CoTB: Non-invasive tongue swabbing for duplex diagnosis of tuberculosis and COVID-19
Background and rationale: Non-invasive, high-throughput screening is essential for control of respiratory diseases including tuberculosis (TB) and COVID-19. Sample acquisition remains a critical bottleneck. Sputum and nasopharyngeal (NP) swab collection (for TB and COVID-19, respectively) are logistically challenging in the clinic, hazardous to healthcare workers (HCW), and nearly impossible in community settings. In contrast, self-collected oral or nasal swabs are faster, better tolerated, and safer for HCW.
Although biologically dissimilar, Mycobacterium tuberculosis and SARS-CoV-2 share important features as respiratory pathogens. Both are airborne diseases whose clinical presentations include fever, cough, fatigue, difficulty breathing, and chills. It is critical to test for both in clinical and community settings where either disease is a threat. Unfortunately, nearly all national programs report competition for resources needed to fight TB. Duplex sampling for both pathogens, such that every COVID-19 sample can be tested for TB and vice-versa, would be help to mitigate this problem.
Approach: We evaluated self-collected tongue, nasal (anterior nares), and mid-turbinate (MT) swabs as samples for SARS-CoV-2 diagnosis by RT-PCR. Diagnostic yields of these methods were quantified relative to standard NP swabbing. Since tongue swabbing was previously shown to also detect active TB, swabbing protocols were improved to increase sample yield from the tongue dorsum.
Results: Sensitivities of patient-collected tongue, nasal, and MP swabs relative to clinician-collected NP swabs were 89.8% (95% CI: 80.2 -100.0), 94.0 (95% CI: 84.6-100.0) and 96.2 (95% CI: 87.7-100.0), respectively. Based on these results the US FDA updated its guidance to recommend nasal swabbing as an alternative to NP. In a step toward duplex sampling for TB and COVID-19, tongue swabbing protocols were further optimized by using a bacterial biomass proxy. Foam swabs and “double swabbing” with flocked swabs were found to at least quadruple sample mass collection, relative to previously reported methods that used single flocked swabs. An enhanced sample collection protocol exhibited 93% sensitivity and 66% specificity relative to sputum culture in a TB cohort in Kampala, Uganda.
Conclusions: Tongue swabs are easy to collect from any adult or child, in any setting, and show promise as non-invasive samples for diagnosis of both TB and COVID-19. With further development this approach could potentially facilitate duplex diagnosis of both diseases.