ABSTRACT
SETTING: Mbeya, Tanzania. OBJECTIVE: To develop a new liquid culture method to detect Mycobacterium tuberculosis complex (MTC) in sputum using 2,3-diphenyl-5-thienyl-(2)-tetrazolium (STC), the nitrate reductase assay (NRA) and p-nitrobenzoic acid (PNB). DESIGN: Ninety-three sputum samples collected from 18 tuberculosis patients were decontaminated with N-acetyl-L-cysteine-sodium hydroxide using MGIT™ 960 and in STC-NRA cultures, both in the presence and in the absence of PNB, an inhibitor of MTC growth. The reduction of STC by colour change indicated mycobacterial growth; NRA was then performed to confirm MTC. RESULTS: STC-NRA culture was positive for acid-fast bacilli in 66/93 (71%) samples, of which 60/93 (64.5%) were identified as MTC-positive and 6/93 (6.5%) as indeterminate mycobacteria. MGIT indicated MTC in 59/93 (63.4%) cultures. Contamination was detected in 12/93 (13%) STC-NRA cultures vs. 29/93 (31.2%) MGIT cultures. The mean time to detection (TTD) of MTC using STC-NRA was 14 days and 7 days using MGIT. CONCLUSION: The STC-NRA method is sensitive for the detection of MTC in sputum. TTD increased with duration of anti-tuberculosis treatment, highlighting the value of this method in monitoring treatment success. The method is simple and inexpensive and, unlike MGIT, does not require technical equipment. The preliminary performance characteristics of the method should be further evaluated in larger studies.
Subject(s)
Colorimetry/methods , Mycobacterium tuberculosis/isolation & purification , Sputum/microbiology , Tuberculosis, Pulmonary/diagnosis , Antitubercular Agents/therapeutic use , Drug Monitoring/methods , Feasibility Studies , Humans , Mycobacterium tuberculosis/drug effects , Mycobacterium tuberculosis/growth & development , Predictive Value of Tests , Tanzania , Time Factors , Treatment Outcome , Tuberculosis, Pulmonary/drug therapy , Tuberculosis, Pulmonary/microbiologyABSTRACT
In this pilot study, we evaluated the Xpert® MTB/RIF assay in an active case-finding strategy, using two spot sputum samples collected within a 1-hour interval from household contacts of smear-positive TB index cases. Tuberculosis (TB) confirmed by culture served as the reference standard. Among 219 enrolled contacts, the yield of active TB was 2.3%. While the sensitivity of smear microscopy was 60% (95%CI 14.7-94.7), Xpert MTB/RIF achieved a sensitivity of 100% (95%CI 47.81-100.0). All culture-confirmed cases tested positive by Xpert MTB/RIF on the first submitted sample, suggesting that the evaluation of only one sample could be sufficient for TB diagnosis in this context.
