SARS-CoV-2 in aerosol particles exhaled from COVID-19 infected patients during breathing, talking and singing

In the beginning of the COVID-19 pandemic, several super spreader events occurred during choir singing, which lead to an increased attention to airborne transmission of SARS-CoV-2. Since then, aerosol generation from singing has been studied in detail, however, mainly from healthy subjects. In this study, we collected aerosol particles in the exhaled breath of 38 COVID-19 infected patients during breathing, talking and singing, respectively, and analyzed the samples for detection of SARS-CoV-2.

Method
Patients that were contacted by the COVID-19 testing service due to a positive test result early in the phase of their infection (median 2, range: 0-6 days from symptom onset) were asked to volunteer for the study. A team of researchers drove a small truck hosting a mobile laboratory to the home address of the patient to perform exhaled breath aerosol collection using a condensational particle collector (BioSpot, Aerosol Devices) and a two-stage cyclone sampler (NIOSH bc-251, Tisch Environmental). Samples were collected for 10 min each when the patients were breathing, talking and singing, respectively. In addition, patient samples from nasopharynx and saliva were collected, and patients filled out a questionnaire about symptoms. All samples were stored at -80 °C until RNA extraction and analysis by reverse transcription quantitative polymerase chain reaction (RT-qPCR) targeting the N-gene.

Results
A first preliminary screening of air samples collected with the BioSpot showed that SARS-CoV-2 could be detected in the exhaled aerosols from 14 of 38 (37%) patients during respiratory activities. 50% of patients in the early phase of the infection, day 0-1 from symptom onset, emitted detectable levels of airborne SARS-CoV-2 RNA, 35% of patients on day 2-3, and 0% of patients on day 4-6. The highest viral RNA concentrations in aerosol samples were found in those collected during singing. Further analysis is ongoing and we hope that our results will contribute to quantifying and understanding the Covid-19 transmission via the airborne route.

This study was approved by the Swedish Ethics Review Authority (2020-07103). This work was supported by AFA Insurances and the Swedish Research Council FORMAS.