Doctors testing homeless men at a clinic in a New York City shelter have found that an extraordinarily high number are infected with tuberculosis.
Of 1,853 men who were evaluated for tuberculosis infection at the clinic from 1982 to 1988, 42.8 percent tested positive for exposure to the tuberculosis bacterium, compared with 5 to 15 percent for the population as a whole.
The study is one of the most comprehensive attempts to track tuberculosis infection among the homeless. Doctors in other cities have reported anecdotal evidence of similar infection rates in their shelters.
''The number is high; it's definitely very high,'' said Dr. Alan B. Bloch, chief of the surveillance and epidemiologic investigations branch, division of tuberculosis control at the Federal Centers for Disease Control in Atlanta. ''But it's not an entirely surprising rate of prevalence for this sort of population.''
Researchers stress that the rate of tuberculosis infection is not the same as the incidence of the disease. Of the people discussed in the new report, 6 percent had the active disease, while the remainder showed evidence that they had been exposed to the Mycobacterium tuberculosis. About 10 percent of the people exposed eventually go on to develop the illness.
The report underscores the problem of a surge in tuberculosis rates among New York's homeless, who are defined as either living in shelters or having no address.
''We're very concerned about the rates of TB among the homeless,'' said Dr. Jack Adler, medical director of the Bureau of Tuberculosis at the New York City Department of Health. ''That's why we follow people with TB through the shelter system, trying to track them and make sure they get treated.''
According to the Health Department, the number of new cases of active tuberculosis reported among the homeless rose to 240 in 1988 from 150 in 1985. In the city as a whole, there were 2,317 new cases of tuberculosis in 1988.
Alcoholism Is a Factor
The senior author of the report, Dr. John M. McAdam, attending physician at the Department of Community Medicine at St. Vincent's Hospital, attributed the high infection rate to the crowded conditions of the shelter and to the rise in AIDS, which by compromising the immune system invites secondary infections like tuberculosis.
Other experts add that alcoholism, which is common among some homeless people, also increases the risk of tuberculosis infection.
The men studied in the new report, which appears in this month's issue of Chest, a cardiopulmonary journal, had attended the clinic associated with the Charles H. Gay Shelter Care Center for Men on Wards Island, either to receive treatment for other medical complaints or to have physical examinations required by the city's work programs.
''It's not an entirely representative sample of the homeless population,'' Dr. McAdam said. ''These are men who came to a clinic for other reasons. Many of them already were sick, so the rate of TB infection could be expected to be high in this case.''
But Dr. McAdam said the findings highlighted the need to identify and treat all tuberculosis victims in the shelters as quickly as possible. Only those with the active form of the ailment can spread the infection, by coughing and releasing the bacteria in airborne water molecules of the proper size and electric charge to infiltrate the lungs of another person.
''Shelters, with their confined conditions, are likely places for the disease to spread,'' he said.
But Dr. Adler insisted that it was still ''an open question'' whether shelters promote the transmission of tuberculosis. He noted that many people who enter the shelter system have many risk factors for the disease.
''You're selecting out a population that already has a high rate of infection because of alcoholism, AIDS infection and so forth,'' he said. ''Does it spread further still in the shelters? We're still looking into that.''
Dr. McAdam agreed that the question was difficult to resolve and required that a stable population of the homeless be repeatedly examined for infection over several years.
A Troubling Pattern
The men that he and his colleagues studied were examined or tested for tuberculosis only once each, using a scratch skin test.
Tuberculosis rates throughout the nation have shown a troubling pattern of resurgence. After dropping by 5 to 7 percent a year from about 1950 to 1982, the decrease flattened. From 1985 to 1989 there were more than 20,000 cases beyond what experts would expect if the decline had continued. ''AIDS and homelessness account for a large part of the excess cases,'' Dr. Bloch said.
Tuberculosis is readily cured by a combination of two or three antibiotics although treatment takes six to nine months.