CLINICAL EVALUATION OF THE MYCOBACTERIOPHAGE-BASED ASSAY IN RAPID DETECTION OF MYCOBACTERIUM TUBERCULOSIS IN RESPIRATORY SPECIMENS

Abstract

Context: Search for a cost-effective, rapid and accurate test has renewed interest in mycobacteriophage as a tool in the diagnosis of tuberculosis (TB). There has been no reported data on the performance of phage assay in a high burden, low-resource setting like Kanpur city, India. Aims: To assess the sensitivity and specificity of the FASTPlaque TB™ kit ability to impact the bacillary load in the phage assay and its performance in the sputum smear sample negative cases. Materials and Methods: The study involved a cross-sectional blinded assessment of phage assay using the FASTPlaque TB™ kit on 68 suspected cases of pulmonary TB against sputum smear microscopy by Ziehl-Neilsen staining and culture by the LJ method. Results: The sensitivity, specificity and positive and negative predictive values of the phage assay were 90.7, 96, 97.5 and 85.7%, respectively. The assay was negative in all the five specimens growing mycobacteria other than TB. The sensitivity of the phage assay tended to decrease with the bacillary load. Of the smear-negative cases, three were false negative, and all of which were detected by the phage assay. Smear microscopy (three smears per patient) had a sensitivity and specificity of 93 and 64%, respectively. Conclusions: The phage assay has the potential clinical utility as a simple means of rapid and accurate detection of live Mycobacterium tuberculosis bacilli; however, its performance has been inconsistent across various studies, which highlights that the assay requires a high degree of quality control demanding infrastructure and its performance is vulnerable to common adversities observed in “out of research” practice settings like storage, transport and cross-contamination.