Abstract
BackgroundEven though the WHO-endorsed, non-commercial MODS assay offers rapid, reliable TB liquid culture and phenotypic drug susceptibility testing (DST) at lower cost than any other diagnostic, uptake has been patchy. In part this reflects misperceptions about in-house assay quality assurance, but user convenience of one-stop procurement is also important. A commercial MODS kit was developed by Hardy Diagnostics (Santa Maria, CA, USA) with PATH (Seattle, WA, USA) to facilitate procurement, simplify procedures through readymade media, and enhance safety with a sealing silicone plate lid. Here we report the results from a large-scale field evaluation of the MODS kit in a government service laboratory.Methods & Findings2446 sputum samples were cultured in parallel in Lowenstein-Jensen (LJ), conventional MODS and in the MODS kit. MODS kit DST was compared with conventional MODS (direct) DST and proportion method (indirect) DST. 778 samples (31.8%) were Mycobacterium tuberculosis culture-positive. Compared to conventional MODS the sensitivity, specificity, positive, and negative predictive values (95% confidence intervals) of the MODS Kit were 99.3% (98.3–99.8%), 98.3% (97.5–98.8%), 95.8% (94.0–97.1%), and 99.7% (99.3–99.9%). Median (interquartile ranges) time to culture-positivity (and rifampicin and isoniazid DST) was 10 (9–13) days for conventional MODS and 8.5 (7–11) for MODS Kit (p<0.01). Direct rifampicin and isoniazid DST in MODS kit was almost universally concordant with conventional MODS (97.9% agreement, 665/679 evaluable samples) and reference indirect DST (97.9% agreement, 687/702 evaluable samples).ConclusionsMODS kit delivers performance indistinguishable from conventional MODS and offers a convenient, affordable alternative with enhanced safety from the sealing silicone lid. The availability in the marketplace of this platform, which conforms to European standards (CE-marked), readily repurposed for second-line DST in the near future, provides a fresh opportunity for improving equity of access to TB diagnosis and first and second-line DST in settings where the need is greatest.
Highlights
Global control of tuberculosis (TB) and multidrug resistant tuberculosis (MDRTB) is hindered by a lack of access to affordable and reliable diagnostic tests in the countries with the greatest need
A further 21 (2.7%) additional samples were positive by both microscopic-observation drug-susceptibility (MODS) Kit method and LJ culture, but not by the conventional MODS assay. 1603 (65.5%) were culture negative by all three methods, and 65 samples (2.7%) were contaminated by at least one method, without a parallel positive culture
Of the 87 samples that were positive by LJ and/ or MODS Kit, but negative by conventional MODS, one third of samples (n = 29) were classified as ‘‘indeterminate’’ in the parallel conventional MODS assay on first processing and all but one were negative after reprocessing and repeat culture performed according to the protocol
Summary
Global control of tuberculosis (TB) and multidrug resistant tuberculosis (MDRTB) is hindered by a lack of access to affordable and reliable diagnostic tests in the countries with the greatest need. The microscopic-observation drug-susceptibility (MODS) assay, developed in Peru [2,3,4] is a highly sensitive and specific phenotypic diagnostic test for TB and MDRTB This low-cost, non-commercial assay is well suited to resource-constrained settings and was endorsed by the WHO in 2010 [5]. The procurement by laboratory staff of reagents and consumables from multiple providers can be challenging, and settings with a high burden of TB tend to be those more commonly afflicted by limited human and economic resources and unreliable supply chains due to inadequate infrastructure, weak administrative procedures, conflict and/or natural disaster [7] In these circumstances mechanisms to simplify procurement, such as the availability of an ‘‘off the shelf’’ kit that requires interaction with only a single supplier, have appeal. We report the results from a large-scale field evaluation of the MODS kit in a government service laboratory
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