Children adopted from overseas 'could carry dormant TB'

US health experts are advising people who adopt children from overseas of the dangers of tuberculosis (TB) infection.

Scientists from the Cincinnati Children's Hospital Medical Centre told Reuters that the children may carry the dormant TB infection even if they test negative upon arriving in the US.

The researchers looked at 527 internationally adopted children and found that 20 per cent of the 191 who initially tested negative for TB were then found to be positive upon retesting.

Dr Mary Allen Staat from the hospital explained that a nine-month treatment of the drug isoniazid could clear the dormant infection and reduce the risk of a spread of TB.

"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 at least three months after their initial test," Dr Staat told the news agency.

Recent research by the University of Birmingham found that the modified gene Rv0636 can stop enzymes from "building cell walls", which controls the dehydration step of the disease.