Clinical diagnostic performance of the simultaneous amplification and testing methods for detection of the Mycobacterium tuberculosis complex for smear-negative or sputum-scarce pulmonary tuberculosis in China

Abstract

Background: Early detection of pulmonary tuberculosis (PTB) is a big challenge in smear negative and sputum scarce patients in China. Simultaneous amplification and testing methods for detection of the Mycobacterium tuberculosis (MTB) complex (SAT-TB assay) is a novel molecular technique established in our hospital. This method has a high sensitivity and specificity in the lab. In this study, the clinical diagnostic performance of this method in smear-negative or sputum-scarce PTB suspects was investigated and evaluated.

Methods: Two hundred smear negative and 80 sputum-scarce patients were recruited in this study. Samples that included sputum or bronchial washing fluid were collected and sent for both bacteria culture and SAT-TB assay. Diagnosis for these patients was based on the comprehensive evaluation of chestX- ray/CT study, histology examination, lab results, and treatment response. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for each diagnostic test were investigated and calculated using confirmed tuberculosis (TB) and non-TB cases. The time required for detection of MTB was also measured for each method.

Results: Ninety-two patients (33%) were diagnosed as definitive TB, 112 patients (40%) were probable PTB, and 76 (27%) were non-TB. The sensitivity, specificity, PPV, and NPV of SAT-TB in smear-negative PTB suspects were 93% (95% CI, 84%-98%), 98% (95% CI, 90%-100%), 98% (95% CI, 91%-100%), and 93% (95% CI, 83%-98%). In sputum scarce PTB suspects, the sensitivity, specificity, PPV, and NPV of the SAT-TB assay on bronchial washing fluids were 90% (95% CI, 74%-98%), 100% (95% CI, 85%-100%), 100% (95% CI, 88%-100%), and 88% (95% CI, 69%-97%). The accuracy of the SAT-TB assay is consistent with the bacteria culture assay. The median time required for detecting MTB in the SAT-TB assay was 0.5 day, which was much faster than bacteria culture (28 days).

Conclusions: The SAT-TB assay is a fast and accurate method for the detection of MTB. It can be widely applied in the clinic and be an asset in early detection and management of PTB suspects, especially in those patients who are smear negative or sputum scarce.