EVALUATION OF AMPLICOR MTB TEST AS ADJUNCT TO SMEARS AND CULTURE FOR DIRECT-DETECTION OF MYCOBACTERIUM-TUBERCULOSIS IN THE FRENCH CARIBBEAN

A total of 784 specimens collected from 370 individuals between Januar y and August 1995 were analyzed by using the Amplicor Mycobacterium tu berculosis test (Roche Diagnostic Systems, Basel, Switzerland), a PCR- based test for the direct detection of organisms of the M. tuberculosi s complex. The PCR results were compared with standard bacteriological data, including those obtained by acid-fast microscopy, culture, and biochemical identification as well as final clinical diagnosis for eac h patient, Several parallel controls were used: the kit DNA positive c ontrol, 10(3) CFU of M. tuberculosis, and three negative controls for each independent assay, No false-positive PCR results were obtained, a nd overall, M. tuberculosis was detected in 20 of 370 individuals scre ened. Five additional patients during the same time were found to be i nfected with mycobacteria other than tubercle bacilli; their specimens gave positive smear and/or culture test results, but Amplicor tests w ere always negative. The sensitivity, specificity, positive predictive value, and negative predictive value for the Amplicor MTB test compar ed with culture per specimen were 76.7, 97.7, 66.0, and 98.6%, respect ively. For resolved cases, these values were, respectively, 69.4, 100, 100, and 96.8%; however, the sensitivity and negative predictive valu e increased to 90.9 and 99.2%, respectively, if PCR-negative nonrespir atory specimens (gastric washings) were not considered. When only spec imens from proven tuberculosis patients were considered (n = 114) and the sum of PCR-positive and/or culture-positive samples from proven tu berculosis patients was considered the total number of positive sample s, PCR had a sensitivity of 83.3% compared with 71.6% for culture. Res ults per patient (about three samples each) yielded 100% sensitivity a nd 100% specificity. We conclude that the Amplicor MTB test is highly specific and rapid for routine use in a clinical laboratory. However, in order to obtain a high degree of sensitivity, it should be run as a n adjunct to smears and culture with at least three samples for each p atient, and a single-sample PCR-negative result must be considered car efully because of potential false-negatives.