CHICAGO - Tuberculosis cases continue to fall in the United States, but some immigrants have disturbingly high rates of the disease, according to a study released Tuesday that called for more aggressive action.

TB rates were highest among residents from lower Africa and parts of Southeast Asia. Most drug-resistant TB cases also were from foreign-born residents, the study noted.

The researchers called for wider testing, including efforts to seek out latent cases of TB from long-term immigrant residents in certain populations.

Rates of at least 250 TB cases per 100,000 were found among people from African countries such as Ethiopia, Kenya and Somalia and from Southeast Asian nations including Vietnam, Cambodia and the Philippines.

By comparison, the overall rate of TB in the U.S. is fewer than 5 per 100,000, according to researchers at the Centers of Disease Control and Prevention, whose study is based on data from 2001 to 2006. The findings are being published in today's Journal of the American Medical Association.

Dr. Henry Blumberg of Emory University's medical school, said the research shows "that it's in the interest of the United States to try to enhance global TB efforts."

Public health officials worry that drug-resistant TB could become a worldwide scourge because of global travel and immigration. The issue made headlines last year when an Atlanta lawyer with drug-resistant TB flew to several countries. Tests later showed he did not infect anyone on those flights.

U.S. law requires TB screening for people who want to immigrate to the United States, said the CDC's Dr. Kevin Cain, the study's lead author.

Another step that would help curb the rise of tuberculosis, he said, would be to find and treat latent TB infections.

Latent, noncontagious infections mean germs are present but the body is able to fight off symptoms. Latent infections can morph into active disease, causing contagious illness, at any time, particularly as people age.