Scientists have found disturbing evidence that tuberculosis is making inroads among Baltimore's drug addicts -- possibly foreshadowing the resurgence here of a disease that experts hoped would soon disappear from the American scene.
Their concern comes from a study that found exceptionally high rates of positive skin tests among 260 intravenous drug users in East Baltimore. The skin test reveals if a person has been exposed to the "bug" that causes tuberculosis.
The study, a project of the Johns Hopkins School of Hygiene and Public Health, also found that the skin test is incapable of detecting exposure in many people who are infected with the AIDS virus. This is a group that is highly susceptible to developing full-blown tuberculosis once they have been exposed.
In the skin test, a nurse inserts a harmless piece of the tuberculosis bacterium under the skin.
A positive test result -- marked by a large bump where the skin was pricked -- shows that the body has already been exposed to tuberculosis and has mounted defenses against it.
* One-quarter of the addicts who did not carry the AIDS virus tested positive for TB -- compared with rates of 2 percent or 3 percent that have been seen in the general population, said Dr. Neil Graham, the epidemiologist who directed the study.
* In contrast, only 13.8 percent of the addicts who were infected with the AIDS virus reacted positively to the skin test. Dr. Graham said the true figure among these addicts, too, is probably about 25 percent. But they were less likely to respond to a skin test because the AIDS virus had weakened their bodies' defenses to the TB bacterium.
"Twenty-five percent is a ridiculously high figure," said Dr. Graham, lead author of an article in today's Journal of the American Medical Association. "You could argue that it's only intravenous drug users, but I don't think that's the case. I think there's just a lot of infection in the community."
He said drug addiction is simply a good marker for tuberculosis, which tends to thrive where people live in crowded, substandard housing: "IV drug users are very poor. They often live on the streets, thrown into homeless shelters. All the things that go into poverty place them at high risk."
Many people contract the TB bacteria without ever developing a full-blown case of tuberculosis, which is characterized by intense coughing, chest pain, shortness of breath and fever.
An otherwise healthy person stands a 10 percent chance of ever developing tuberculosis once infected with TB germs, but the AIDS virus increases the odds greatly, according to Dr. Graham.
Improved living conditions and the development of antibiotics brought about a precipitous decline in tuberculosis cases since World War II -- leading some public health experts to envision the eradication of TB in the United States early in the 21st century.
But recently, the trend has reversed. Many experts have tied the reversal to the expansion of the AIDS epidemic, along with the unrelenting problems of poverty and drug abuse.
"I think this [TB] is going to continue to be a problem, particularly among drug users who are at risk for both diseases," said Richard Dunning, chief of disease control for the Baltimore Department of Health.
In Baltimore, doctors reported 122 cases of tuberculosis in 1990.
Doctors here have yet to document particularly lethal strains of tuberculosis seen in New York -- strains resistant to antibiotics that are normally effective. But Dr. Graham said he was concerned that the New York phenomenon might simply show up in a few years in Baltimore -- mirroring the "lag" that occurred with AIDS.