Performance of a Highly Sensitive Mycobacterium tuberculosis Complex Real-Time PCR Assay for Diagnosis of Pulmonary Tuberculosis in a Low-Prevalence Setting: a Prospective Intervention Study

Abstract

The potential impact of routine real-time PCR testing of respiratory specimens from patients with presumptive tuberculosis in terms of diagnostic accuracy and time to tuberculosis treatment inception in low-prevalence settings remains largely unexplored. We conducted a prospective intervention cohort study. Respiratory specimens from 1,020 patients were examined by acid-fast bacillus smear microscopy, tested by a real-time Mycobacterium tuberculosis complex PCR assay (Abbott RealTime MTB PCR), and cultured in mycobacterial media. Seventeen patients tested positive by PCR (5 were acid-fast bacillus smear positive and 12 acid-fast bacillus smear negative), and Mycobacterium tuberculosis was recovered from cultures for 12 of them. Patients testing positive by PCR and negative by culture (n = 5) were treated and deemed to have responded to antituberculosis therapy. There were no PCR-negative/culture-positive cases, and none of the patients testing positive for nontuberculous mycobacteria (n = 20) yielded a positive PCR result. The data indicated that routine testing of respiratory specimens from patients with presumptive tuberculosis by the RealTime MTB PCR assay improves the tuberculosis diagnostic yield and may reduce the time to antituberculosis treatment initiation. On the basis of our data, we propose a novel mycobacterial laboratory algorithm for tuberculosis diagnosis.

Keywords: Mycobacterium tuberculosis; acid-fast bacillus smear microscopy; mycobacterial culture; nontuberculous mycobacteria; real-time PCR.

FIG 1

Diagram of the proposed laboratory workflow strategy for the diagnosis of tuberculosis and nontuberculous mycobacterial lung infections. Respiratory specimens from patients with suspected TB are first examined by AFB smear microscopy. AFB smear-positive specimens are processed for mycobacterial culture. All specimens (irrespective of AFB smear results) are tested by the Abbott real-time PCR assay (or any other NAAT assay with equivalent sensitivity). Positive MTC PCR specimens are cultured on Löwenstein-Jensen medium slant LJ and MGIT (Mycobacterium growth indicator tube) to confirm the infecting species strain conservation and typing and phenotypic drug susceptibility testing (DST) results. Negative PCR specimens are discarded unless derived from patients with a high level of clinical and radiological suspicion of NTM lung disease (targeted laboratory test ordering).