A study presenting evidence for the presence of SARS-CoV-2 RNA in the air has been published. Environmental monitoring of two hospitals and some public areas in Wuhan, China, reveals hotspots for airborne viral RNA, but whether this material has the potential to infect was not assessed. Although the sample sizes are small (fewer than 40 samples from 31 locations), the findings by researchers at the Hong Kong University of Science and Technology, Wuhan University, Fudan University, Shanghai, and the Shanghai Environmental Monitoring Centre, support notions that careful sanitisation, good ventilation and avoidance of crowds can reduce the risk of airborne virus exposure.
Reported modes of SARS-CoV-2 RNA transmission to humans include close contact with infected individuals, contact with contaminated surfaces or inhalation of droplets released from the respiratory system of people with the virus. Whether there is further potential for SARS-CoV-2 to spread through the air has been less clear.
Ke Lan and colleagues set up aerosol traps in and around two government-designated hospitals for the treatment of patients with COVID-19 (the disease caused by SARS-CoV-2 infection) during February and March 2020. These sites included a grade-A tertiary hospital for patients with severe illness and a field hospital (a converted stadium) for patients with mild symptoms.
The concentration in ventilated patient wards was generally very low, which the authors attribute to effective isolation and high air exchange. Patient toilets, which were not ventilated, had elevated concentrations of airborne viral RNA. The authors found that RNA was especially concentrated in areas used by medical staff to take off protective equipment, which suggests that virus-laden aerosols can become resuspended in the air when this equipment is removed. However, after increasing the rigour and frequency of sanitization efforts, no detectable evidence of airborne SARS-CoV-2 RNA was found in medical staff areas.
Concentrations of SARS-CoV-2 RNA in public areas outside the hospitals such as residential buildings and supermarkets, were generally low. However, two areas that were subject to large crowds passing through, including an outdoor space near to one of the hospitals, had elevated concentrations of SARS-CoV-2 RNA. The authors suggest that individuals infected with SARS-CoV-2 within these crowded areas may have contributed to the viral aerosols.
This study does not investigate whether the SARS-CoV-2 RNA has the potential to be infectious, and restricted access to the hospitals during the peak outbreak limited the number of samples that could be taken. Nonetheless, the study supports the use of thorough sterilisation of the potential hotspots for virus-laden aerosols, well-ventilated hospitals and avoidance of crowds to reduce the risk of infection.
Abstract
While the transmission of SARS-CoV-2 via human respiratory droplets and direct contact is clear, the potential for aerosol transmission is poorly understood1–3. This study investigated the aerodynamic nature of SARS-CoV-2 by measuring viral RNA in aerosols in different areas of two Wuhan hospitals during the COVID-19 outbreak in February and March 2020. The concentration of SARS-CoV-2 RNA in aerosols detected in isolation wards and ventilated patient rooms was very low, but it was elevated in the patients’ toilet areas. Levels of airborne SARS-CoV-2 RNA in the majority of public areas was undetectable except in two areas prone to crowding, possibly due to infected carriers in the crowd. We found that some medical staff areas initially had high concentrations of viral RNA with aerosol size distributions showing peaks in submicrometre and/or supermicrometre regions, but these levels were reduced to undetectable levels after implementation of rigorous sanitization procedures. Although we have not established the infectivity of the virus detected in these hospital areas, we propose that SARS-CoV-2 may have the potential to be transmitted via aerosols. Our results indicate that room ventilation, open space, sanitization of protective apparel, and proper use and disinfection of toilet areas can effectively limit the concentration of SARS-CoV-2 RNA in aerosols. Future work should explore the infectivity of aerosolized virus.
Authors
Yuan Liu, Zhi Ning, Yu Chen, Ming Guo, Yingle Liu, Nirmal Kumar Gali, Li Sun, Yusen Duan, Jing Cai, Dane Westerdahl, Xinjin Liu, Ke Xu, Kin-fai Ho, Haidong Kan, Qingyan Fu, Ke Lan
[link url="https://www.nature.com/articles/s41586-020-2271-3"]Nature abstract (unedited)[/link]