Performance and Cost-Efficiency of an MPT64 Assay for Detecting Mycobacterium tuberculosis Complex in a Setting With Frequent Nontuberculous Mycobacteria Isolation

초록

Background: Rapid and accurate detection of Mycobacterium tuberculosis complex (MTBC) in acid-fast bacilli (AFB)-positive cultures is crucial for effective patient management and transmission control. This study assessed the diagnostic performance and cost-efficiency of the Bioline MPT64 assay for detecting MTBC in AFB-positive cultures in a setting with frequent nontuberculous mycobacteria (NTM) isolation. Methods: Between August 2024 and February 2025, AFB-positive cultures were tested in parallel using the Bioline MPT64 assay and real-time polymerase chain reaction (PCR). The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the Bioline MPT64 assay were calculated using real-time PCR as the reference standard. Cost-efficiency of diagnostic strategies incorporating the Bioline MPT64 assay was also evaluated. Results: Based on real-time PCR results, among 494 AFB-positive cultures, 192 (38.9%) were MTBC-positive, 299 (60.5%) were NTM-positive, 2 (0.4%) were positive for both MTBC and NTM, and 1 (0.2%) was negative for both. The Bioline MPT64 assay exhibited a sensitivity of 99.0% (192/194), specificity of 100% (300/300), PPV of 100% (192/192), and NPV of 99.3% (300/302). Two false-negative results occurred in MTBC-NTM co-positive cultures. Using the Bioline MPT64 assay alone could reduce costs by 66.7% compared to real-time PCR alone but carries a risk of missing approximately 1.0% of MTBC-positive cultures. A stepwise strategy-initial screening with the Bioline MPT64 assay followed by real-time PCR for MPT64-negative cultures-could offer diagnostic accuracy comparable to real-time PCR alone but result in only a modest 5.5% cost reduction. Conclusion: The Bioline MPT64 assay shows strong concordance with real-time PCR and offers substantial cost savings when used alone, though it may miss MTBC-NTM co-positive cultures. PCR confirmation of MPT64-negative results mitigates this risk but provides only modest cost savings in NTM-prevalent settings.

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