SARS-CoV-2 spillover into hospital outdoor environments

SARS-CoV-2 spillover into hospital outdoor environments. Jefferson T, Spencer EA Hemeghan C.

Published on August 20, 2020

Reference Brown CS, Clare K, Chand M, et al. Snapshot PCR surveillance for SARS-CoV-2 in hospital staff in England. J Infect. 2020;81(3):427-434. 2020
Study type
Country UK
Setting Hospital (healthcare workers)
Funding Details PHE
Transmission mode Asymptomatic transmission, viral load

Bottom Line

In six UK hospitals in April-May 2020 the point prevalence of SARS-CoV-2 carriage was 2.0% (23/1152 participants) and the median cycle threshold value 35.7 (IQR:32.4–37.6).

When prevalence of COVID-19 is very low, routine and repeated screening is unlikely to have significant value. This is underlined by the finding that the majority of healthcare workers testing positive by PCR in this study were unlikely to be infectious.

Evidence Summary

23 of 1,152 participants tested positive (2.0%). This is higher than the estimate for the general population at the time.

Among these 23 positive test samples, median cycle threshold value was 35.7 (IQR:32.4–37.6). 

17 individuals were previously symptomatic, two currently symptomatic (isolated anosmia and sore throat); the remainder declared no prior or current symptoms. 

Symptoms in the past month were associated with threefold increased odds of testing positive (aOR 3.46, 95%CI 1.38–8.67; p = 0.008). 

SARS-CoV-2 virus was isolated from only one (5%) of nineteen cultured samples. It had a Ct value of 26. For that sample, no data on symptoms were available.

A large proportion (39%) of all 1.152 participants reported symptoms in the past month.

What did they do?

The study is a cross sectional survey carried in 1152 health care workers in six UK hospitals between 24 April and 7 May 2020 responding to a questionnaire. 93% of respondents worked in a patient-facing environment, 20% worked directly on COVID-19 wards and 38% reported that their work involved performing aerosol generating procedures (AGPs). 


The most frequent types of staff were nurses (30%), doctors (20%), occupational therapists and physiotherapists (7%), other allied clinical staff(6%) and cleaners (6%). 70% were females.

Participants volunteered to self-complete an anonymised health questionnaire and underwent a combined nose and throat swab. 

Samples were tested for SARS-CoV-2 using PCR. Viral culture was attempted on the majority of positive samples.  438 (39%) of respondents about symptoms (1125), had experienced at least one respiratory, gastrointestinal or influenza-like symptom in the previous month and 25% still had symptoms when they were tested.

A combined viral throat and nose swab was taken from each participant and placed in a viral and sent on the same day for detection of SARS-CoV-2 RNA by RT-PCR to the PHE national reference laboratory (five hospitals) or one hospital laboratory. The PHE laboratory used an Applied Biosystems 7500 FAST system targeting a conserved region of the SARS-CoV-2 open reading frame (ORF1ab) gene. 

The hospital laboratory used a different CE-IVD kit, targeting 3 SARS-CoV-2 genes (RdRp, E, and N). Both PCRs had internal controls. Viral culture of PHE laboratory positives was attempted in Vero E6 cells with virus detection confirmed by cytopathic effect up to 14 days post- inoculation.

Study reliability

This was a cross sectional survey in a convenience sample of hospitals . It is unclear how individuals were selected for participation and there may be bias in participation (those having experienced symptoms may be more motivated to take part). The only isolate could not be matched to a responding questionnaire.

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Unclear Unclear N/A N/A Unclear

What else should I consider?

This study reports similar results to other studies carried out in low prevalence situations. However, generalisation from a self selected subset of healthcare workers with missing information is not possible.


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.

Tom Jefferson

Tom Jefferson, epidemiologist.