Combining the Capilia TB Assay with Smear Morphology for the Identification of Mycobacterium Tuberculosis Complex

Setting: Many hospitals in Taiwan use the fully automated BACTEC Mycobacterial Growth Indicator Tube (MGIT) 960 system to identify mycobacteria in clinical specimens, while the labour-intensive BD ProbeTec ET (CTB) system or biochemical methods are used to identify Mycobacterium tuberculosis complex (MTC) in mycobacterially positive BACTEC cultures.

Objective: To evaluate whether the Capilia TB assay can be used to replace the BD ProbeTec ET (CTB) system or biochemical methods for identifying MTC in BACTEC cultures.

Design: Mycobacterially positive BACTEC cultures were collected and MTC in the cultures was identified using biochemical methods. MTC was identified using serpentine cording in smears, the Capilia TB assay or the BD ProbeTec ET (CTB) system, and the results were compared.

Results: Using 233 mycobacterially positive BACTEC cultures, the sensitivity and specificity of identification of the Capilia TB assay were respectively 96.9% and 98.6%, while those of the BD ProbeTec ET (CTB) system were respectively 99.4% and 97.3%. Combining the Capilia TB assay with serpentine cording in smears led to 100% specificity for intersected results and 100% sensitivity for combined results.

Conclusion: The Capilia TB assay can be used to identify MTC in BACTEC cultures. By combining the assay with serpentine cording in smears, false-positives and -negatives may be reduced.