Diseases of the Respiratory System - Tuberculosis
At the turn of the century tuberculosis was the leading cause of death in the world; now it is eighteenth. The change in status is due both to the discovery of antibiotics and to modern preventive measures. In this century most other infectious diseases have likewise decreased in incidence and severity for similar reasons. The general decline leaves tuberculosis still at the top of the list as the leading cause of death among infectious diseases. And tuberculosis remains a very serious health problem, accounting for 40,000 new illnesses every year in the United States. In contrast to a disease like influenza, physicians already have the tools with which to eliminate tuberculosis. But many factors, primarily social, make that a very distant possibility.
Tuberculosis is caused by one specific type of bacterium. Certain ethnic groups seem particularly susceptible to the disease, but the reasons are unclear. The American Indian and the Eskimo are two susceptible groups. However, there is no recognized hereditary factor. The disease is different from many commonly known infections in several ways. Unlike pneumonia, tuberculosis is a chronic and painless infection, measured more in months than in days. Because of this pattern, it not only takes a long time to develop serious disease, but it also takes a long time to effect a cure.
Another very important difference between tuberculosis and many other infections is its ability to infect individuals without causing symptoms of illness, but then to lie dormant as a potential threat to that person for the rest of his life. The early stages of the disease do not produce any symptoms. Consequently a patient develops large areas of diseased tissue before he begins to feel sick. Screening procedures, therefore, are very important in detecting early disease in patients who feel perfectly healthy. Another is the skin testing of schoolchildren, which is carried out routinely in many communities today.
How Tuberculosis Spreads
Tuberculosis is contracted by inhaling into the lungs bacteria that have been coughed into the air by a person with advanced disease. It is, therefore, contagious, but not as contagious as measles, mumps, or chicken pox. Unlike those illnesses, it usually requires fairly close and prolonged contact with a tuberculous patient before the infection is passed on. Once the bacteria are inhaled, the body defenses are usually capable of isolating them into small areas within the tissues, thereby preventing any significant destruction or disease. However, though defenses are able to isolate the bacteria, they are not able to destroy all of them. Some bacteria persist in a state in which they are unable to break out and destroy tissue, but they always maintain the potential to do so at a time when the body defenses are impaired.
In about 20 percent of individuals the body defenses are not initially capable of isolating the tubercle bacilli. These individuals, mostly children, develop progressive tuberculosis directly following their initial contact. Others are successful in preventing actual disease at the time of initial contact, but they join a large group with the potential for active disease at some time in the future. Most of the new cases of active tuberculosis come from this second group; their defenses break down years after the initial contact and resultant infection.
Weight loss, malnutrition, alcoholism, diabetes, and certain other chronic illnesses are particularly likely to lead to deterioration of the defense mechanisms holding the tuberculosis organisms in check. Still other individuals develop active disease with no recognizable condition to account for the loss of defenses. In fact, the most likely age group to develop active disease as a result of breakdown of past infection is the 20- to 30-year-old group.
Once active disease has appeared it usually involves the chest, although it can develop anywhere in the body. There is gradual spread of inflammation within lung tissue until large areas are involved. Holes, or cavities, are formed as a result of tissue destruction. These contain large numbers of tuberculosis organisms and continue to enlarge as new tissue is destroyed at the edges. At any stage of this development organisms may find their way into the bloodstream and new foci of disease can spring up throughout the body. The sputum becomes loaded with organisms that are coughed into the air and go on to infect other individuals. The infected sputum from one area of the lung may gain access to other areas and cause development of diseased tissue there as well.
Before the modern era of drug treatment all these events followed an inexorable course to death in 85 percent of people with active tuberculosis. Only a lucky few were able to survive as cured, usually because their disease was found at an early stage. That survival was often at the expense of years confined to a sanatorium. Because of its almost uniform outcome and the required separation from family and home, tuberculosis was formerly looked upon with quite as much dread as cancer is today.
The sanatorium rest cure of tuberculosis was first developed in the mid-nineteenth century at a time when the cause of the disease was unknown. In 1882, Robert Koch first demonstrated the tuberculosis organism, thereby proving the disease was an infection. As the twentieth century progressed, general public health measures helped limit the number of new cases, and new surgical procedures were developed to treat the disease. These measures were effective enough to arrest tuberculosis in another 25 percent of cases, brightening somewhat the dismal outlook of the past century.
But the discovery of specific antibiotics in the 1940s made the real difference in tuberculosis. Because of drug treatment, surgery is rarely resorted to today, although it still may be helpful in certain patients. Now patients with tuberculosis can face a relatively bright future without having to be hospitalized for prolonged periods or enduring periods of endless disability.
People still contract tuberculosis, and people still die from it. Two of the principal causes of death are delayed therapy and interruptions in therapy, the latter leading to the development of tuberculosis organisms that are unaffected by drugs. Both of these causes are often under the control of the patient. The first can be avoided by seeing a physician whenever one develops a cough that lasts more than two weeks, especially when it is not associated with the typical symptoms of a cold at the outset. The other symptoms of developing tuberculosis are also seen in other illnesses, and should always lead one to recognize that he is sick and needs to consult his physician. These symptoms are weight loss, loss of appetite, fever, and night sweats. When tuberculosis is diagnosed, the patient must follow carefully the directions regarding medication, which is always continued for a long time after the patient has regained his feeling of well-being.
There are other ways, however, to attack tuberculosis, even before one becomes sick. Once a person has had contact with tuberculosis, even though he usually does not develop active disease, he produces antibodies against the bacteria. A person with such antibodies can be recognized by injecting under the skin specially prepared material from dead tuberculosis bacteria, which gives rise to a reaction within the skin after two days. This material is called tuberculin and the test is known as the tuberculin test .
There are now many mass screening programs of tuberculin testing for schoolchildren, hospital personnel, and industrial groups. Those with positive skin test reactions are screened further for the presence of active disease. If they are found to be active cases, they are treated during what is usually an early and not very severe stage of the disease. The other people with positive tuberculin tests, without any evidence of active disease, are candidates for prophylactic (preventive) therapy . This therapy employs isoniazid ( INH ), the most effective of many drugs for the treatment of tuberculosis. INH does have many possible side effects. Treatment for six months to one year has been shown to reduce greatly the chance of future progress from the merely infected state to the state of active disease.
The goal of prophylactic therapy is chiefly to prevent the far more serious development of active disease. But in addition, by preventing disease before it develops, physicians can prevent the infection of others, since the typical patient with tuberculosis has already infected some of those living with him before he becomes ill and seeks medical attention. The surface has just been scratched in this regard, however, as there are estimated to be 25 million people in the United States who would demonstrate reactions to tuberculin tests. Many of these people have never been tested and are not aware of the potential threat within them.
In most foreign countries the tuberculosis problem is much more serious. An estimated 80 percent of the populations of the countries of Asia, Africa, and South America would show positive tuberculin skin tests, with the number of active cases and deaths being proportionately high.