Accuracy of the phenotypic 1G test to detect Mycobacterium tuberculosis and drug resistance from sputa in the US-Mexico border

TL;DR

A new low-complexity test for tuberculosis detection and drug resistance shows high accuracy and faster results than traditional methods.

Contribution

The 1G test offers a practical, low-complexity alternative to culture-based TB diagnostics with high sensitivity and specificity.

Findings

The 1G test detected Mtb with ≥98% sensitivity and had high specificity for drug resistance testing.

The 1G test had lower contamination rates and a 17-day time to detection compared to MGIT's 21 days.

The study site had a 14% drug-resistant TB prevalence when testing all participants, higher than passive reporting.

Abstract

With >10 million new tuberculosis (TB) cases/year, a limitation to TB control is the lack of simple and accurate tests for TB diagnosis and drug-susceptibility testing (DST) in endemic regions. We evaluated the accuracy of the first-generation, low-complexity phenotypic TB test (1G test), designed for simultaneous Mtb detection and resistance to isoniazid, rifampicin and moxifloxacin, suitable for resource-limited settings.

A cross-sectional study was conducted using sputa from 426 possible pulmonary TB subjects from two small Mexican cities bordering Texas. The 1G test was compared against phenotypic TB detection tests in the region [acid fast bacilli smear microscopy and Mycobacteria Growth Indicator Tube (MGIT) culture], and to MGIT-DST for resistance to isoniazid, rifampicin and moxifloxacin.

The 1G test demonstrated ≥98% sensitivity for Mtb detection, 100% sensitivity and 91% (rifampicin), 94% (isoniazid) and 97% (moxifloxacin) specificity for DST, and less contamination than the MGIT (3.5% vs. 8.1%; p<0.05). The 1G test time to detection (TTD) of Mtb and simultaneous DST was 17-days, while the MGIT-DST required two steps: 7 days for Mtb detection plus 14 more (total 21 days) for DST. Our study site DR-TB prevalence was 14% when testing all consecutively-enrolled participants vs. 6% by passive reporting.

The 1G test is a low-complexity phenotypic TB diagnostic method that is a practical replacement to current culture-based tests. Future studies are warranted to evaluate the implementation of the 1G test in decentralized clinics that lack molecular tools, resources and expertise.

The 1G test, a low-complexity phenotypic assay, detected Mycobacterium tuberculosis and drug resistance with high accuracy, low contamination and within 21 days, offering an affordable option for decentralized TB diagnosis and drug susceptibility testing, where molecular tools are not subsidized.

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