Investigation of OMNIgene·SPUTUM performance in delayed tuberculosis testing by smear, culture, and Xpert MTB/RIF assays in Uganda

Abstract

OMNIgene·SPUTUM (OM-S) is a sample transport reagent designed to work with all tuberculosis diagnostics while eliminating the need for cold chain. OM-S-treated sputum samples were assayed in several tests after multiday holds. Raw sputa from 100 patients underwent direct smear microscopy, were manually split and assigned to the OM-S group [OM-S added at collection (no other processing required) and tested after 0- to 5-day holds at room temperature] or standard-of-care (SOC) group (NaOH/N-acetyl l-cysteine decontamination, all tested on day of collection). Concentrated smear microscopy, Lowenstein Jensen (LJ) culture, and mycobacteria growth indicator tube (MGIT) culture were performed. For patients with negative direct smear, a second sample was split, with SOC (raw sputum) and OM-S portions (sediment) tested in the Xpert MTB/RIF (Xpert) assay. OM-S group and SOC group results were strongly concordant on all four tests [range, 89% (MGIT)-97% (Xpert)]. OM-S MGIT, LJ, and Xpert tests were in statistical agreement with SOC MGIT as reference. OM-S specimens had lower culture contamination rates (3% vs. 10% LJ; 2% vs. 5% MGIT) but required, on average, 5.6 additional days to become MGIT-positive. The findings suggest that samples held/transported in OM-S are compatible with smear microscopy, LJ or MGIT culture, and Xpert, and perform comparably to fresh sputum samples. Larger feasibility studies are warranted.

Keywords: MGIT; Molecular detection; Mycobacterium tuberculosis; Preservation; Solid culture; Specimen transport medium.

Fig. 1.

Schematic of the study protocol for sample collection, treatments, and testing. Each patient’s initial sputum sample (Sputum 1) was split manually, the two specimens received either standard-of-care (SOC) or OMNIgene·SPUTUM (OM-S) treatment, and each specimen was then tested by concentrated fluorescent microscopy and solid and liquid culture. If the direct smear from Sputum 1 was negative, the patient also provided a second sputum sample (Sputum 2), which was divided and treated identically to Sputum 1. The SOC specimen was then Xpert-tested using Cepheid’s Raw Sputum protocol. The OM-S specimen was centrifuged to produce a sediment following manufacturer instructions, and was tested using Cepheid’s Concentrated Sputum protocol. CFM = concentrated fluorescent microscopy; DFM = direct fluorescent microscopy; LJ = Lowenstein Jensen; MGIT = mycobacteria growth indicator tube; OM-S = OMNIgene·SPUTUM; SR = Sample Reagent.