Salivary exosomal Mycobacterium tuberculosis DNA enables sensitive detection of paucibacillary tuberculosis: a molecular diagnosis study.

BACKGROUND

Non-sputum-based tools are essential complements to the current tuberculosis diagnosis strategy. We aim to determine whether dual-gene qPCR melting curve detection of salivary exosomes Mycobacterium tuberculosis DNA can diagnose paucibacillary tuberculosis.

METHODS

We developed the exosomal nucleic acid (ExoNA)-based saliva tuberculosis diagnostic, a rapid, non-sputum diagnostic method for tuberculosis by integrating enrichment of salivary exosomes, nucleic acid extraction, and dual-target qPCR melting curve analysis. In a pilot clinical study, adults with suspected pulmonary tuberculosis were enrolled to evaluate diagnostic performance against multiple reference standards. Subgroup analysis was performed in patients with negative smear microscopy.

RESULTS

Salivary exosomal DNA was identified as the predominant form of detectable Mycobacterium tuberculosis DNA in saliva. ExoNA-based salivary tuberculosis diagnostic reduced the turnaround time from 16 h to 3h, and reached a limit of detection of 10 CFU/mL. In total, 130 patients with suspected pulmonary tuberculosis were included. Of them, 36·9% (48/130) were asymptomatic, and 80·8% (105/130) had negative smear microscopy results. The ExoNA-based Saliva TB assay had sensitivity of 81.2% (95% CI 53.7%-95.0%) and specificity of 82.8% (95% CI 63.5%-93.5%) against microbiological reference standards (n=45), while sensitivity of 68.4% (95% CI 54.6%-79.7%) and specificity of 82.9% (95% CI 67.4%-92.3%) under extended microbiological reference standards (n=98). In the subset of 105 patients with negative smear microscopy, the sensitivities remained within the range of 67.5% to 75.0% across different reference standards, and specificities ranged from 82.1% to 82.9%.

CONCLUSION

ExoNA-based saliva tuberculosis assay demonstrates favorable diagnostic performance in patients with suspected pulmonary tuberculosis, with the advantages of non-invasive nature, easy sampling, and rapid detection. Multicenter validation in more heterogeneous populations is necessary prior to clinical use.