Rapid quantitative PCR on tongue swabs for pulmonary tuberculosis in adults: a prospective multicentre study

Tuberculosis (TB) remains a major cause of infectious disease mortality globally, with significant underdiagnosis perpetuating transmission. Tongue swab analysis has emerged as a promising non-invasive method for pulmonary TB diagnosis. This study evaluates the diagnostic accuracy of the TB-EASY quantitative PCR (qPCR) assay using tongue swab specimens.

In this prospective multicentre study, conducted across seven designated TB hospitals in China, 729 participants were included in the analysis. Tongue swabs were tested using the new TB-EASY assay from Hugobiotech, while sputum samples were analysed by Xpert MTB/RIF (Xpert), smear and culture tests. Diagnostic performance was compared to a composite microbiological reference standard (MRS).

The TB-EASY assay demonstrated high diagnostic accuracy, with sensitivity and specificity of 89.6% and 96.2% compared to sputum Xpert, and 87.4% and 98.0% compared to the MRS. Sensitivity varied by bacterial load, ranging from 100% in high-load cases to 70.4% in very-low-load cases. The assay demonstrated robust performance in diverse epidemiological settings.

The TB-EASY qPCR assay using tongue swabs offers a reliable, non-invasive diagnostic alternative for pulmonary TB, especially where sputum collection is challenging. Its potential for wider use in high TB burden settings warrants further validation in community-based studies. Limitations include potential overestimation of sensitivity due to the selection of symptomatic patients and the use of sputum Xpert rather than Xpert Ultra. Additionally, the performance in non-sputum-producing patients remains untested, and the cost-effectiveness should be further evaluated to assess the feasibility of its implementation.