Immigrants with TB pose no public health risk

By Michael Kahn

LONDON (Reuters) - Immigrants with tuberculosis are not likely to spread the disease in their new countries and pose no public health threat, Norwegian researchers said on Thursday.

The study of TB cases in Norway over a 12-year period found little evidence to support concerns that immigrants from poor countries where the airborne disease is rampant may transmit infection to the wider population when they move.

"Immigrants do not threaten non-immigrants," said Ulf Dahle, a microbiologist at the Norwegian Institute of Public Health, who led the study.

TB is a sometimes fatal bacterial infection usually attacking the lungs. Each year the disease kills 2 million people -- about 5,000 a day -- mostly in the developing world, according to the World Health Organization.

Earlier this year an American lawyer, Andrew Speaker, triggered an international health alert and raised fears about the disease crossing borders when he flew from Europe with a hard-to-treat type of tuberculosis.

Antibiotics do not work against some strains, and there are fears that immigrants from poor countries will transmit this stubborn form of the disease in their new homes.

But the Norwegian team said while the number of cases went up because many immigrants had TB, the new arrivals did not raise the risk of contagion.

"We didn't see any increase in the transmission in the TB," Dahle said in a telephone interview.

While the bacteria that spread tuberculosis can be carried through the air, experts agree it usually takes close contact lasting at least several hours to transmit the infection.

In the study published in the American Journal of Respiratory and Critical Care Medicine, the researchers studied the 2,173 known cases of TB in Norway between 1993 and 2005.

They tracked outbreaks among native Norwegians and immigrants to determine the genetic strain of each confirmed case. The team determined the genetic diversity of the strains was 87 percent, which indicates very limited transmission.

"Had there been more extensive transmission within the country, we would have seen a greater degree of similarity between infecting strains," Dahle said.

The reason is that immigrants often keep within their own groups and, more importantly, Norway has programs in place to quickly diagnose and treat outbreaks, he said.

The findings also suggest other Western countries with similar controls do not have spikes in transmission when immigrants from TB hotspots arrive, Dahle said.

"(The findings) should aid TB control and eradication programs and reduce the fear of imported outbreaks," he said.