Utilization of Saliva for Anti-SARS-CoV-2 Antibody Detection in the General Population.

BACKGROUND: Similar to how salivary cortisol reflects serum cortisol as a stress biomarker, saliva by its easy, non-invasive collection, holds promise for mucosal antibody testing to assess systemic humoral immunity. In this study, we aimed to determine the prevalence of SARS-CoV-2 antibodies in saliva during the COVID-19 pandemic. METHODS: Between February and December 2022, paired saliva and serum specimens were collected twice per participant with the history of infection. SARS-CoV-2 antibodies were measured by Roche Elecsys anti-N and Abbott anti-S1-RBD assays. Cortisol was also quantified in serum-saliva paired samples using Elecsys Cortisol II. Saliva antibody results with manufacturer's serum cutoff were compared with those of the serum. RESULTS: Out of the 166 participants enrolled, the first and second visits showed serum anti-S1-RBD Ab in 162 (97.6%) and anti-N Ab in 79 (47.5%) and 97 (58.4%) participants. At the first and second visits, 14 (8.4%) and 13 (7.8%) participants had salivary anti-S1-RBD Ab, while 4 (2.4%) and 5 (3.0%) participants had anti-N Ab. Agreement between serum and saliva was slight for anti-S1-RBD (κ = 0.004) and poor for anti-N (κ < 0). The mean serum cortisol was 7.52 μg/dL (visit 1) and 7.97 μg/dL (visit 2) versus 0.19 μg/dL and 0.18 μg/dL in saliva. Saliva cortisol levels were ~ 95.5 - 97.6% lower than serum. CONCLUSIONS: Salivary SARS-CoV-2 antibody levels and serologic results are poorly concordant, preventing saliva as a direct substitute without assay-specific cutoffs. Salivary cortisol correlates predictably with serum levels but consistently underestimates them. Further work is needed to establish standardized saliva thresholds for both antibodies and cortisol.