Contact tracing using a new T-cell-based test: better correlation with tuberculosis exposure than the tuberculin skin test.
METHODS
Residential institution for alcoholics in Switzerland.


OBJECTIVE
To compare the results of the tuberculin skin test (TST) and the new T-cell-based test for tuberculosis infection (T-SPOT.TB) in subjects exposed to a case of smear-positive pulmonary TB (PTB).


METHODS
After the notification of smear-positive PTB in a resident of an institution for alcoholics, contacts underwent TST and determination of Mycobacterium tuberculosis specific T-cells in blood by T-SPOT.TB. Results were analysed according to age, history of BCG vaccination, and level of exposure to the index case.


RESULTS
There was no correlation between the level of exposure and the TST results, but the T-SPOT.TB results were significantly correlated with the level of exposure (P = 0.029, OR 5.00, 95%CI 1.05-23.86). Contacts who had been previously BCG-vaccinated were significantly more likely to have a positive TST than unvaccinated contacts (52% vs. 0%, P = 0.0003), but there was no influence of prior BCG vaccination on T-SPOT.TB results.


CONCLUSIONS
T-SPOT.TB test results correlated better than TST with level of exposure to M. tuberculosis and were not confounded by prior BCG vaccination. This test allows better selection of contacts who should receive treatment for latent TB infection.
Zellweger
J-P
JP
University Medical Outpatient Department, Bugnon 44, 1011 Lausanne, Switzerland. zellwegerjp@swissonline.ch
Zellweger
A
A
Ansermet
S
S
de Senarclens
B
B
Wrighton-Smith
P
P
D000328:Adult; D000368:Aged; D016358:Contact Tracing / Q000379:methods*; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D013601:T-Lymphocytes / Q000276:immunology; D014374:Tuberculin Test; D014397:Tuberculosis, Pulmonary / Q000097:blood / Q000175:diagnosis* / Q000635:transmission*