Airborne Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Hospitals: Effects of Aerosol-Generating Procedures, HEPA-Filtration Units, Patient Viral Load, and Physical Distance

Abstract

Background Transmission of covid-19 can occur through inhalation of fine droplets or aerosols containing infectious virus. The objective of this study was to identify situations, patient characteristics, environmental parameters and aerosol-generating procedures (AGPs) associated with airborne SARS-CoV-2 virus. Methods Air samples were collected near hospitalised covid-19 patients and analysed by RT-qPCR. Results were related to distance to the patient, most recent patient diagnostic PCR Ct-value, room ventilation and ongoing potential AGP. Results In total 310 air samples were collected, and of these 26 (8%) were positive. Of the 231 samples from patient rooms, 22 (10%) were positive for SARS-CoV-2. Positive air samples were associated with a low patient Ct-value (OR 5.0 for a Ct-value <25 vs >25, p=0.01, 95% confidence interval 1.18 to 29.5) and a shorter physical distance to the patient (OR 2.0 for every meter closer to the patient, p=0.05, CI 1.0 to 3.8). A mobile HEPA-filtration unit in the room decreased the proportion of positive samples (OR 0.3, p=0.02, CI 0.12 to 0.98). No association was observed between SARS-CoV-2 positive air samples and mechanical ventilation, high flow nasal cannula, nebulizer treatment or non-invasive ventilation. An association was found with positive expiratory pressure (PEP) training (p<0.01) and a trend towards association for airway manipulation, including bronchoscopies and in- and extubations. Conclusions Our results show that major risk factors for airborne SARS-CoV-2 include short physical distance, high patient viral load and poor room ventilation. AGPs, as traditionally defined, seem to be of secondary importance.

Aerosol-Generating Procedures and Virus Transmission

“…51 Likewise, Thuresson et al found that the number of positive air samples with SARS-CoV-2 detection was similar in subjects treated with versus without respiratory support (HFNC or NIV). 52 Thus, we may conclude that neither NIV nor CPAP is an AGP. Vented masks should be avoided for patients with airborne disease; if tolerated, a helmet with an air cushion around the neck may be preferred.…”

A rapid review of Supplementary air filtration systems in health service settings. September 2022

“…▪ Two trials in the systematic review reported lower COVID-19 symptom scores with HEPA filtration (Daga et al 2021). ▪ Thuresson et al (2022) found that adding a mobile HEPA-filtration unit to rooms with regular ventilation was associated reduced SARS-CoV-2 RNA in the air. ▪ HEPA/UV filtration units greatly reduced particulate matter counts of all sizes (Sloof et al (2022).…”

“…▪ Two studies, (Conway Morris et al 2022, Daga et al 2021 were assessed as having high risk of bias concerns. ▪ Two observational studies (Sloof et al 2022, Thuresson et al 2022) and the modelling study (Buchan et al 2020) were assessed as having low risk of bias.…”

Revised Guidelines for Coronavirus Disease 19 Management in Hematopoietic Cell Transplantation and Cellular Therapy Recipients (August 2022)

“…Efforts to prevent transmission should focus on all key measures, with recommendations that take into consideration the level of community spread and the risk of transmission from mildly symptomatic or asymptomatic individuals. SARS CoV-2 is primarily transmitted through small and large respiratory droplets 101 , 102 , 103 . Long range transmission by small particle aerosols can happen and forms the basis of the current CDC guidance for transmission-based precautions.…”