Evaluation of Mycobacterium tuberculosis viability in OMNIgene-SPUTUM reagent upon multi-day transport at ambient temperature

Abstract

BackgroundMaintaining the quality of clinical specimens for tuberculosis (TB) testing is a major challenge in many high TB burden-limited resources countries. Sample referral systems in low and middle income countries are often weak and the maintenance of the cold-chain challenging and very costly for TB programs. The development of transport media allowing the preservation of samples without refrigeration is critical for increasing access to TB diagnostic services and for reducing the costs related to testing.MethodsWe evaluated the performance of OMNIgene-SPUTUM (OM-S) reagent for the maintenance of Mycobacterium tuberculosis (MTB) viability in sputum samples in the absence of refrigeration and its capacity to stabilize nucleic acid for molecular testing. A total of 329 sputum specimens from presumptive TB cases collected at the National Reference Laboratory in Tirana, Albania, were either decontaminated by a conventional method or processed with OM-S reagent and stored at room temperature. Samples in OM-S were shipped to the Supranational Reference Laboratory in Milan, Italy, at various times and processed for liquid culture.ResultsOur data show that OM-S maintains MTB viability for at least three weeks in the absence of refrigeration and improves the quality of culture resulting in a contamination rate lower than 0.5%. However, a significant delay in the time to culture positivity was observed for samples stored for more than two weeks in OM-S.ConclusionsOverall, OM-S offers multiple benefits both at laboratory and TB national program level by increasing the availability to quality diagnostics, promoting access to health care services and strengthening TB patient care especially in hard to reach populations.

Evaluation of OMNIgene Sputum and Ethanol Reagent for Preservation of Sputum Prior to Xpert and Culture Testing in Uganda

“…There was only one contaminant on untreated samples at day 0. Previous studies have shown that OM-S-treated samples have a lower contamination rate than untreated counterparts (10,(12)(13)(14)(15)23). In our study, only one contaminant in the untreated group may not explain much about the contribution of OM-S in reducing contamination compared to standard decontamination.…”

“…Finally, we observed a substantial delay in days to positivity between untreated and OM-S-treated samples at both time points. Previous studies have also noted delayed culture growth in samples treated with OM-S (13,15,21,22). This raises further concerns about the utility of OM-S in its current procedure and the compatibility with MGIT cultures.…”

“…One study reported poor recovery of MTC across both MGIT and Lowenstein-Jensen (LJ) media (13). One study reported improved results in MGIT cultures using samples treated with OM-S for up to 3 weeks, with the only concerns being about a delay in MGIT results (15).…”

“…OM-S has the ability to liquefy and decontaminate samples at the same time, offering the possibility to extend their storage until 8 days at temperatures up to 40°C prior to culture inoculation (8). However, studies investigating the effect of OM-S have shown good accuracy but mainly with Lowenstein-Jensen (LJ) culture (10,11), while those using MGIT have reported contrasting results (12)(13)(14)(15).…”

Evaluation of OMNIgene®•SPUTUM reagent for mycobacterial culture

“…8 The mycobacterial cell wall with its thick and relatively impermeable layer of mycolic acid has 9 unique characteristics. The complexity of the cell wall represents a challenge to the organism, 10 requiring specialized mechanisms to allow cell division to occur and resulting in prolonged 11 generation times compared to gram-positive or -negative bacteria. 4 Respiratory samples are 12 therefore specially treated, a process called 'decontamination' before inoculation and incubation 13 of broth and solid media.…”