http://www.reutershealth.com/archive/2002/05/08/eline/links/20020508elin001.html

Latent TB found to be more common in US immigrants

Last Updated: 2002-05-08 16:52:40 -0400 (Reuters Health)

By Merritt McKinney

NEW YORK (Reuters Health) - New study findings may help to explain why the large drop in tuberculosis (TB) cases that occurred in the US during the last decade was limited mostly to people born in the US, and did not affect foreign-born US residents.

In contrast to US-born residents with TB, whose disease most often resulted from recent infection with the TB bacterium, foreign-born residents were more likely to become sick after a dormant TB infection became active, according to a review of TB cases in New York City.

Because recent public health efforts to control TB have focused on treating newly-infected cases of the disease rather than preventing dormant cases from becoming active, the findings suggest that providing TB screening and preventive treatment to recent immigrants may lead to greater declines in TB cases in the US, Dr. Neil W. Schluger at Columbia University in New York told Reuters Health in an interview.

Public health programs have focused on treating people who have been recently infected with TB, according to Schluger, who is the lead author of a report on the findings in the May 9th issue of The New England Journal of Medicine.

"That's a very effective way to prevent the spread from one person to another," he said. But "what it doesn't do is prevent cases among people who have already been infected" but whose tuberculosis has been dormant.

He explained that some people who are exposed to TB bacteria become infected, but the organisms lie dormant in the body. These people are healthy, they do not feel sick and they cannot transmit TB to others, Schluger said. But about 10% of people with dormant TB eventually develop active disease.

Schluger and his colleagues used a new DNA "fingerprinting" technique to analyze more than 500 TB cases that occurred in several New York City neighborhoods, including Washington Heights, an area in northern Manhattan where more than 40% of residents were born outside the US.

Based on the DNA fingerprints, the researchers estimated that 48% of TB cases were caused by recent infections and 52% resulted from reactivation of a latent infection. Compared to US-born residents with TB, people born in other countries were 49% to 69% less likely to have become ill from a recently acquired strain of TB, according to the report.

The only exceptions were foreign-born residents infected with HIV, the virus that causes AIDS, who were more likely to become ill from a recently contracted infection, the report indicates.

The results suggest that most transmission of TB in the US occurs among people born in this country, according to Schluger. He noted that TB is most often spread by drug users, homeless people, and those with HIV. Efforts at treating these cases of TB have resulted in a substantial decline in TB cases. To achieve further declines, it will be necessary to provide screening and treatment to immigrants to eliminate latent infections, he said.

Unfortunately, Schluger said, the treatment for eliminating dormant TB infection--an antibiotic plus a vitamin--must be taken daily for 9 months. "What we really need," he said, is a treatment that is "much shorter and more effective."

Indeed, a "serious research effort" is needed to develop better therapy or a vaccine for dormant or persistent TB, according to Dr. Barry R. Bloom at the Harvard School of Public Health in Boston, Massachusetts. But the campaign against TB must be a global one that aims to control TB in developing nations, he notes in an accompanying editorial.

"It would be the most effective public health action we could take to protect people in our country from tuberculosis," Bloom writes.

Schluger agreed that a global approach is needed to defeat TB, stressing, "We can't think of TB as a problem only in our country."

SOURCE: The New England Journal of Medicine 2002;346:1434-1435, 1453-1458.

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