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

Abstract

Abstractobjectives To assess the performance of an innovative method of transporting sputum to centralised facilities for molecular detection of Mycobacterium tuberculosis: using a swab to inoculate sputum in a transport medium, PrimeStore â Molecular Transport Medium (PS-MTM).methods Two sputum specimens were obtained from suspected patients with tuberculosis (TB) at rural healthcare facilities in South Africa. A swab was taken from each specimen and placed into PS-MTM, prior to it being processed by either liquid culture or Xpert MTB/RIF assay (Xpert).results A total of 141 patients (including 47 with laboratory-confirmed TB) were included in this analysis. M. tuberculosis was detected at 29% by culture and 29% by Xpert, whereas 31% tested positive by IS6110 real-time PCR of PS-MTM from the culture and 36% from the Xpert-paired specimen. 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, the detection rate by IS6110 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).conclusions These results suggest that swab collection of sputum into PS-MTM for transport is a promising method for diagnosis of TB in rural healthcare settings, thereby potentially improving the options available for molecular diagnosis of TB in countries incapable of applying decentralised high-tech molecular testing.

Molecular Epidemiology, Diagnostics and Mechanisms of Antibiotic Resistance inMycobacterium tuberculosiscomplex in Africa: A Systematic Review of Current Reports

“…Though the Xpert assay is preferred due to its simplicity, rapidity, higher sensitivity, ease and safety during sample processing and handling, its application in resource-limited countries is hampered by cost (5). Hence, few African countries such as South Africa has implemented Xpert assay as the baseline diagnostic method for pulmonary TB (97).…”

Preservation of sputum samples with cetylpyridinium chloride (CPC) for tuberculosis cultures and Xpert MTB/RIF in a low-income country

“…Future research should focus on the use of CPC or other preservation methods [ 18 ] for the use in liquid culture systems such as MIGT as a more sensitive culture detection and more standardized drug susceptibility testing technique than solid culture media. Moreover, addition of neutralizing buffer solutions after pretreatment with CPC to increase culture recovery warrants further exploration.…”

Molecular detection of Mycobacterium tuberculosis in poor-quality cough specimens

“…Xpert on samples collected in molecular transport medium was performed on all 65 specimens in the study, as follows: a flocked swab was swirled five times in each specimen cup (specimens not decontaminated) to collect a small quantity of sample (0.05 to 0.2 ml) for transfer into 1.5 ml PrimeStore-MTM (Longhorn Vaccines and Diagnostics, San Antonio, TX, USA). The swab in PS-MTM was vortexed for 10 s to spin captured material into the solution, the swab was removed, and the solution left to stand at room temperature for 30 min to allow for lysing of cells and the release of DNA [5]. Set-up and analysis of samples by Xpert MTB/RIF (Cepheid, USA) were performed as follows: from the PS-MTM tube, the 0.7 ml specimen was transferred into 1.4 ml of Xpert MTB/RIF sample buffer (Cepheid, 2 : 1 ratio, v/v), vortexed 10–20 times and left to stand for 15 min at room temperature with intermittent shaking [6].…”

“…tuberculosis while preserving the DNA. This molecular transport medium has been shown to destroy and inactivate the cell wall of the bacilli with the subsequent release of the DNA into the solution [5]. In addition, it allows easy transportation of specimens at ambient temperature [3].…”