Molecular detection and identification of mycobacterium tuberculosis complex and four clinically important nontuberculous mycobacterial species in smear-negative clinical samples by the genotype mycobacteria direct test.

Although the sensitivity and specificity of nucleic acid amplification assays are high with smear-positive samples, the sensitivity with smear-negative and extrapulmonary samples for the diagnosis of tuberculosis in suspicious tuberculosis cases still remains to be investigated. This study evaluates the performance of the GenoType Mycobacteria Direct (GTMD) test for rapid molecular detection and identification of the Mycobacterium tuberculosis complex and four clinically important nontuberculous mycobacteria (M. avium, M. intracellulare, M. kansasii, and M. malmoense) in smear-negative samples. A total of 1,570 samples (1,103 bronchial aspiration, 127 sputum, and 340 extrapulmonary samples) were analyzed. When we evaluated the performance criteria in combination with a positive culture result and/or the clinical outcome of the patients, the overall sensitivity, specificity, and positive and negative predictive values were found to be 62.4, 99.5, 95.9, and 93.9%, respectively, whereas they were 63.2, 99.4, 95.7, and 92.8%, respectively, for pulmonary samples and 52.9, 100, 100, and 97.6%, respectively, for extrapulmonary samples. Among the culture-positive samples which had Mycobacterium species detectable by the GTMD test, three samples were identified to be M. intracellulare and one sample was identified to be M. avium. However, five M. intracellulare samples and an M. kansasii sample could not be identified by the molecular test and were found to be negative. The GTMD test has been a reliable, practical, and easy tool for rapid diagnosis of smear-negative pulmonary and extrapulmonary tuberculosis so that effective precautions may be taken and appropriate treatment may be initiated. However, the low sensitivity level should be considered in the differentiation of suspected tuberculosis and some other clinical condition until the culture result is found to be negative and a true picture of the clinical outcome is obtained.