Rapid detection of rifampicin susceptibility of Mycobacterium tuberculosis in sputum specimens by mycobacteriophage assay.

OBJECTIVE To evaluate the performance of FASTPlaqueTB-RIF, a newly introduced bacteriophage assay for rapid detection of rifampicin susceptibility of Mycobacterium tuberculosis in sputum specimens. METHODS A comparative study of 40 sputum specimens from patients of pulmonary tuberculosis, using FASTPlaqueTB-RIF and Bactec 460 TB system carried out at the Armed Forces Institute of Pathology, Rawalpindi between September and November 2001. RESULTS Of the 40 clinical isolates of Mycobacterium tuberculosis tested for rifampicin (RIF) susceptibility using the Bactec 460 TB system, 28 isolates were resistant to RIF and 12 isolates were susceptible. FASTPlaqueTB-RIF identified 24 specimens as resistant to RIF. Three specimens that revealed susceptible isolates on Bactec 460, were resistant by FASTPlaqueTB-RIF while four specimens which revealed resistant isolates on Bactec 460, demonstrated susceptibility to RIF by FASTPlaqueTB-RIF. The sensitivity and specificity of FASTPlaqueTB-RIF were 86% and 73% respectively. The predictive values of positive and negative tests were 0.89 and 0.67 respectively. The overall accuracy of the technique was 82%. The phage assay took 48 hours to perform. CONCLUSION Early detection of rifampicin resistance by the mycobacteriophage technique direct from sputum specimens is a potentially useful new test which would allow decision regarding appropriate therapy to be made early thus having a positive impact on patient care and on prevention of spread of MDR TB.