Diagnostic and Treatment Monitoring Potential of A Stool-Based Quantitative Polymerase Chain Reaction Assay for Pulmonary Tuberculosis

Abstract

A quantifiable, stool-based, <i>Mycobacterium tuberculosis</i> (<i>Mtb</i>) test has potential complementary value to respiratory specimens. Limit of detection (LOD) was determined by spiking control stool. Clinical test performance was evaluated in a cohort with pulmonary tuberculosis (TB) (<i>N</i> = 166) and asymptomatic household TB child contacts (<i>N</i> = 105). Stool-quantitative polymerase chain reaction (qPCR) results were compared with sputum acid-fast bacilli (AFB) microscopy, GeneXpert MTB/RIF (Xpert MTB/RIF), and cultures. In <i>Mtb</i> stool-spiking studies, the LOD was 96 colony-forming units/50 mg of stool (95% confidence interval [CI]: 84.8-105.6). Among specimens collected within 72 hours of antituberculosis treatment (ATT) initiation, stool qPCR detected 22 of 23 (95%) of culture-positive cases. Among clinically diagnosed cases that were Xpert MTB/RIF and culture negative, stool qPCR detected an additional 8% (3/37). Among asymptomatic, recently TB-exposed participants, stool PCR detected <i>Mtb</i> in two of 105 (1.9%) patients. Two months after ATT, the <i>Mtb</i> quantitative burden in femtogram per microliters decreased (Wilcoxon signed-rank <i>P</i> < 0.001) and persistent positive stool PCR was associated with treatment failure or drug resistance (relative risk 2.8, CI: 1.2-6.5; <i>P</i> = 0.012). Stool-based qPCR is a promising complementary technique to sputum-based diagnosis. It detects and quantifies low levels of stool <i>Mtb</i> DNA, thereby supporting adjunct diagnosis and treatment monitoring in pulmonary TB.