Evaluation of the FASTPlaqueTB assay for direct detection of Mycobacterium tuberculosis in sputum specimens.

SETTING Sputum samples were collected from suspected tuberculosis patients attending out-patient clinics at the Ojha Institute of Chest Diseases, Karachi, Pakistan. OBJECTIVE To evaluate the performance of the FASTPlaqueTB assay for rapid diagnosis of pulmonary tuberculosis. DESIGN A comparative study of 584 sputum samples using acid-fast smear microscopy, Lowenstein-Jensen culture and FASTPlaqueTB. RESULTS A total of 514 samples yielded complete results. Seventy specimens were lost to analysis due to the overgrowth of contaminants. The addition of antimicrobials inhibited growth of gram-positive contaminants, and reduced the overall contamination rate from 18.2% to 7.2%. Mycobacterium tuberculosis was isolated from 175 smear-positive and 70 smear-negative specimens. FASTPlaqueTB detected M. tuberculosis in 81.6% of specimens, with a specificity of 97.7%. The sensitivity and specificity of the assay for smear-positive specimens were respectively 87.4% and 88.2%. For smear-negative specimens, the sensitivity of the assay was 67.1% and the specificity was 98.4%. The combined sensitivity of smear and FASTPlaqueTB for M. tuberculosis was 90%. Test results were available in 48 hours. CONCLUSION FASTPlaqueTB is a sensitive and specific test for rapid diagnosis of pulmonary tuberculosis in high prevalence areas. The test is sensitive enough to confirm a large number of clinically suspected smear-negative cases and improve case finding.