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Stopping the Spread of Tuberculosis

Study recommends screening new immigrants from developing nations

THURSDAY, Dec. 5, 2002 (HealthDayNews) -- Screening and treating new immigrants from developing nations for the latent stage of tuberculosis would produce substantial public health benefits, a new study from Toronto suggests.

Targeting the treatment to take into account global differences in patterns of antibiotic resistance is also crucial, says study author Dr. Kamran Khan, a clinician-scientist at St. Michael's Hospital at the University of Toronto. The report appears in today's issue of The New England Journal of Medicine.

Tuberculosis (TB), an infectious and potentially life-threatening bacterial infection, kills about 2 million people a year, according to the World Health Organization (WHO). Antibiotics are used to treat the active disease. Globally, the TB epidemic is becoming more dangerous, and differences in antibiotic resistance patterns from region to region are complicating efforts to contain the disease, experts say.

Khan's team constructed a decision-analysis mathematical model, using statistics from the U.S. Centers for Disease Control and Prevention (CDC) and other sources and also plugging in region-specific drug resistance profiles.

Khan explains the focus on immigrants. "The reason we conducted the study was that in the United States and other industrialized countries, including Canada and much of Western Europe, we see a growing proportion of all TB cases among immigrants. In Toronto, for instance, 90 percent of all TB cases are [in] foreign-born. In Australia, it's 80 percent."

"Our study found screening and treating immigrants for what we call latent-stage TB would result in substantial public health and economic benefits," he says.

"TB can exist in two stages, latent infection and active, sometimes called active disease," Khan says. "If a normal immune system is exposed [to TB], the body would contain the infection and keep it in the latent stage. There would be no symptoms, and it would not be transmissible." However, if the immune system is weakened -- by contracting HIV, for instance -- that can trigger active disease.

Finding and treating those with latent disease, the study found, can reduce their risk of developing active disease by about 70 percent. Screening all immigrants for latent disease for a year would prevent up to 10,000 future cases of active disease, the model predicts, and would save between $60 million and $90 million in costs to society.

Khan's team also took into account the antibiotic resistance that has developed in different geographic regions and makes recommendations about regimens. For instance, rifampin and pyrazinamide is the preferred drug combination for those originally from Vietnam, Haiti and the Philippines.

Khan acknowledges the rifampin-pyrazinamide regimen should be closely monitored, because of reports of severe and fatal liver injuries, which prompted a CDC public health dispatch last month.

Another expert, Dr. Peter Katona, an assistant professor of medicine at the David Geffen School of Medicine at the University of California, Los Angeles, applauds the study. "Their idea to screen [for latent infection] is a very good idea," he says.

Containing TB infections in immigrants can only boost public health, he adds. A single TB infection, if active, can infect numerous other persons, he says. According to the WHO, each person with active TB who is not treated will infect at least 10 more persons a year.

"So it is definitely cost-effective [to screen and treat] for public health," Katona says.

What To Do

For more information on tuberculosis, see the World Health Organization. For more information on guidelines for rifampin and pyrazinamide, see the U.S. Centers for Disease Control and Prevention.

SOURCES: Kamran Khan, M.D., M.P.H.,, specialist, infectious disease and public health, and clinician-scientist, St. Michael's Hospital, Inner City Health Research Unit, Toronto; Peter Katona, M.D., assistant professor, medicine, David Geffen School of Medicine, University of California, Los Angeles; Dec. 5, 2002, The New England Journal of Medicine
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