Rapid diagnosis of active pulmonary tuberculosis in children by amplicor mycobacterium tuberculosis PCR test

ABSTRACT

Conventional diagnosis of Mycobacterium tuberculosis by culture generally takes 3 to 8 weeks. Acid fast smears lack sensitivity and can not distinguish M. tuberculosis from other mycobacteria. Rapid differentiation of M. tuberculosis from other mycobacteria species is therefore of great potential benefit. The PCR can provide a rapid and specific identification of M. tuberculosis complex organisms. The reliability of the Roche AMPLICOR Mycobacterium tuberculosis test [AMPLICOR MTB] for the diagnosis of active pulmonary tuberculosis in children was evaluated by testing 204 specimens [sputum, early morning gastric aspirates, and tracheobronchial lavage] which employs a fast and simplified sample preparation method appropriate for routine diagnostic testing. The specimens were taken from 86 children who were suspected of having active pulmonary MTB on the basis of the presence of one or more of the following criteria [1] positive tuberculin skin test, [2] abnormal chest radiograph consistent with tuberculosis and/or [3] history of exposure to an adult with infectious tuberculosis. In order to evaluate the accuracy of the PCR assay, PCR results were compared with culture, staining techniques and medical history. Of these 204 specimens, 35 were culture positive for M. tuberculosis from 24 patients. 27 specimens were smear positive for acid fast bacteria [AFB]. On initial testing, the sensitivity and specificity of the AMPLICOR MTB assay, compared with culture, were 88.6% and 98.2% respectively. After resolution of discrepancies [by review of medical history], the sensitivity, specificity, and positive and negative predictive values of the AMPLICOR MTB assay were 89.2%, 99.4%, 97.1%, and 97.6%, respectively. One specimen was AMPLICOR MTB positive and culture positive for Mycobacterium avium complex. For AFB smear-positive specimens, the sensitivity, specificity, and positive and negative predictive values of AMPLICOR MTB were 96.4%, 100%, 100%, and 50%, respectively. For AFB smear-negative specimens, the sensitivity, specificity, and positive and negative predictive values of AMPLICOR MTB were 66.7%, 99.4%, 85.7% and 97.6%, respectively. Our results support the use of AMPLICOR MTB for rapid diagnosis of tuberculosis in children whose respiratory specimens are AFB smear positive. Further studies are needed to determine the most clinically relevant and cost-effective use of this assay with AFB smear-negative specimens