Utility of nucleic acid amplification techniques for the diagnosis of pulmonary tuberculosis in sub-Saharan Africa

SETTING: Lusaka, Zambia. OBJECTIVES: To investigate the utility of nucleic amplification tests for t he diagnosis of pulmonary tuberculosis in a resource-poor setting with a hi gh incidence of human immunodeficiency virus (HIV). DESIGN: Sputum specimens from suspects attending a referral chest clinic we re examined by low-cost 'in-house' one-tube nested polymerase chain reactio n (PCR), the enhanced Gen-Probe Amplified Mycobacterium Direct Test (AMTD), auramine smear and Lowenstein-Jensen culture. RESULTS: PCR and AMTD detected respectively 80% and 92% of smear-positive s pecimens and 30% and 60% of smear-negative, culture-positive specimens. AMT D was positive for 18 culture-negative suspects; subsequent investigation i ndicated these to be six confirmed tuberculosis patients, nine judged from radiological data and clinical follow-up studies to have pulmonary tubercul osis, and three non-tuberculosis patients. Sensitivity for smear, culture, PCR and AM-TD, when compared to a gold standard incorporating both microbio logical and clinical data, was respectively 29%, 69%, 55% and 81%. CONCLUSION: In this setting, the sensitivity of the low-cost PCR proved ins ufficient for its effective use as a tool for diagnosing pulmonary tubercul osis, while AMTD performed considerably better than the current laboratory methods for diagnosis of pulmonary tuberculosis. However, the high cost of this technology may limit its application in the public sector of low-incom e countries.