Microcolony culture techniques for tuberculosis diagnosis: a systematic review [Review article]

BACKGROUND: There is considerable demand for quicker and more affordable yet accurate diagnostic tools for tuberculosis (TB). The microscopic observation drug susceptibility (MODS) assay and the thin-layer agar (TLA) assay are inexpensive, rapid microcolony-based culture methods.

METHODS: A systematic review and meta-analysis was performed to assess the accuracy and other test characteristics of MODS and TLA compared to a reference standard of traditional solid or liquid culture. Pooled estimates of sensitivity and specificity and their 95% confidence intervals were estimated with an exact binomial likelihood random effects meta-analysis.

RESULTS: A total of 21 eligible studies were identified, 12 that evaluated MODS, seven that evaluated TLA and two that evaluated both. The overall pooled sensitivity and specificity of MODS were respectively 92% (95%CI 87–97) and 96% (90–100), and for TLA they were respectively 87% (95%CI 79–94) and 98% (95%CI 94–100), although there was considerable heterogeneity of results. When the studies were restricted to those assessing accuracy of MODS in sputum samples only, the sensitivity was 96% (95%CI 94–98) and the specificity 96% (95%CI 89–100). The mean intervals from reception of specimens to results were 9.2 days with MODS and 11.5 days with TLA; contamination rates averaged 6.6% with MODS and 12.3% with TLA; materials and supplies costs averaged US$1.48 for MODS and US$2.42 for TLA.

CONCLUSIONS: MODS and TLA appear to be accurate and rapid yet inexpensive diagnostic tools for active TB. However, this review did not find sufficient evidence on the feasibility and costs of implementation of these tests, nor on the impact of these tests on patient outcomes.