makes this journey, it
undergoes a morphologic transformation into an egglike structure called a
cyst. The cyst, which is about 6 t o 9 micrometers in diameter x 8 to 12
micrometers (1/100 millimeter) in length, has a thick exterior wall that
protects the parasite against the harsh elements that it will encounter
outside the body. This cyst form of the parasite is infectious for other
 people or animals. Most people become infected either directly by
hand-to-mouth transfer of cysts from the feces of an infected individual,
or indirectly by drinking feces-contaminated water. Less common modes of
transmission included ingestion of fecall y contaminated food and
hand-to-mouth transfer of cysts after touching a fecally contaminated
surface. After the cyst is swallowed, the trophozoite is liberated through
the action of stomach acid and digestive enzymes and becomes established
in the small intestine. 

Although infection after the ingestion of only one Giardia cyst is
theoretically possible, the minimum number of cysts shown to infect a
human under experimental conditions is ten (18). Trophozoites divide by
binary fission about every 12 hours. What this
 means in practical terms that if a person swallowed only a single cyst,
reproduction at this rate would result in more than 1 million parasites 10
days later, and 1 billion parasites by day 15. 

The exact mechanism by which Giardia causes illness is not yet well
understood, but is not necessarily related to the number of organisms
present. Nearly all of the symptoms, however, are related to dysfunction
of the gastrointestinal tract. The parasite rarely invades other parts of
the body, such as the gall bladder or pancreatic ducts. Intestinal
infection does not result in permanent damage. 


Data reported to the CDC indicate that Giardia is the most frequently
identified cause of diarrheal outbreaks associated with drinking water in
the United States. The remainder of this article will be devoted to
waterborne transmission of Giardia. Waterbo rne epidemics of giardiasis
are a relatively frequent occurrence. In 1983, for example, Giardia was
identified as the cause of diarrhea in 68% of waterborne outbreaks in
which the causal agent was identified (19). From 1965 to 1982, more than
50 waterborn e outbreaks were reported (20). In 1984, about 250,000 people
in Pennsylvania were advised to boil drinking water for 6 months because
of Giardia-contaminated water. Many of the municipal waterborne outbreaks
of Giardia have been subjected to intense stud y to determine their cause.
Several general conclusions can be made from data obtained in those
studies. Waterborne transmission of Giardia in the United States usually
occurs in mountainous regions where community drinking water is obtained
from clear ru nning streams, is chlorinated but is not filtered before
distribution. Although mountain streams appear to be clean, fecal
contamination upstream by human residents or visitors, as well as by
Giardia-infected animals such as beavers, has been well documen ted. It is
worth emphasizing that water obtained from deep wells is an unlikely
source of Giardia because of the natural filtration of water as it
percolates through the soil to reach underground cisterns. Well-water
sources that pose the greatest risk of
 fecal contamination are those that are poorly constructed or improperly
located. A few outbreaks have occurred in towns that included filtration
in the water treatment process, but the filtration was not effective in
removing Giardia cysts because of def ects in filter construction, poor
maintenance of the filter media, or inadequate pretreatment of the water
before it was filtered. Occasional outbreaks have also occurred because of
accidental cross-connections between water and sewerage systems. 

One can conclude from these data that two major ingredients are necessary
for waterborne outbreak. First, there must be Giardia cysts in untreated
source water and, second, the water purification process must either fail
to kill or fail to remove Giardia cysts from the water. 

Although beavers are often blamed for contaminating water with Giardia
cysts, it seems unlikely that they are responsible for introducing the
parasite into new areas. It is far more likely that they are also victims:
Giardia cysts may be carried in untrea ted human sewage discharged into
the water by small-town sewage disposal plants or originate from cabin
toilets that drain directly into streams and rivers. Backpackers, campers,
and sports enthusiasts may also deposit Giardia-contaminated feces in the
en vironment that are subsequently washed into streams by rain. In support
of this concept is a growing amount of data that indicate a higher Giardia
infection rate in beavers living downstream from U.S. National Forest
campgrounds compared with a near zero rate of infection in beavers living
in more remote areas. 

Although beavers may be unwitting victims in the Giardia story, they still
play an important part in the transmission scheme, because they can (and
probably do) serve as amplifying hosts. An amplifying host is one that is
easy to infect, serves as a good habitat for the parasite to reproduce,
and, in the case of Giardia, returns millions of cysts to the water for
every one ingested. Beavers are especially important in this regard
because they tend to defecate in or very near the water, which ensures
that most of the Giardia cysts excreted are returned to the water

The contribution of other animals to waterborne outbreaks of Giardia is
less clear. Muskrats (another semiaquatic animal) have been found in
several parts of the United States to have high infection rates (30 to
40%) (2l). Recent studies have shown that m uskrats can be infected with
Giardia cysts obtained from humans and beavers. Occasional Giardia
infections have been reported in coyotes, deer, elk, cattle, dogs, and
cats, but not in horses and sheep, encountered in mountainous regions of
the United Stat es. Naturally occurring Giardia infections have not been
found in most other wild animals (bear, nutria, rabbit, squirrel, badger,
marmot, skunk, ferret, porcupine, mink, raccoon, river otter, bobcat,
lynx, moose, bighorn sheep) (22). 

Removal from Municipal Water Supplies

During the past 10 years, scientific knowledge about what is required to
kill or remove Giardia cysts from a contaminated water supply has
increased considerably. For example, it is known that cysts can survive in
cold water (4 deg C) for at least 2 month s and that they are killed
instantaneously by boiling water (100 deg C) (23,24). It is not known how
long the cysts will remain viable at other water temperatures (e.g., at 0
deg C or in a canteen at 15-20 deg C), nor is it known how long the
parasite wil l survive on various environment surfaces, e.g., under a pine
tree, in the sun, on a diaper-changing table, or
in carpets in a day-care center.

The effect of chemical disinfection, such as chlorine, on the viability of
Giardia cysts is an even more complex issue. It is clear from the number
of waterborne outbreaks of Giardia that have occurred in communities where
chlorine was employed as a disin fectant that the amount of chlorine used
routinely for municipal water treatment is not effective against Giardia
cysts. These observations have been confirmed in the laboratory under
experimental conditions (25,26,27). This does not mean, however, that c
hlorine does not work at all. It does work under certain favorable
conditions. Without getting too technical, one can gain some appreciation
of the problem by understanding a few of the variables that influence the
efficacy of chlorine as a disinfectant. 

1) Water pH: at pH values above 7.5, the disinfectant capability of
chlorine is greatly reduced.  2) Water temperature: the warmer the water,
the higher the efficacy.  Thus, chlorine does not work well in ice-cold
water from mountain streams. 3) O rganic content of the water: mud,
decayed vegetation, or other suspended organic debris in water chemically
combines with chlorine making it unavailable as a disinfectant. 4)
Chlorine contact time: the longer Giardia cysts are exposed to chlorine ,
the more likely it is that the chemical will kill them. 5) Chlorine
concentration: the higher the chlorine concentration, the more likely
chlorine will kill Giardia cysts. Most water treatment facilities try to
add enough chlorine to give a free ( unbound)  chlorine residual at the
customer tap of 0.5 mg per liter of water.

The five variables above are so closely interrelated that an unfavorable
occurrence in one can often be compensated for by improving another. For
example, if chlorine efficacy is expected to be low because water is
obtained from an icy stream, either the chlorine contact time or chlorine
concentration, or both could be increased. In the case of
Giardia-contaminated water, it might be possible to produce safe drinking
water with a chlorine concentration of 1 mg per liter and a contact time
as short as 10 m inutes if all the other variables were optimal (i.e., pH
of 7.0, water temperature of 25 deg C, and a total organic content of the
water close to zero). On the other hand, if all of these variables were
unfavorable (i.e., pH of 7.9, water temperature of 5
 deg C, and high organic content), chlorine concentrations in excess of 8
mg per liter with several hours of contact time may not be consistently
effective. Because water conditions and water treatment plant operations
(especially those related to water r etention time and, therefore, to
chlorine contact time) vary considerably in different parts of the United
States, neither the U.S. Environmental Protection Agency nor the CDC has
been able to identify a chlorine concentration that would be safe yet
effec tive against Giardia cysts under all water conditions. Therefore,
the use of chlorine as a preventive measure against waterborne giardiasis
generally has been used under outbreak conditions when the amount of
chlorine and contact time have been tailored t o fit specific water
conditions and the existing operational design of the water utility. 

In an outbreak, for example, the local health department and water utility
may issue an advisory to boil water, may increase the chlorine residual at
the consumer's tap from 0.5 mg per liter to 1 or 2 mg per liter, and, if
the physical layout and operatio n of the water treatment facility permit,
increase the chlorine contact time. These are emergency procedures
intended to reduce the risk of transmission until a filtration device can
be installed or repaired or until an alternative source of safe water, s
uch as a well, can be made operational. 

The long-term solution to the problem of municipal waterborne outbreaks of
giardiasis will involve improvements in and more widespread use of filters
in the municipal water treatment process. The sand filters most commonly
used in municipal water treatmen t today cost millions of dollars to
install, which makes them unattractive for many small communities.
Moreover, the pore sizes in these filters are not sufficiently small to
remove a Giardia (6 to 9 micrometers x 8 to 12 micrometers).
For the sand filter to remove Giardia cysts from the water effectively,
the water must receive some additional treatment before it reaches the filter.
In addition, the flow of water through the filter bed must
be carefully regulated. 

An ideal prefilter treatment for muddy water would include sedimentation
(a holding pond where the large suspended particles are allowed to settle
out by the action of gravity) followed by flocculation or coagulation (the
addition of chemicals such as alu m or ammonium to cause microscopic
particles to clump together). The large particles resulting from the
flocculation/coagulation process, including Giardia cysts bound to other
microparticulates, are easily removed by the sand filter. Chlorine is then
add ed to kill the bacteria and viruses that may escape the filtration
process. If the water comes from a relatively clear source, chlorine may
be added to the water before it reaches the filter. The point here is that
successful operation of a complete water treatment facility is
a complex process that requires considerable training.
Troubleshooting breakdowns or recognizing potential problems in
the system before they occur often requires the skills of an engineer.
Unfortunately, most small water utilities that have a water treatment
facility that includes filtration cannot afford the services of a
full-time engineer. Filter operation or maintenance problems in such
systems may not be detected until a Giardia outbreak is recognized in the
community. The bot tom line is that although, in reference to municipal
systems, water filtration is the best that water treatment technology has
to offer against waterborne giardiasis, it is not infallible. For
municipal water filtration facilities to work properly, they m ust be
properly constructed, operated, and maintained. 

Water Disinfection in the Out-of-Doors

Whenever possible, persons in the out-of-doors should carry drinking water
of known purity with them. When this is not practical, and water from
streams, lakes, ponds, and other outdoor sources must be used, time should
be taken to disinfect the water bef ore drinking it. 


Boiling water is one of the simplest and most effective ways to purify
water. Boiling for 1 minute is adequate to kill Giardia as well as most
other bacterial or viral pathogens likely to be acquired from drinking
polluted water. 

Chemical Disinfection

Disinfection of water with chlorine or iodine is considered less reliable
than boiling for killing Giardia. However, it is recognized that boiling
drinking water is not practical under many circumstances. Therefore, when
one cannot boil drinking water, chemical disinfectants such as iodine or
chlorine should be used. This will provide some protection against Giardia
and will destroy most bacteria and viruses that cause illness. Iodine or
chlorine concentrations of 8 mg/liter (8ppm) with a minimum contact time
of 30 minutes are recommended. If the water is cold (less than 10 deg C or
5O deg F) we suggest a minimum contact time of 60 minutes. If you have a
choice of disinfectants, use iodine. Iodine's disinfectant activity is
less likely to be reduced by un favorable water conditions, such as
dissolved organic material in water or by water with a high pH, than chlorine. 

Below are instructions for disinfecting water using household tincture of
iodine or chlorine bleach. If water is visibly dirty, it should first be
strained through a clean cloth into a container to remove any sediment or
floating matter. Then the water sh ould be treated with chemicals as follows: 


Tincture of iodine from the medicine chest or first aid kit can be used to
treat water. Mix thoroughly by stirring or shaking water in container and
let stand for 30 minutes. 

Tincture of Iodine Drops* to be Added per Quart or Liter Clear Water Cold
or Cloudy Water**

    2% 5 10

* 1 drop = 0.05ml

** Very turbid or very cold water may require prolonged contact time; let
stand up to several hours or even overnight. 


Liquid chlorine bleach used for washing clothes usually has 4% to 6%
available chlorine. The label should be read to find the percentage of
chlorine in the solution and the treatment schedule below should be

                           Drops* to be Added per Quart or Liter Available
			Clear Water Cold or Cloudy Water**

     1% 10 20 4% to 6% 2 4 7% to lO% 1 2 Unknown 10 20

* 1 drop = 0.05ml

** Very turbid or very cold water may require prolonged contact time; let
stand up to several hours or even overnight. 

 Mix thoroughly by stirring or shaking water in container and let stand
for 30 minutes. A slight chlorine odor should be detectable in the water;
if not, repeat the dosage and let stand for an additional 15 minutes
before using. 


Newcomers in the battle against waterborne giardiasis include a variety of
portable filters for field or individual use as well as some household
filters. Manufacturers' data accompanying these filters indicate that some
can remove particles the size of a
 Giardia cyst or smaller and may be capable of providing a source of safe
drinking water for an individual or family during a waterborne outbreak.
Such devices, if carefully selected, might also be useful in preventing
giardiasis in international travelers, backpackers, campers, sportsmen,
or persons who live or work in areas where water is known to be contaminated. 

Unfortunately, there are yet few published reports in the scientific
literature detailing both the methods used and the results of tests
employed to evaluate the efficacy of these filters against Giardia. Until
more published experimental data become avai lable, there are a few common
sense things that a consumer should look for when selecting a portable or
household filter. The first thing to consider is the filter media. Filters
relying solely on ordinary or silver-impregnated carbon or charcoal should
be avoided, because they are not intended to prevent, destroy, or repel
micro-organisms. Their principal use is to remove undesirable chemicals,
odors, and very large particles such as rust or dirt. 

Some filters rely on chemicals such as iodide-impregnated resins to kill
Giardia. While properly designed and manufactured iodide-impregnated resin
filters have been shown to kill many species of bacteria and virus present
in human feces, their efficacy a gainst Giardia cysts is less
well-established. The principle under which these filters operate is
similar to that achieved by adding the chemical disinfectant iodine to
water, except that the micro-organisms in the water pass over the
iodide-impregnated d isinfectant as the water flows through the filter. 

While the disinfectant activity of iodide is not as readily affected as
chlorine by water pH or organic content, iodide disinfectant activity is
markedly reduced by cold water temperatures. Experiments on Giardia
indicate that many of the cysts in cold wa ter (4 deg C) remain viable
after passage through filters containing tri-iodide or penta-iodide
disinfectants (28). As indicated earlier, longer contact times (compared
to those required to kill bacteria) are required when using chemical
filters to proces s cold water for Giardia protection. Presently available
chemical filters also are not recommended for muddy or very turbid water.
Additionally, filters relying solely on chemical action usually give no
indication to the user when disinfectant activity ha s been depleted. 

The so-called microstrainer types of filters are true filters.
Manufacturer data accompanying these filters indicate that some have a
sufficiently small pore size to physically restrict the passage of some
micro-organisms through the filter. The types of filter media employed in
microstraining filters include orlon, ceramic, and proprietary materials.
Theoretically, a filter having an absolute pore size of less than 6
micrometers might be able to prevent Giardia cysts of 8 to 10 micrometers
in diameter fr om passing. However, when used as a water sampling device
during community outbreaks, portable filters in the 1- to 3- micrometer
range more effectively removed Giardia cysts from raw water than filters
with larger pore sizes. For effective removal of bac terial or viral
organisms which cause disease in humans, microstraining filters with pore
sizes of less than 1 micrometer are advisable. However, the smaller the
pores, the more quickly the filters will tend to clog. To obtain maximum
filter life, and as a matter of reasonable precaution, the cleanest
available water source should always be used. Keep in mind, however, that
even sparkling, clear mountain streams can be heavily contaminated. 

Secondly, because infectious organisms can be concentrated on the filter
element/media, it is important to consider whether the filter element can
be cleaned or replaced without posing a significant health hazard to the user.
Properly engineered portable filters should also minimize the
possibility of contaminating the "clean water side" of the filter with
contaminated water during replacement or cleaning of the filter element.
This is especially important for filters used in the field where they are
ofte n rinsed or "cleaned" in a stream or river that may be contaminated. 

Ongerth (29) recently evaluated four filters (First Need, H20K, Katadyn,
the Pockett Purifier) for their ability to remove Giardia cysts from water.
Only the First Need and Katadyn filters removed 100% of the cysts. 


In conclusion, during the past fifteen years, giardiasis has been
recognized as one of the most frequently occurring waterborne diseases in
the United States. The most common sources of water contamination include
improperly treated municipal sewage, infe cted animals, and indiscriminate
defecation by outdoorsmen. Chlorine concentrations in the 0.1 mg per liter
to 0.5 mg per liter range are largely ineffective against Giardia at the
contact times commonly employed by municipal water utilities. The long-term
solution to the problem of municipal waterborne outbreaks of giardiasis
will involve appropriate pretreatment combined with improvements in and
more widespread use of filters in the municipal water treatment process.
While both micrometer- and submicrom eter-rated filters are being employed
on a limited scale for personal or household use, further evaluation of
the efficacy of filters distributed by different manufacturers is needed
to enable individuals and public health personnel to distinguish those
that are safe and effective from those that are not. 

TABLE I Percentage Number of Patients


   Diarrhea* 84 516 Malaise 80 56 Weakness 72 324 Abdominal cramps 63 412
Weight loss (O.5 - 1 1 kg)  63 412 Greasy, foul smelling stools 59 412
Nausea 57 444 Headaches 53 92 Anorexia 49
        156 Abdominal bloating 45 380 Flatulence 41 388 Constipation 25 88
Vomiting 24 488 Fever
                            22 32

Physical finding

   Abdomen tender to palpitation 66 92

Laboratory findings Blood Anemia 15 124 Leukocytosis 9 32

   Stool Increased mucus 56 32 Increased neutral fats 50 32 Blood 13 156

* Index symptom; may be biased (upward) 

 TABLE 1 - Based on data from Fifty diseases: Fifty Diagnoses, by M.G.
Periroth and D.J. Weiland. Year Book Medical Publishers, Inc., Chicago,
1981, pp. 158-159. Reprinted by special arrangement with Year Book
Publishers, Inc. 


1.  Craun, Gunther T. Waterborne Giardiasis in the United States: A
review.  American Journal of Public Health 69:817-819, 1979. 

2.  Weller, Peter F. Intestinal Protozoa: Giardiasis. Scientific American
Medicine, 1985

3.  Id. 2. 

4.  Davidson, R.A. Issues in Clinical Parasitology: The treatment of
Giardiasis.  Am J. Gastroenterol. 79:256-261, 2984

5.  Id. 2. 

6.  Intestinal Parasite Surveillance, Annual Summary 1978, Atlanta,
Centers for Disease Control, 1979. 

7.  Walsh, J.D. Warren K. s. Selective Primary Health Care: An Interim
Strategy for Disease Control in developing countries. N. Engl. J. Med.,
301:967-974, 1979. 

8.  Walsh, J.A. Estimating the Burden of Illness in the Tropics, In
Tropical and Geographic Medicine, Edited by K.S. Warren and A.F. Mahmoud,
McGraw-Hill, New York, 1981, pp 1073-1085. 

9.  Weniger, B.D., Blaser, MlJ., Gedrose, J., Lippy, E.C., Juranek, D.D.
an Outbreak of Waterborne Giardiasis Associated with Heavy Water Runoff
due to Warm Weather and Volcanic Ashfall.  Am. J. Public Health
78:868-872, 1983. 

10. Brodsky, R.E., Spencer, H.C., Schultz, M.G. Giardiasis in American
Travelers to the Soviet Union. J. Infect Dis. 130:319-323, 1974.

11. Jokipii, L., Jokipii, A.M.M. Giardiasis in Travelers: A prospective
Study.  J. Infect. Dis., 130:295-299, 1974. 

12. Black, R.E., Dykes, A.C., Anderson, K.E., Wells, J.G., Sinclair, S.P.,
Gary, G.W., Hatch, M.H., Gnagarosa, E.J. Handwashing to Prevent Diarrhea
in Day-Care Centers. Am. J. Epidemiol. 113:445-451, 1981. 

13. Pickering, L.K., Woodward, W.E., DuPont, H. L., Sullivan, P.
Occurrence of Giardia lamblia in Children in Day Care Centers. J. Pediatr.
104:522-526, 1984. 

14. Sealy, D.P., Schuman, S.H. Endemic Giardiasis and Day Care. Pediatrics
72:154-158, 1983.

15. Pickering, L.K., Evans, D.G., DuPont, H.L., Vollet, J.J., III, Evans,
D.J., Jr. diarrhea Caused by Shigella, Rotavirus, and Giardia in Day-care
Centers: Prospective Study. J. Peidatr., 99:51-56, 1981. 

16. Keystone, J.S., Yang, J., Grisdale, D., Harrington, M., Pillow, L.,
Andreychuk, R. Intestinal Parasites in Metropolitan Toronto Day-Care
Centres. Can J. Assoc. J. 131:733-735, 1984. 

17. Keystone, J.S., Kraden, S., Warren, M.R. Person-to-Person Transmission
of Giardia lamblia in Day-Care Nurseries. Can. Med. Assoc. J. 119:241-242,
247-248, 1978. 

18. Rendtorff, R.C. The Experimental Transmission of Human Intestinal
Protozoan Parasites. II. Giardia lamblia cysts Given In Capsules, Am. J.
Hygiene 59:209-220, 1954. 

19. Water-related Disease Outbreaks Surveillance, Annual Summary 1983.
Atlanta, Centers for Disease Control, 1984. 

20. Craun, G.F. Waterborne Outbreaks of Giardiasis--Current Status in
Giardia and Giardiasis, edited by S.L. Erlandsen and E.A Meyer. Pleunu
Press. New York, 1984, pp 243-261. 

21. Frost, F. Plan, B., Liechty, B. Giardia Prevalence in Commercially
Trapped Mammals. J. Environ. Health 42:245-249. 

22. Id. 21. 

23. Id. 18. 

24. Bingham, A.K., Jarroll, E.L., Meyer, E.A. Radulescu, S. Introduction
of Giardia Excystation and the effect of Temperature on cyst Viability
compared by Eosin-Exclusion and In Vitro Excystation in Waterborne
Transmission of Giardiasis. Edit ed by J. Jakubowski and H. C. Hoff, U.S. 
Environmental Protection Agency, Washington, DC, 1979, pp. 217-229. 

25. Jarroll, E.L., Bingham, A.K., Meyer, E.A. Effect of Chlorine on
Giardia lamblia Cyst Viability. Appl. Environ. Microbiol. 41:483-487,

26. Jarroll, E.L., Jr., Bingham, A.K. Meyer, E.A. Inability of an
Iodination Method to Destroy completely Giardia Cysts in Cold Water. West
J. Med.  132:567-569, 1980. 

27. Jarroll, E.L., Jr., Bingham, A.K., Meyer, E.A. Giardia Cyst
Destruction:  Effectiveness of Six Small-Quantity Water Disinfection
Methods. Am. J.  Trop. Med. Hygiene 29:8-11, 1980. 

28. Marchin, B.L., Fina, L.R., Lambert, J.L., Fina, G.T. Effect of resin
disinfectants--13 and --15 on Giardia muris and giardia lamblia. Appl
Environ. Microbiol. 46:965-9, 1983. 

29. Ongerth JE, Johnson RL, Macdonald SC, Frost F, Stibbs HH. Back-country
water treatment to prevent giardiasis. Am J Public Health

Looking for an H-912 (container).

------------ And now a word from our sponsor ----------------------
For a quality mail server, try SurgeMail, easy to install,
fast, efficient and reliable.  Run a million users on a standard
PC running NT or Unix without running out of power, use the best!
----  See  ----

User Contributions:

Comment about this article, ask questions, or add new information about this topic:


Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Part8 - Part9 - Part10 - Part11 - Part12 - Part13 - Part14 - Part15 - Part16 - Part17 - Part18 - Part19 - Part20 - Part21 - Part22 - Part23 - Part24 - Part25 - Part26 - Part27 - Part28

[ Usenet FAQs | Web FAQs | Documents | RFC Index ]

Send corrections/additions to the FAQ Maintainer:,,

Last Update March 27 2014 @ 02:11 PM