Field evaluation of a novel preservation medium to transport sputum specimens for molecular detection of Mycobacterium tuberculosis in a rural African setting

Abstract

Molecular tests are revolutionizing diagnosis of tuberculosis (TB). Disease burden is concentrated in resource-poor countries with inadequate infrastructure and capacity resulting in delays for specimens to reach the laboratory. We assessed the performance of an innovative method using a swab to inoculate sputum in a transport medium, PrimeStore® - Molecular Transport Medium (PS-MTM) for subsequent molecular detection of Mycobacterium tuberculosis at a centralized facility. A sputum specimen was obtained from suspected TB patients at rural healthcare facilities in South Africa and a swab taken and placed into PS-MTM from this specimen, prior to it being processed by either liquid culture or Xpert MTB/Rif assay (Xpert). A subset from a larger cohort study of a 141 patients was included for analysis, which included 47 laboratory-confirmed TB patients. M. tuberculosis was detected at 29% by culture, 29% by Xpert and 31% and 36% by real-time PCR of PS-MTM for the culture and Xpert specimen respectively. Concordance between the method under evaluation with culture was 82% (McNemar, p=0.55) and 84% (McNemar, p=0.05) for Xpert. Stratified by culture result, detection rate by real-time PCR of PS-MTM was similar to Xpert for patients with positive culture (p=0.32), but significantly higher if culture was negative (p=0.008). These results suggest that swab collection of sputum into PS-MTM provides a promising application for diagnosis of TB in rural healthcare settings thereby potentially improving the options available for the diagnosis of TB in countries incapable of applying decentralized high-tech molecular testing.