New Test Allows Early Detection of Tuberculosis Infection

LONDON (Reuters Health) Jun 21 - A new antigen-specific T cell-based assay may allow earlier detection of tuberculosis infection than the currently used tuberculin skin test (TST), according to a report published in the June 23rd issue of The Lancet.

The test, known as the ESAT-6 enzyme-linked immunospot (ELISPOT) assay, detects T cells specific to an antigen secreted by Mycobacterium tuberculosis, the authors state.

Dr. Ajit Lalvani, from the University of Oxford, in the UK, and colleagues compared the efficacy of the ELISPOT assay with TST in detecting M. tuberculosis infection in a group of 50 asymptomatic subjects with varying degrees of exposure to the bacterium.

The ELISPOT results showed a strong positive correlation with the intensity of exposure, while the TST results showed a much weaker association, the researchers note. Prior BCG vaccination had no bearing on the ELISPOT results, but did increase the likelihood of a positive TST result.

"The strong positive relation between ESAT-6 ELISPOT results and M. tuberculosis exposure, and the lack of relation with BCG vaccination status, allow symptomless M. tuberculosis infection to be distinguished from BCG vaccination, thereby avoiding unnecessary chemoprophylaxis in uninfected individuals," the authors note.

Dr. Lalvani's team believes that the new "assay has the potential to be used to identify recently infected contacts and other individuals at high risk of M. tuberculosis infection in low prevalence countries, which would enable accurate tracking of M. tuberculosis transmission in outbreaks, improved targeting of chemoprophylaxis, and should facilitate epidemiologic studies of M. tuberculosis transmission."

Lancet 2001;357:2017-2021.