Mycobacterium tuberculosis DNA detection on tongue swabs: Effect of anti-tuberculosis drug treatment

Oral swab analysis (OSA) can be used to detect Mycobacterium tuberculosis (MTB) DNA in patients with pulmonary tuberculosis (TB). No previous analyses have investigated the effect of anti-tuberculosis drug treatment on MTB detection via oral swabs. This study, using a cross-sectional design, evaluated the sensitivity and specificity of OSA post-treatment initiation relative to sputum culture. Oral swabs were collected from adults with pulmonary TB (age 18-50; N = 26-33) at months 0, 2, 4, and 6 post initiation of treatment at a clinical site in South Africa. Sputa were also collected and tested by Cepheid GeneXpert MTB/RIF Ultra (Xpert Ultra) and mycobacteriological culture. Treatment was effective in all patients as determined by sputum culture and clinical outcomes. MTB DNA was extracted from swabs and concentrated by ethanol precipitation. MTB DNA in the samples was detected by using a qPCR assay that is specific to the M. tuberculosis complex IS6110 insertion element. OSA had a sensitivity of 74% and a specificity of 100% at month 0, with lower sensitivity and specificity at months 2 (sensitivity: 33%, specificity: 77%), 4 (sensitivity: NA, specificity: 89%), and 6 (sensitivity: NA, specificity: 76%). The reduced specificity at later months shows that OSA is susceptible to false-positive MTB DNA detection post-treatment, like sputum-based nucleic-acid amplification tests. These findings show that while OSA is promising for diagnosing TB, caution should be used when applying the method to patients post-treatment.