Tongue Swab Mycobacterium tuberculosis Quantitative Polymerase Chain Reaction for Community Screening of Asymptomatic Tuberculosis Versus Clinic-Based Triage of Symptomatic Tuberculosis.

BACKGROUND

Diagnostic performance of tongue swab Mycobacterium tuberculosis polymerase chain reaction (PCR) has been evaluated for triage of symptomatic tuberculosis (TB). It is unknown whether performance differs for detection of asymptomatic TB in community-based screening.

METHODS

Tongue swabs were collected from adult household contacts of persons with TB (HHC cohort), and symptomatic adults presenting with presumptive TB (clinic cohort), at six South African sites. Drug-susceptible pulmonary TB was defined by positive sputum Xpert Ultra (excluding trace) or liquid culture, which were performed in all participants. Tongue swabs from participants with and without TB, matched by propensity score, were tested by high-volume quantitative PCR (qPCR) and, in the clinic cohort, also by sequence-specific magnetic capture (SSMaC) with qPCR.

RESULTS

The clinic cohort included 217 participants with TB (100% symptomatic) and 437 participants without TB. The HHC cohort included 44 participants with TB (84.1% asymptomatic) and 136 participants without TB. In the clinic cohort, sensitivity of SSMaC with qPCR was 73.2% (specificity 94.6%), but not significantly higher than high-volume qPCR (63.8%; P = .14) (specificity 94.4%). Sensitivity of high-volume qPCR in the clinic cohort (63.8%) was significantly higher than the HHC cohort (34.1%; P = .0007) (specificity 91.9%). Among HHC, high-volume qPCR sensitivity was 35.1% for asymptomatic TB, 52.2% for TB with abnormal chest radiograph, and 100% for TB with high sputum Xpert Ultra grade.

CONCLUSIONS

Sensitivity of tongue swab high-volume qPCR in community-based, household screening for asymptomatic TB was low, approximately half that of facility-based triage for symptomatic TB, but increased with radiographic severity and sputum bacillary load.