Objective: To compare the enzyme-linked immunospot (ELISPOT) assay with the tuberculin skin test (TST) in children for the diagnosis of Mycobacterium tuberculosis infection in the Gambia.
Methods: We divided child contacts of sputum smear-positive tuberculosis cases into 3 age categories (<5, 5-9, and 10-14 years) and assessed agreement between the 2 tests plus their relationship to prior Bacille Calmette-Guerin (BCG) vaccination. We categorized a child's level of M tuberculosis exposure according to where he/she slept relative to a case: the same room, same house, or a different house. The relationship between exposure and test result was assessed by multiple logistic regression.
Results: In child contacts of 287 cases, 225 (32.5%) of 693 were positive by TST and 232 (32.3%) of 718 by ELISPOT. The overall agreement between tests was 83% and the discordance was not significant. Both tests responded to the M tuberculosis exposure gradient in each age category. The percentage of those who were TST positive/ELISPOT negative increased with increasing exposure. At the lowest exposure level, the percentage of ELISPOT-positive children who were TST negative was increased compared with the highest exposure level. Neither test had evidence of false positive results because of BCG.
Conclusions: In Gambian children, the ELISPOT is slightly less sensitive than the TST in the diagnosis of M tuberculosis infection from recent exposure, and neither test is confounded by prior BCG vaccination. Evidence of reduced TST sensitivity in subjects with the lowest known recent M tuberculosis exposure suggests that, when maximal sensitivity is important, the 2 tests may be best used together.