Dr. Kevin P. Cain of the Centers for Disease Control and Prevention in Atlanta examined the 46,970 cases of TB disease reported from 2001 to 2006 among foreign-born people in the United States.

The study, published in the Journal of the American Medical Association, found 12,928 cases, or 28 percent, were among those in the United States less than two years. Among the foreign-born population overall, TB case rates declined with increasing time since U.S. entry, but remained about four times higher than among U.S.-born persons -- even 20 years after arrival.

Among recent entrants culture-positive for TB, resistance to the antibacterial drug used to treat TB -- isoniazid -- was found in 20 percent from Vietnam, 18 percent from Peru, 17 percent from the Philippines and 16 percent from China.

Individuals born in most countries of sub-Saharan Africa had annual case rates of greater than 250 per 100,000 persons during the first two years after U.S. entry, while individuals born in Central America, Eastern Europe, the Pacific Islands, and Southeast and Central Asia had annual case rates of greater than 100 per 100,000 persons.