Detection of SARS-CoV-2 Virions and RNA in Aerosols From COVID-19 Environments

Abstract

Background: Characterizing aerosols produced by SARS-CoV-2 patients is crucial for understanding disease transmission. The appearance and dispersal patterns of SARS-CoV-2 viral particles in airborne samples are not yet well understood. Knowing what SARS-CoV-2 particles look like just before they pass from one person to another can provide valuable insights into the mechanism of viral transmission through the air.

Methods: Samples from the upper respiratory tract and environmental aerosols were collected from 39 SARS-CoV-2–positive patients at different stages of symptom onset and from two distances from the source: 1 and 2 m. In addition, two nasopharyngeal samples from non-COVID-19 patients and aerosol samples from empty rooms and rooms of healthy individuals were taken as controls. Samples were analyzed by RT-PCR to detect viral RNA and by field emission scanning electron microscopy (FESEM) to visualize viral particles. Part of the nasopharyngeal and aerosol samples was studied by immunoelectron microscopy using nanogold particles against the spike protein to confirm the specific of the method.

Results: SARS-CoV-2 RNA was detected in 59.18% of aerosols from the environments of COVID-19 patients, with no significant differences based on distance. Higher detection rates were noted when the patient’s viral load was Ct ≤ 25. Intact viral particles were observed in nasopharyngeal samples from asymptomatic patients or those early progression of disease, either as free or clumped particles with well-defined spikes. In contrast, symptomatic patients had particles in mucus without visible spikes. Virus-like particles were visualized in aerosol samples at both distances.

Conclusion: Virions from asymptomatic patients or those in the early stages of the disease exhibited a better-conserved appearance in nasopharyngeal samples. Although RNA and virions of SARS-CoV-2 were detected in aerosol samples collected up to 2 m away from patients, only virion components, rather than complete virions, were observed. To our knowledge, this is the first report showing the appearance of three-dimensional SARS-CoV-2 particles in nasopharyngeal and air samples.