Foreigners account for nearly 60 percent of all tuberculosis patients in New York City, but it is not because immigrants are bringing in new cases — it is because old infections are resurfacing, a study finds.
The reason appears to be that a campaign against the disease focused on treating new, active cases instead of eliminating latent infections, Elvin Geng, a medical student at Columbia University, reported in Thursday's New England Journal of Medicine.
Scientists at Columbia and the New York City Health Department looked at 546 cases in Manhattan's Washington Heights neighborhood from 1990 to 1999. Washington Heights has a large population of Dominicans and other immigrants.
Using DNA analysis to determine which cases had been recently transmitted, Geng found that the percentage caused by recent transmission fell from 63 percent in 1993 to 31 percent in 1999.
In most people, the immune system blocks TB bacteria, but the germs can break out years, even decades, later.
The recommended treatment for people most at risk for developing TB from these latent infections is nine months of medication.
The World Health Organization estimates that one-third of the world's 6.2 billion people are infected with TB, but only 5 percent to 10 percent of them become ill.
The National Institute of Allergies and Infectious Diseases estimates that 10 million to 15 million U.S. residents have such latent infections, and about one in 10 of them will eventually develop active TB.
On the Net: World Health Organization TB links: www.who.int/health-topics/tb.htm
TB Fact sheet: www.niaid.nih.gov/factsheets/tb.htm