tuberculosis

Tuberculosis is a disease caused by infection with Mycobacterium tuberculosis. In the past it was a common disease; in this century it has been if not conquered, at least contained very effectively in the developed world. Now, the advent of HIV threatens to bring this rightfully feared infection back into new prominence.

Tuberculosis is a disease of person-to-person contact. People with active lung infection shed infectious droplets, which are inhaled by close contacts. The disease becomes established first in the lungs. Most infectious patients discharge relatively few organisms, so casual contacts have a low risk of infection. Most transmission of the disease is to household members, schoolmates, or other close contacts. TB is more common in immigrants, in situations where there is crowding and poverty (especially homelessness), or a high risk of HIV infection. HIV infected patients are 100 to 200 times more likely to have TB.

Much confusion can arise in the minds of worried parents who receive the news that their child has a "positive TB skin test." A positive TB skin test does not by itself prove there is active disease but does indicate that infection has occurred and is harbored within the body. It does not establish whether or not the patient is infectious.

In children, the diagnosis of tuberculosis is most often made when the child is skin-tested as part of a contact-surveillance program initiated by the local health department when an adult with whom the child has had some contact is diagnosed with the disease. Children may initially become ill with serious disseminated disease or tuberculous menigititis, but these cases are rare.

Patients may have different stages of the disease:

A TB converter is a person who has been exposed to the disease and harbors it in the body; the TB test turns positive. but the immune system has contained the infection. Clinical illness does not develop and this person is not contagious.
A few patients (perhaps 5%) fail to fight off the initial exposure in this way, and progress to active infection within the first two years after exposure. These patients are indeed contagious.
Another 5% of infected patients develop a reactivation of the previously contained and dormant infection, most often within 2 to 4 years of the initial infection or at times of stress and lowered resistance. They start shedding the bacillus in their sputum and are contagious.
Reactivation of old, dormant infection can occur many decades after initial infection. Most "new" cases are actually reactivated TB acquired years earlier. Thus, children often contract TB from an elderly grandparent whose disease reactivates with the decline of the immune system in old age.

Some cases of tuberculosis in children are eventually determined to be atypical mycobacterial infections. Atypical mycobacteria are naturally occurring germs in the soil. These infections are probably acquired from inhalation or ingestion of organisms from normal outdoor play. There is no evidence for person-to-person transmission. One classic presentation of atypical TB in childhood is cervical lymphadenitis (scrofula).

In many parts of the world where tuberculosis is common, bacille Calmette-Guerin (BCG) vaccine is used for the prevention of primary infection. It is not be given to patients with positive skin tests. Because the incidence of tuberculosis is relatively low in the United States, BCG is not routinely recommended in this country. Close contacts of patients with active pulmonary tuberculosis should be considered for protective isoniazid (INH) therapy, particularly if they are children, adolescents, nursing home residents, or immunocompromised individuals.

The mainstay of TB management of newly converting skin test positive individuals remains isoniazid (INH), usually given daily for about six months. Patients with a positive skin test are evaluated to exclude active infection; besides physical examination, a chest xray is very important. If they have no evidence of active infection, prophylaxis with INH is considered. The drug has numerous potential side effects, including skin rash, fever, fatigue, anorexia, abdominal distress, jaundice, or peripheral nerve damage. A physician who specializes in TB management will weigh and discuss the risks versus the benefits of prophylactic treatment, and monitor for side effects once treatment is instituted. All cases of tuberculosis must be reported promptly to public health authorities, so that contacts can be tested and given prophylaxis if necessary, and any actively infectious cases in the community can be discovered and treated.

Patients with active tuberculosis require aggressive treatment. They usually receive multidrug regimens for several weeks in the hospital until they are non-contagious, followed by six to nine months or longer of outpatient treatment.

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