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

Abstract

Xpert MTB/RIF (Xpert) and culture are the most reliable methods for tuberculosis diagnosis but are still poorly accessible in many low-resource countries. We aimed to assess the effects of OMNIgene Sputum (OM-S) and ethanol in preserving sputum for Xpert and OM-S for mycobacterial growth indicator tube (MGIT) testing over periods of 15 and 8 days, respectively. Sputum samples were collected from newly diagnosed smear-positive patients. For Xpert, pooled samples were split into 5 aliquots: 3 for Xpert on days 0, 7, and 15 without additive and 2 with either OM-S or ethanol at day 15. For MGIT, 2 aliquots were tested without preservative and 2 with OM-S at 0 and 8 days. Totals of 48 and 47 samples were included in the analysis for Xpert and culture. With Xpert, using day 0 as a reference, untreated samples stored for 7 and 15 days showed concordances of 45/46 (97.8%) and 46/48 (95.8%). For samples preserved with OM-S or ethanol for 15 days compared with untreated samples processed at day 0 or after 15 days, OM-S concordances were 46/48 (95.8%) and 47/48 (97.9%), while those of ethanol were 44/48 (91.7%) and 45/48 (93.8%). With MGIT, concordances between untreated and OM-S-treated samples were 21/41 (51.2%) at day 0 and 21/44 (47.7%) at day 8. In conclusion, Xpert equally detected tuberculosis in OM-S-treated and untreated samples up to 15 days but showed slightly lower detection in ethanol-treated samples. Among OM-S-treated samples, MGIT positivity was significantly lower than in untreated samples at both time points.

Evaluation of Omnigene-Sputum for Preservation of Sputum Samples for Diagnosis of Mycobacterium tuberculosis

“…There are other studies evaluating the performance of OMN in different settings that use different reference methods and microbiological tests [ 2 , 3 , 10 , 12 , 18 , 19 , 20 , 21 , 22 ]. Azam et al described a good recovery of MTBC by using OMN with a high positive rate in LJ (10% in the same-day and 56% in the 5-day arms) and a low positive rate in MGIT (52% and 28% lower in the same-day and 5-day arms, respectively), but no superiority of OMN when using molecular bacterial load assay to count viable MTBC cells [ 3 ].…”