Food Poisoning - Causes
Food poisoning is caused by toxins released by bacteria and other organisms. These toxins (except those from Clostridium botulinum ) cause inflammation
of the stomach and intestines. The result is abdominal (stomach) muscle cramping, vomiting, diarrhea, fever, and possibly dehydration. Dehydration is the process by which the body loses water faster than it should.
About fifty thousand cases of Salmonella poisoning were reported in the United States in 1995. The CDC estimates that between two and four million cases probably went unreported. Many people who have Salmonella poisoning are not aware that they have it. They do not see a doctor for treatment.
The main sources of Salmonella poisoning are egg yolks from infected chickens, raw and undercooked poultry and other meats, dairy products, fish, and shrimp. The bacterium is also found in many other foods. Egg yolks may be the most serious problem. The CDC estimates that 1 out of every 50 Americans consumes contaminated egg yolk in a year. Salmonella poisoning can be avoided by thoroughly cooking any of the foods in which it occurs. The bacteria are also found in the feces of pet reptiles, such as turtles, lizards, and snakes.
About 1 out of every 1,000 people get food poisoning from Salmonella. Of these people, two-thirds are under the age of twenty. The majority are under the age of nine. Most cases occur during the warm months between July and October.
Many methods for preserving food are available. These methods include freezing, drying, and canning. A method that may become more popular in the future is irradiation.
Irradiation is a process by which food is bombarded with high-energy radiation, such as X rays. This radiation kills bacteria in the food. Studies have shown that food irradiation is at least as effective as other methods of food preservation. For example, pork that is irradiated remains safe to eat for about ninety days. Pork kept under refrigeration is safe for no more than about forty days.
Today, the most common method for irradiating foods is with radioactive isotopes, such as cobalt 60 and cesium 137. Radioactive isotopes are materials that break apart and give off highenergy radiation.
Many people worry about the use of irradiation for preserving food. They fear that food may become radioactive and unsafe to eat. Or they worry that radiation may affect the taste, texture, or nutritional value of food.
Food irradiation is not a new technique. It has been used in other parts of the world for many years. The Food and Drug Administration (FDA) has given approval for the use of food irradiation in about a dozen kinds of foods. Whether that list becomes much longer remains to be seen.
Staphylococcus aureus occurs everywhere in the environment. It is found in dust, air, and sewage. The usual method of transmission is by food handlers who use poor sanitary practices. For example, a cook may forget to wash his or her hands after using the bathroom. Bacteria can then be transferred from the cook's hands to food. Almost any kind of food can be contaminated in this way, but some foods are especially likely to be contaminated. These foods include salad dressings, milk products, cream pastries, and any food kept at room temperature.
It is difficult to estimate the number of Staphylococcus aureus poisoning cases that occur. Most cases are quite mild, and the patient never sees a doctor.
Escherichia coli (E. coli)
E. coli is a very common bacterium. It occurs in many different strains (forms). Some forms are beneficial. They may even be essential to the normal function of our digestive systems. The strain that causes most cases of food poisoning is E. coli O157:H7. Food poisoning caused by this bacterium occurs in about 3 out of every 10,000 people. The primary sources of E. coli are foods obtained from cows, such as dairy products and beef, especially ground beef.
Campylobacter jejuni (C. jejuni)
According to the FDA, Campylobacter jejuni (pronounced KAMP-puh-lo-BAK-tur jeh-JOO-ni) is the leading cause of bacterial diarrhea in the United States. Anyone can get food poisoning from C. jejuni. However, children under the age of five and young adults between the ages of fifteen and twenty-nine are most frequently affected.
C. jejuni occurs in healthy cattle, chickens, birds, and flies. It is also found in ponds and stream water. The bacterium is very potent (powerful). Consuming no more than a few hundred C. jejuni bacteria can cause a person to become ill.
Shigella is a common cause of diarrhea in people who travel to developing countries. In these countries, sanitation practices may not be as well developed as they are in the United States. The Shigella bacterium grows well in contaminated food and water, in crowded living conditions, and in areas with poor sanitation. Shigella toxins infect the small intestine.
Clostridium botulinum (C. botulinum)
C. botulinum causes a disease known as botulism (pronounced BOTCH-u-liz-um). Two forms of botulism are known—adult and infant botulism. The C. botulinum bacterium is unlike any other bacterium in that it causes food poisoning in three ways.
First, C. botulinum is an anaerobic (pronounced AN-uh-RO-bik) bacterium. The term anaerobic means "able to live only in the absence of oxygen." That is, C. botulinum bacteria exposed to the air die quickly. Second, the toxins released by C. botulinum are neurotoxins. Neurotoxins are poisons that attack the nervous system, such as the brain and spinal cord. They may cause paralysis without producing any of the more traditional symptoms of food poisoning, such as vomiting and diarrhea. Third, botulism is a much more serious disease than other forms of food poisoning. People can die after consuming only very small amounts of the bacterium.
Adult botulism is usually caused by contaminated foods that are canned improperly at home. Less commonly, the C. botulinum bacterium is found in commercially canned foods. When foods are canned (at home or in a factory), they must first be heated to a high temperature. The temperature must be high enough to kill all C. botulinum bacteria that may be present. If the temperature is too low, some bacteria may survive. In such cases, conditions inside the can are an ideal setting for the bacteria to begin growing. No oxygen is present, and the canned food provides all the nourishment the bacteria need.