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High levels of COVID-19 found in hospital air samples but few viable viruses

It is widely acknowledged that airborne transmission of COVID-19 can occur in crowded and closed environments. Given this potential for transmission, there is a real concern the virus might easily spread within a hospital leading to a serious outbreak.

Together with early evidence from China, available data has suggested that COVID-19 can be easily transmitted through the air. With an increasing number of patients being hospitalised because of COVID-19, a team from the UK and France wanted to examine all of the published evidence on air contamination surrounding patients and healthcare professionals in hospitals. They searched all the major databases from January 2020 to the end of October 2020, including preprint articles available on the servers BioRxiv and MedRxiv, as well as checking the reference list of identified articles. Information on the setting, ventilation system, number of air samplings performed, sampling methods and positivity rates were extracted. Furthermore, the data were classed in terms of the area examined e.g., close patient environments, toilets/bathrooms, clinical areas, staff areas and public areas including hallways and indoor or outdoor areas. The authors also looked for data on viral loads and viral culture results.

The authors initially found 2284 articles but after screening this reduced to only 24 and which were included in the analysis. All of the articles reported testing for COVID-19 using PCR and were cross-sectional observational studies. There were 893 air samples collected across the 24 studies including 52.7% (471) from close patient environments, 26.5% (237) from clinical areas (including 107 from intensive care units), 13.7% (122) from staff areas with the remainder collected from public areas and toilets and/or bathrooms. However, the positivity rates of samples were low with only 17.4% of those from patient areas testing positive. Within the clinical areas studied, the positivity rate varied between 25.2% in the 107 intensive care units and 10.7% from non-intensive care areas. In rooms with negative pressure, the positivity rate was 13.1% and the overall positivity rate for clinical areas was 8.4%. Interestingly, the positivity rate was 23.8% from toilets and or bathrooms. A recognised limitation of the study was the absence of testing for surface contamination.

Commenting on these findings, the authors noted that while many areas appeared to be contaminated with COVID-19, the actual levels of viable virus were actually very low.

Birgand G et al. Assessment of air contamination by SARS-CoV-2 in hospital settings. JAMA Netw Open 2020 doi:10.1001/jamanetworkopen.2020.33232

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