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 2001-06. Their findings are being published in Wednesday'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."

Of those infected, drug-resistant TB was found in 20 percent of recent immigrants from Vietnam and 10 percent of foreign-born residents overall, compared with a little more than 4 percent of U.S.-born residents.

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 attorney 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. He said the study helps identify which foreign-born groups would be most appropriate for such an effort.

While most TB cases come from recent arrivals, a significant number involve people who have lived in the United States for at least 20 years, the study authors said. Most of these likely resulted from latent infections acquired years earlier abroad, they wrote.

Latent, non-contagious 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 and their immune systems weaken.

Latent infections are detected with skin tests and treated with nine months of antibiotics. Foreign-born U.S. residents aren't routinely tested for latent TB. And with more than 37 million foreign-born people living in the United States, giving all of them skin tests "would be daunting to say the least," Cain said.

JAMA: http://jama.ama-assn.org

CDC: http://www.cdc.gov