LARGE-SCALE USE OF POLYMERASE CHAIN-REACTION FOR DETECTION OF MYCOBACTERIUM-TUBERCULOSIS IN A ROUTINE MYCOBACTERIOLOGY LABORATORY

We investigated the use of DNA amplification by the polymerase chain r eaction (PCR) for detection of Mycobacterium tuberculosis from clinica l specimens. Two-thirds of each sample was processed for smear and cul ture by standard methods, and one-third was submitted for DNA extracti on, amplification of a 317-bp segment within the insertion element IS6 110, and detection by agarose gel electrophoresis, hybridization, or b oth. DNA was prepared from over 5,000 samples, with 623 samples being culture positive for acid-fast bacilli. Of 218 specimens that were ide ntified as M. tuberculosis, 181 (85%) were positive by PCR. In the M. tuberculosis culture-positive group, PCR was positive for 136 of 145 ( 94%) and 45 of 73 (62%) of the fluorochrome smear-positive and -negati ve specimens, respectively. Of 948 specimens that were either culture positive for mycobacteria other than M. tuberculosis or culture negati ve, 937 specimens were negative by PCR and 11 (1%) specimens initially appeared to be false positive for M. tuberculosis. The reasons for di screpant results varied; some errors were traced to the presence of an inhibitor in the specimen (7.3% in unselected specimens), nucleic aci d contamination, low numbers of organisms in the specimen, antitubercu losis therapy, and possible low-level nonspecific hybridization. In co mparison with culture, the sensitivity, specificity, and positive pred ictive value were 83.5, 99.0, and 94.2%, respectively, for PCR. When P CR was corrected for DNA contamination, the presence of inhibitor, and culture-negative disease, the values became 86.1, 99.7, and 98.4%, re spectively. If the results for multiple specimens submitted from the s ame patient are considered, no patient who had three or more sputum sp ecimens tested would have been misdiagnosed.