Tuberculosis has an uncanny ability to ensure its own spread and survival. It oftens fools doctors and patients into thinking it is a cold, the flu or bronchitis.
By the time the symptoms--fatigue, loss of appetite, night sweats and the hacking cough most people associate with TB--are correctly diagnosed, others may have been infected, by breathing the bacteria expelled every time the patient coughed or sneezed.
The rod-shaped bacteria, mycobacterium tuberculosis , is minuscule (the average speck of dust is 50 times larger), which makes it ideal for penetrating the innermost reaches of the lungs, though anywhere in the body is susceptible. Pulmonary tuberculosis, which is marked by that terrible cough, occurs in 85% of all patients.
The disease spreads most easily through closed dwellings with little sunlight and poor air circulation--hospital wards, prisons, crowded apartment buildings. Yet TB is not easy to catch. "You have to generally come within a couple of feet of a person who is actively coughing and you usually need to be in that position on a fairly regular basis," says Dr. Gerard Frank, a pulmonary specialist at White Memorial Medical Center in East Los Angeles. And deaths among people who have a regular strain of TB and have treated it are rare. (However, drug-resistant forms of TB are highly fatal.) Nonetheless, according to the latest figures available from the Centers for Disease Control, of 25,701 cases, 1,760 people died in 1990.
Ninety percent of the infected people never even get sick. An estimated one-third of the world's population harbors the TB germ; in most, the body keeps the germ in check.
An estimated 5% of those infected develop active tuberculosis within two years of infection, and another 5% become ill sometime during their lives, generally when their immune systems are weakened by other illnesses or physical stress.
A simple injection of a tiny amount of extracted TB bacteria tells doctors who has the germ and who does not. To confirm an active TB diagnosis, X-rays are taken and sputum samples are tested.
For patients under age 35 who test positive but do not have active tuberculosis, doctors generally recommend six to 12 months of preventive treatment with isoniazid, also known as INH, an anti-tuberculosis drug that mutates the germ. For people over 35 with no other complications, preventive treatment is not recommended.
Active tuberculosis patients require a more complicated drug regimen, often involving three or four medications and lasting six months in most cases or as long as two years in rare cases. The treatment usually renders the disease non-infectious within a matter of days.
However, some patients don't finish taking their medication. And it is these patients who worry public-health authorities most, because they are the ones most likely to develop deadly strains of drug-resistant TB--and to spread them.