Detection of Mycobacterium tuberculosis complex in saliva by quantitative PCR: A potential alternative specimen for pulmonary tuberculosis diagnosis

Background Current tuberculosis (TB) diagnostic tests primarily rely on sputum samples, yet many TB patients cannot produce sputum. This study explored whether saliva could be used instead of sputum to diagnose pulmonary TB (PTB). Method The study included 32 patients with confirmed PTB and 30 patients with other respiratory diseases (ORD). Saliva from all study participants was subjected to quantitative (qPCR) assays targeting the IS1081 gene for detection of M. tuberculosis complex DNA. Results The sensitivity of saliva IS1081 qPCR was 65.6 % (95 % CI 48.4-80.2 %) with positive results for 21/32 PTB cases, while the specificity was 96.7 % (95 % CI 85.9-99.6 %) with negative results for 29/30 participants with ORD. Sensitivity improved to 72.4 % (95 % CI 54.6-86.0 %) when sputum-Xpert was used as the reference standard, while remaining similar at 65.5 % (95 % CI 47.4-80.7 %) when culture was used as the reference standard. In receiver operating characteristic (ROC) curve analysis, the area under the curve (AUC) for saliva IS1081 qPCR was 82.5 % (95 % CI 71.7-93.3 %). Conclusion Saliva testing offers a promising alternative to sputum for TB diagnosis among confirmed PTB cases. Larger multicenter studies, encompassing diverse clinical TB characteristics, are needed to provide improved estimates of diagnostic sensitivity and specificity.