Assessment of Salivary Glands as Reservoirs of SARS-CoV-2 and the Contagiousness of Saliva in Asymptomatic COVID-19 Patients: Is Delta Variant More Contagious?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection transmits when aerosols or droplets containing the virus are inhaled or come directly into contact, mainly in close contact with an infected person.

This study aimed to evaluate the role of the salivary glands in the secretion of SARS-CoV-2-infected saliva and determine the contagiousness of saliva in asymptomatic coronavirus disease 2019 (COVID-19) patients.

In this cross-sectional analytical study between March 2021 and March 2022, 85 asymptomatic COVID-19 individuals with positive nasopharyngeal/oropharyngeal swabs were recruited. The SARS-CoV-2 cycle threshold (Ct) value was investigated in concomitant nasopharyngeal swabs (NPS), saliva, and pure saliva (collected directly from the salivary duct opening) using Real Time-PCR assay. Statistical analysis was performed using SPSS software (version 23), and a p-value of < 0.05 was considered significant.

The saliva Ct-value was the lowest (the highest viral load) for Delta (29.82 ± 4.66), Omicron (32.75 ± 4.82), and Alpha (36.83 ± 4.8) variants, respectively. Delta-infected saliva and pure saliva revealed the strongest correlation (correlation coefficient = 0.971, P< 0.001). Saliva Ct-value was significantly lower in Delta- (P < 0.001) and Omicron- (P = 0.012) infected patients than in Alpha-infected patients. The pure saliva Ct-value was significantly lower (P = 0.014) in Delta samples (30.13 ± 4.51). Asymptomatic Alpha- and Omicron-infected patients revealed significantly lower NPS Ct-value (30.52 ± 4.02 and 29.44 ± 3.34) than the saliva (36.83 ± 4.8 and 32.75 ± 4.82).

The major salivary glands secrete SARS-CoV-2-infected saliva in nearly all Delta-infected and most Omicron-infected asymptomatic individuals. Although the transmission process is complex, saliva droplets and aerosols seem to have a higher contagiousness potential in individuals infected with the Delta variant.