In silico determination of the temporal viral loads in the saliva and exhaled droplets from the oral cavity

Background and objective

The public health crisis triggered by the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) highlights the importance of the in-depth understanding of viral replication and re-emission mechanisms during coughing.

Methods

In this study, we used a Host-cell dynamics (HCD) model to characterize the replication kinetics of SARS-CoV-2 in the saliva of the oral cavity and optimized the fitting parameters based on clinical data to improve the viral load prediction accuracy. The Eulerian wall film model was integrated with the HCD model to quantify the viral load in the exhaled droplets during coughing. Additionally, variations in the oral cavity geometry were considered to determine its impact on the transmission risk of virus-laden droplets.

Results

HCD model showed that viral load in the oral cavity rose rapidly and peaked at around 10⁷ copies/mL during the incubation period (days −5 to −1), suggesting it as a major site for early viral replication. Integrated analysis revealed that the viral load of exhaled droplets was highly correlated with that of saliva, implying that a high viral load in the oral region exacerbates the transmission risk in the asymptomatic phase. Moreover, differences in oral cavity structure led to variations in the viral load carried by escaped droplets, thereby affecting the quantitative assessment of transmissibility.

Conclusions

This study systematically analyzed the dynamics of SARS-CoV-2 infection in the oral cavity. Our HCD-Eulerian wall film coupling approach provides a quantitative analytical tool to comprehensively assess all processes, from initial infection to inter-individual transmission, revealing the critical roles of the oral cavity in viral replication and droplet escape. These findings offer scientific insights for individual protection, airborne transmission risk assessment, and optimization of public health strategies.