The single most effective way to reduce future cases of tuberculosis among the homeless is making standard treatment more available to them, according to 10-year projections based on a computer simulation.

The study found that more widespread use of existing treatment would be more effective than better treatment or vaccination.

"Recent studies showing unrecognized active TB among shelter residents and outbreaks caused by homeless individuals with long-standing untreated TB demonstrate that homeless individuals are not receiving treatment for TB in a timely fashion," says lead author Timothy F. Brewer, M.D., M.P.H., of Brigham & Women’s Hospital and Harvard Medical School.

The computer simulations conducted by the researchers indicated that a 10 percent increase in access to standard treatment would result in a 12.5 percent decrease in future active TB cases among chronically homeless people, while a 20 percent increase would produce a 23.7 percent reduction

In comparison, a 10 percent improvement in the effectiveness of treatments for active TB would produce only a 7.2 percent reduction in future cases.

The simulation indicated that TB-related deaths also would decline more with increased access to treatment compared with better treatment. A 10 percent increase in access would result in nearly a 20 percent reduction in deaths over 10 years, while a 10 percent improvement in treatment effectiveness would reduce deaths by only a little over 3 percent.

The study is published in the August 15 issue of the Journal of the American Medical Association.

TB infection often remains inactive for years or even decades, until the carrier’s immune system becomes weakened by other diseases or the aging process. Similar benefits from increased access were projected for this latent TB as well.

"A 10 percent relative increase in access to treatment of latent TB produces twice the decline in predicted TB cases and deaths in homeless persons as a 10 percent relative improvement in the effectiveness of treatment for latent TB infection," says Brewer. "Control of TB should not rely solely on strategies to increase program effectiveness."

Providing vaccination against TB in homeless persons who do not already have latent infection was also less effective than increasing access for treatment. Vaccination of 10 percent of eligible chronically homeless individuals produced a 10 percent decrease in cases and a 2.4 percent decrease in TB deaths, the model predicted.

The computer model was based on a cohort of 2 million homeless people within the general population of the United States of 1995. Of that group, 275,000 were considered to be chronically homeless and 1,725, 000 were transiently homeless. The model also accounted for migration of members of these groups between each other, into the general population and vice versa.

The study was completed with funding from the Centers for Disease Control and Prevention and the National Institute of Allergy and Infectious Diseases.

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