Clinical evaluation of the mycobacteriophage-based assay in rapid detection of Mycobacterium tuberculosis in respiratory specimens.

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.