Magnetic bead flocculation test: Improving the diagnosis of tuberculous meningitis (TBM) in low-resource settings

Background Despite several recent advances in detection techniques, there is still an unmet need for simple tests for the diagnosis of tuberculous meningitis (TBM). Therefore, in an effort towards developing a simple and rapid diagnostic test for resource-poor settings, we designed an assay in which magnetic bead flocculation test (MBF) was used to detect the amplified DNA. Multi-targeted (using two multicopy gene targets IS6110 and IS1081) loop-mediated isothermal amplification (MLAMP) was used for amplification. Methods MLAMP-MBF assay was performed on CSF samples of 600 patients, out of which 120 were definite TBM (culture confirmed), 280 were probable TBM and 200 were non-TB controls, based on Marais's criteria. The performance of assay was evaluated by comparing the result of definite TBM with culture and that of probable TBM with composite reference standard consisting of clinical, microbiological(smear/culture) and radiological parameters. Results The overall sensitivity of MLAMP-MBF (using any of the two gene targets) was 89.5% and specificity was 100%. The sensitivity was 96.6% (116/120) in diagnosing definite TBM and 86.4% (242/280) in diagnosing probable TBM. The sensitivity of IS1081 was 88% and that of IS6110 was 83% in diagnosing TBM. Specificity of both the gene targets was 100%. There were 20 cases positive only by IS1081 LAMP and 6 cases positive only by IS6110; thus 26 of 400 (6.5%) TBM cases could be additionally detected following multi-targeted approach. Conclusion MLAMP-MBF is a sensitive, robust, cost-effective and promising technique for diagnosis of TBM in low-resource high-endemic settings.