Application of oral fluid for quantitative nucleic acid and antibody detection of the severe acute respiratory syndrome coronavirus 2.

Introduction: To evaluate the performance of oral fluid (OF) for quantitative detection of SARS-CoV-2 nucleic acid and IgG antibody, and explore its application value, we compared OF with traditional samples using multiple detection methods. Methods: Real-time PCR (RT-PCR) and digital PCR (dPCR) were used to detect SARS-CoV-2 nucleic acid in 213 paired OF and throat swab samples from COVID-19 cases. Chemiluminescence was applied to detect IgG antibody in paired OF and serum samples, while colloidal gold method was used specifically for OF. Results: RT-PCR results showed that the positivity rates of OF and throat swabs were 80.75% (172/213) and 88.73% (189/213) respectively (p < 0.001). Using throat swabs as the reference, the sensitivity of OF for nucleic acid detection by RT-PCR was 87.83% (172/189). For 108 paired samples analyzed by dPCR, the positivity rate of OF was 86.11% (93/108), slightly higher than that by RT-PCR (85.19%, 92/108). Notably, in some cases, the viral load in OF exceeded that in throat swabs, accounting for 38.89% (N gene) to 41.67% (ORF1ab gene) of the tested samples. Conclusion: As a non-invasive, convenient, safe, and self-collectible biological sample, OF shows high consistency in detection efficacy compared with traditional throat swabs and serum. It thus holds important application value for the diagnosis, monitoring, and epidemic prevention and control of COVID-19.