Abstract
BackgroundCapilia TB is a simple immunochromatographic assay based on the detection of MPB64 antigen specifically secreted by the Mycobacterium tuberculosis complex (MTC). Capilia TB was evaluated for rapid identification of MTC from BACTEC MGIT 960 and BACTEC 9120 systems in Kampala, Uganda. Since most studies have mainly dealt with respiratory samples, the performance of Capilia TB on blood culture samples was also evaluated.MethodsOne thousand samples from pulmonary and disseminated tuberculosis (TB) suspects admitted to the JCRC clinic and the TB wards at Old Mulago hospital in Kampala, Uganda, were cultured in automated BACTEC MGIT 960 and BACTEC 9120 blood culture systems. BACTEC-positive samples were screened for purity by sub-culturing on blood agar plates. Two hundred and fifty three (253) samples with Acid fast bacilli (AFB, 174 BACTEC MGIT 960 and 79 BACTEC 9120 blood cultures) were analyzed for presence of MTC using Capilia TB and in-house PCR assays.ResultsThe overall Sensitivity, Specificity, Positive and Negative Predictive values, and Kappa statistic for Capilia TB assay for identification of MTC were 98.4%, 97.6%, 97.7%, 98.4% and 0.96, respectively. Initially, the performance of in-house PCR on BACTEC 9120 blood cultures was poor (Sensitivity, Specificity, PPV, NPV and Kappa statistic of 100%, 29.3%,7%, 100% and 0.04, respectively) but improved upon sub-culturing on solid medium (Middlebrook 7H10) to 100%, 95.6%, 98.2%, 100% and 0.98, respectively. In contrast, the Sensitivity and Specificity of Capilia TB assay was 98.4% and 97.9%, respectively, both with BACTEC blood cultures and Middlebrook 7H10 cultured samples, revealing that Capilia was better than in-house PCR for identification of MTC in blood cultures. Additionally, Capilia TB was cheaper than in-house PCR for individual samples ($2.03 vs. $12.59, respectively), and was easier to perform with a shorter turnaround time (20 min vs. 480 min, respectively).ConclusionCapilia TB assay is faster and cheaper than in-house PCR for rapid identification of MTC from BACTEC MGIT 960 and BACTEC 9120 culture systems in real-time testing of AFB positive cultures.
Highlights
Capilia TB is a simple immunochromatographic assay based on the detection of MPB64 antigen secreted by the Mycobacterium tuberculosis complex (MTC)
Performance of capilia TB for identification of MTC in BACTEC cultures In this study, the overall Sensitivity, Specificity, Positive predictive value (PPV) and Negative predictive value (NPV) of Capilia TB assay were high and in agreement with values obtained in other studies [17,20,21,24]
M. tuberculosis complex bacilli were identified in samples (51%, 129/253) by Capilia TB and in (51%, 130/253) by in-house Polymerase chain reaction (PCR)
Summary
Capilia TB is a simple immunochromatographic assay based on the detection of MPB64 antigen secreted by the Mycobacterium tuberculosis complex (MTC). A widely available diagnostic method, has low sensitivity (30% to 60%) especially in patients coinfected with HIV. Liquid culture methods are prone to contamination and usually support growth of nontuberculous mycobacteria (NTM), which may as well inhabit the upper respiratory tract and cause disease in immunocompromised patients [13]. This may lead to reporting false results especially during drug sensitivity testing in that NTM are inherently resistant to common anti-TB drugs [14,15]. MTC and NTM cause clinically different clinical symptoms prompt identification is crucial for appropriate patient management [16,17,18]
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