Tongue swab Mycobacterium tuberculosis qPCR for community screening of asymptomatic TB vs. clinic-based triage of symptomatic TB.

BACKGROUND

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

METHODS

Tongue swabs were collected from adult household contacts of TB patients (HHC Cohort), and symptomatic adults presenting to clinics with presumptive TB (Clinic Cohort), at eight South African sites. TB Cases were defined by positive sputum Xpert Ultra or liquid culture, performed in all participants; and matched ~1:3 (HHC Cohort) or ~1:2 (Clinic Cohort) to Controls without TB. Tongue swabs in both cohorts were tested by high-volume qPCR; and in the Clinic Cohort, also by sequence-specific magnetic capture (SSMaC) with qPCR.

RESULTS

The Clinic Cohort included 217 TB Cases (100% symptomatic) and 437 Controls. The HHC Cohort included 44 TB Cases (84.1% asymptomatic) and 136 Controls. 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 = 0.14) (specificity 94.4%). Sensitivity of high-volume qPCR in the Clinic Cohort (63.8%) was significantly higher than the HHC Cohort (34.1%; p = 0.0007) (specificity 91.9%). Among HHC, high-volume qPCR sensitivity was 35.1% for asymptomatic TB; 52.2% for TB with abnormal CXR; and 100% for TB with High sputum Xpert Ultra grade.

CONCLUSIONS

Sensitivity of tongue swab high-volume qPCR for 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.