Computational projection of virion transmission rates to the lower airway from the initial SARS-CoV-2 infection at the Nasopharynx

While the nasopharynx stands out as the dominant initial infection site for SARS-CoV-2, the physiological mechanism launching the lower airway infection is still not well-understood. Based on the speed of infection progress, it is thought that the nasopharynx acts as the seeding zone for subsequent contamination of the lower airway via aspiration of virus-laden boluses of nasopharyngeal fluids. We examine the plausibility of this transport process through computational fluid mechanics models of steady and forced breathing in five tomographic airway reconstructions, thereby quantifying the nasopharyngeal liquid volume transmitted to the lower airspace in each aspiration. Our model predicts 2-4 aspirations during an 8-hour sleep cycle, consistent with prior experimental data. Extending the numerical trends on aspiration volume to earlier records on aspiration frequency indicates a total aspirated nasopharyngeal liquid volume of 0.3±0.76 ml/day. Using sputum viral loads for hospitalized COVID-19 patients, we then estimate the number of virions transmitted daily to the lungs via nasopharyngeal liquid boluses. For peak sputum viral load, the number is 7.1 × 108±1.8 × 109 virions/day, well in excess of the estimated minimum infectious dose for SARS-CoV-2. These findings provide a mechanism for the progression of SARS-CoV-2 infection of the nasopharynx to the COVID-19 disease within a patient, and point to dysphagia as one of the potential underlying risk factors for adverse outcomes.

Aerosol generation during endonasal instrumentation in the clinic setting

Background: The potential risk for transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) duringendoscopic endonasal instrumentation has been described in recent anecdotal reports. Additionally, recent simulations incadaveric models have demonstrated aerosol generation during power endonasal instrumentation. Endonasal proceduresare commonly performed in the outpatient clinic setting, and with a potential for aerosol generation, these procedures maypose a potential exposure risk to clinic staff. Objective: To provide a greater understanding of aerosol generation and exposure risk during endoscopic endonasalinstrumentation in the outpatient clinic setting. Methods: Using an optical particle sizer, airborne particles concentrations in particles per cubic foot (p/ft ) were measuredduring 30 nasal endoscopies in the outpatient clinic setting. Aerosol measurements were collected within an 18-inch radiusfrom the patient's head during 11 different diagnostic nasal endoscopies and 19 different nasal endoscopies with suctionand mechanical debridement. To identify any particle effect from endonasal instrumentation, airborne particles measuring0.3, 0.5, 1.0, 2.5, 5.0, and 10.0 microns (μm) in diameter were recorded at distinct time points throughout diagnostic anddebridement endoscopies. To account for the effects of native patient breathing on aerosol concentrations, all endoscopymeasurements were compared to aerosol concentrations measured prior to procedure initiation. Results: Compared to preprocedure aerosol levels, no significant increase in mean aerosol concentrations was measuredduring diagnostic nasal endoscopies. However, compared to preprocedure aerosol levels, a statistically significant increasein mean particle concentrations was measured during cold instrumentation at 2,462 p/ft (95% CI: 837-4,088;p = 0.005).The use of suction instrumentation was also associated with a statistically significant increase in mean particleconcentrations at 2,973 p/ft (95% CI: 1,419-4,529;p = 0.001). In total, greater than 99% of all measured particles wereless than 2.5 μm in diameter, with comparable particle size distributions observed during all forms of endonasalinstrumentation. Conclusion: When measured with an optical particle sizer, diagnostic nasal endoscopy with a rigid endoscope is notassociated with increased particle aerosolization in patients for which sinonasal debridement is not indicated. In patientsneeding sinonasal debridement, the use of cold and suction instrumentation was associated with increased particle aerosolization. The observed generation of airborne particles, especially sub-micrometer aerosols, during endonasaldebridement may increase exposure risk for clinic staff to SARS-CoV-2 compared to patient native breathing. Appropriatepersonal protective equipment use and patient screening should be utilized for all office-based endonasal procedures.