Diagnostic performance and costs of Capilia TB for Mycobacterium tuberculosis complex identification from broth‐based culture in Bangkok, Thailand

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Abstract
Objectives Broth‐based culture (BBC) systems are increasingly being used to detect Mycobacterium tuberculosis complex (MTBC) in resource‐limited. We evaluated the performance, time to detection and cost of the Capilia TB identification test from broth cultures positive for acid‐fast bacilli (AFB) in Thailand. Methods From October–December 2007, broth cultures that grew AFB from specimens submitted by district TB clinics to the Bangkok city laboratory were tested for MTBC using Capilia TB and standard biochemical tests. Isolates that were identified as MTBC by biochemical tests but not by Capilia TB underwent repeat testing using Capilia TB, Accuprobe (Gen‐Probe, San Diego, CA, USA) and sequencing. Costs of time, labour, infrastructure and consumables for all procedures were measured. Results Of 247 isolates evaluated, the sensitivity of Capilia TB was 97% and its true specificity 100% compared with biochemical testing. The median time from specimen receipt to confirmed MTBC identification was 20 days (range 7–53 days) for Capilia TB and 45 days (range 35–79 days) for biochemical testing (P < 0.01). Six isolates that were Capilia TB negative but positive by biochemical testing were confirmed as MTBC and mutations in the mpb64 gene were detected in all. The unit cost of using Capilia TB was 2.67 USD that of biochemical testing was 8.78 USD. Conclusions In Thailand, Capilia TB had acceptable sensitivity and specificity, was lower in cost and had shorter turn‐around times. Laboratories investing in BBC should consider Capilia TB for identification of MTBC, after validation of performance in their setting.

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