Investigating SARS-CoV-2 surface and air contamination in a London hospital

COVID-19: Investigating SARS-CoV-2 surface and air contamination in a London hospital. Spencer EA, Heneghan C.

Published on July 1, 2020

Reference Zhou J, Otter J, Price JR, C et al. Investigating SARS-CoV-2 surface and air contamination in an acute healthcare setting during the peak of the COVID-19 pandemic in London. medRxiv 2020.05.24.20110346;  2020
Study type
Country UK
Setting Hospital
Funding Details Support form the NIHR Imperial Biomedical Research Centre, the Health Research Health Protection Research Unit in Respiratory Infections at Imperial College.
Transmission mode Aerosol, Fomite
Exposures Surface and air contamination

Bottom Line

Many hospital surfaces and air samples contained viral RNA. Viable virus was not cultured from any sample.

Evidence Summary

Viral RNA was detected on 114/218 (52%) of surfaces and 14/31 (30%) air samples. The proportion of surface samples contaminated with viral RNA varied by item sampled and by the clinical area. Viable virus was not cultured from any of the air or surface samples.

Viral RNA was detected on surfaces and in the air in public areas of the hospital and was more likely to be found in areas immediately occupied by COVID-19 patients than in other areas 64% vs 45%, p=0.025).  The high PCR Ct value* for all samples (>30) indicated that the virus would not be culturable.

*PCR vt value is the number of amplification cycles required to reach a fixed signal threshold

What did they do?

Cross-sectional observational study in a multi-site London hospital. 

Air and surface samples were collected from seven clinical areas, occupied by patients with COVID-19, and a public area of the hospital. Three or four 1.0 m3 air samples were collected in each area using an active air sampler. Surface samples were collected by swabbing items in the immediate vicinity of each air sample. SARS-CoV-2 was detected by RT-qPCR and viral culture; the limit of detection for culturing SARS-CoV-2 from surfaces was determined.

Study reliability

The inability to culture virus from the samples may be explained by the low RNA levels or the length of time since deposition or both. It is also possible that virus elements found were infectious but not culturable in the laboratory.

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes No Yes No Unclear

What else should I consider?

It is difficult to compare results with other similar studies due to varied sampling strategies.  This study does not have information on how the results relate to patient virus levels. 

About the authors

Carl Heneghan

Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings

Elizabeth Spencer

Dr Elizabeth Spencer; MMedSci, PhD. Epidemiologist, Nuffield Department for Primary Care Health Sciences, University of Oxford.