Children adopted from overseas may harbor tuberculosis infection even if they test negative for TB upon arriving on US soil, a new report warns.

"It's important to get that repeat tuberculosis skin test done so you don't miss those children with TB infection that could go on to develop disease," Dr. Mary Allen Staat of the Cincinnati Children's Hospital Medical Center told Reuters Health.

People with latent (dormant) TB infection, she explained, are not sick and are not contagious, and treatment with a nine-month course of isoniazid will usually clear the infection. But once infection progresses to active disease, a person may become ill and can spread the disease to others. At this point, treatment is much more complex, requiring as many as four drugs.

The American Academy of Pediatrics recommends that all children adopted from countries where TB is endemic be tested soon after they arrive in the US, and suggests that children who test negative be retested later on if they are malnourished, Staat and her team point out in an article in Pediatrics this month. However, they also point out that no specific evidence justifying this recommendation has been published.

To investigate whether repeat testing would spot more children with TB infection, the researchers looked at 527 internationally adopted children treated at their International Adoption Center. Twenty-one percent tested positive for latent TB infection. The researchers were able to perform repeat tests in just under half of the 191 children who had tested negative initially, and 20 percent of these children tested positive upon retesting.

There are many reasons why a child might test negative for TB initially, Staat said. Some children may be too malnourished to mount an appropriate immune response to the test, while others may have been infected shortly before leaving their country of origin. It can take 2 to 12 weeks after being exposed to TB for a person to test positive for infection.

Staat and colleagues say "guidelines for the care of internationally adopted children should include recommendations for retesting all internationally adopted children with an initially negative tuberculin skin test result, not just those considered malnourished, at least three months after their initial test."