Molecular detection of Mycobacterium tuberculosis: Impact on patient care

Background: Nucleic acid amplification technologies such as PCR are revolut ionizing the detection of infectious pathogens such as tuberculosis (TB). A mplification technology offers the potential for the diagnosis of TB in a f ew hours with a high degree of sensitivity and. specificity. However, molec ular assays neither replace nor reduce the need for conventional smear and culture, speciation, and antibiotic sensitivity assays. Methods: We undertook prospective studies of sputum samples to assess the p erformance of two PCR-based assays for the detection of TB as well as the i mpact of more rapid availability of test results on patient care. Results: The sensitivity of both the in-house and Amplicor PCR assays was 1 00% for smear-positive sputa: For smear-negative sputa (two sputum samples collected during the first 24 h of hospitalization), the sensitivity was 85 % for our in-house PCR assay and 74% for the Roche PCR assay. Approximately 10% of the smear- and culture-negative sputa yielded positive PCR results; however, more than one-half of these were positive with both the in-house and Amplicor assays; suggesting the presence of TB DNA or organisms: Severa l of these came from patients whose other samples grew Mycobacterium tuberc ulosis during the same admission, and others came from patients who had pre viously treated TB. Overall, the specificities of the in-house and Amplicor PCR assays in smear-negative patients were 86% and 93%, respectively. Conclusions: Molecular detection of slow-growing pathogens such as M. tuber culosis have the potential to, improve clinical care through a dramatic red uction in the time required for detection and may provide substantial savin gs in the overall cost of care of a patient compared with conventional smea r, culture, and speciation alone, despite the fact that conventional assays must still be performed for speciation of nontuberculous mycobacteria and for full assessment of antibiotic sensitivity. (C) 2001 American Associatio n for Clinical Chemistry.