The results of the study, to be published in a special June 8 theme issue on tuberculosis in the Journal of the American Medical Association, mean that switching to the more expensive blood test may not be necessary for people in India.
"Our study is the first time this blood test has been evaluated in India, where TB is highly endemic," said Dr. Madhukar Pai, a post-doctoral fellow in epidemiology at UC Berkeley's School of Public Health and lead author of the paper. "It's also the largest study of its kind among health care workers, a group that is at high risk for occupational TB."
There are about 9 million new cases of TB each year, and a large proportion of the disease burden is in developing countries. Most people infected with TB contain the infection, and it remains latent. In some individuals, the infection progresses to active disease.
The tuberculin skin test, in which the skin is pricked with antigens from Mycobacterium tuberculosis, had stood alone for more than 100 years as the method for detecting latent TB infection.
However, many health professionals consider the skin test crude, said Pai, because it is unable to clearly distinguish between people who have received a vaccine against TB from those who have a true infection. Moreover, the skin test requires the patient to return three days after the skin prick so that a health worker can measure the resulting bump on the skin.
Having a test that allows health care officials to confirm a true TB infection is important because a positive test can lead to a six-month treatment of daily anti-TB drugs for the patient.