key: cord-1018382-p8h2gdqb
authors: Hanrath, A. T.; Schim van der Loef, I.; Lendrem, D. W.; Baker, K. F.; Price, D. A.; McDowall, P.; McDowall, K.; Cook, S.; Towns, P.; Schwab, U.; Evans, A.; Dixon, J.; Collins, J.; Burton-Fanning, S.; Saunders, D.; Harwood, J.; Samuel, J.; Schmid, M. L.; Pareja-Cebrian, L.; Hunter, E.; Murphy, E.; Taha, Y.; Payne, B. A. I.; Duncan, C. J. A.
title: SARS-CoV-2 testing of 11,884 healthcare workers at an acute NHS hospital trust in England: a retrospective analysis
date: 2020-12-22
journal: nan
DOI: 10.1101/2020.12.22.20242362
sha: 175324f69ee3deb94ea27c56e9c0be91c708d31e
doc_id: 1018382
cord_uid: p8h2gdqb

Healthcare workers (HCWs) are known to be at increased risk of infection with SARS-CoV-2, although whether these risks are equal across all roles is uncertain. Here we report a retrospective analysis of a large real-world dataset obtained from 10 March to 6 July 2020 in an NHS Foundation Trust in England with 17,126 employees. 3,338 HCWs underwent symptomatic PCR testing (14.4% positive, 2.8% of all staff) and 11,103 HCWs underwent serological testing for SARS-CoV-2 IgG (8.4% positive, 5.5% of all staff). Seropositivity was lower than other hospital settings in England but higher than community estimates. Increased test positivity rates were observed in HCWs from BAME backgrounds and residents in areas of higher social deprivation. A logistic regression model adjusting for these factors showed significant increases in the odds of testing positive in certain occupational groups, most notably domestic services staff, nurses and health-care assistants. PCR testing of symptomatic HCWs appeared to underestimate overall infection levels, probably due to asymptomatic seroconversion. Clinical outcomes were reassuring, with only a small minority of HCWs with COVID-19 requiring hospitalisation (2.3%) or ICU management (0.7%) and with no deaths. Despite a relatively low level of HCW infection compared to other UK cohorts, there were nevertheless important differences in test positivity rates between occupational groups, robust to adjustment for demographic factors such as ethnic background and social deprivation. Quantitative and qualitative studies are needed to better understand the factors contributing to this risk. Robust informatics solutions for HCW exposure data are essential to inform occupational monitoring.

The pandemic of SARS-CoV-2 serves to highlight the risk posed to healthcare workers (HCWs) by 2 transmissible respiratory pathogens (1-7). As is the case for other highly pathogenic coronaviruses 3 8

and out of the logistic regression supplemented by generalized linear regression. While the Ab 3 9

positivity rates were higher for those presenting with a prior history of PCR testing, there was no 4 0 statistically significant interaction between Staff Roles and Phase (p=0.6963). The interaction term 4 1 was dropped, and the odds ratios and 95% confidence intervals constructed for the comparison of 4 2 each of the Staff Roles relative to the minimal exposure group (Administrative and Managerial).

All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 22, 2020. ; https://doi.org/10.1101 https://doi.org/10. /2020 RESULTS 1 2 PCR testing 3 From 10 March to 6 July 2020, NUTH laboratories processed and provided SARS-CoV-2 PCR results 4 on 44,781 combined nose/throat swabs. During this period, 3,721 PCR tests were undertaken on 3,338 5 HCWs who had contacted the symptomatic testing programme (representing 19.5% of all NUTH 6 employees). The median (IQR) turnaround time from samples arriving in the laboratory to a result 7 being available was 7.8 (6.5 -10.5) hours. In total 481/3,338 symptomatic HCWs tested positive for 8 SARS-CoV-2 by .6%] of those tested; 2.8% [2.6-3.1%] of all HCWs in 9 the organisation). The number of HCWs presenting for testing and the rate of positive tests fluctuated during the study 1 3

period, corresponding to the dynamics of SARS-CoV-2 transmission in the region (Figure 1) . The 1 4

number of tests performed per day ranged from three to 169 (Figure 2A ). Most positive PCR tests deprived three quartiles (χ²test p < 0.001). All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 22, 2020. ; https://doi.org/10.1101 https://doi.org/10. /2020 To explore associations between occupational role and the proportion of positive tests (defined as 1 individuals with a positive test by PCR and/or antibody as a percentage of all those tested), HCWs 2 were grouped into 12 categories based on roles recorded in ESR (as discussed in Appendix 1).

Logistic regression analysis was performed adjusting for the demographic factors described above 4 ( Table 1) . The administrative and managerial, non-patient facing group was used as the comparator 5 for this analysis based on the fact that their role does not require close contact with patients or the 6 hospital environment and that many of these staff work in an off-site location separate from the 7 hospital sites. odds ratios and 95% confidence intervals for antibody and PCR positivity for each of the roles relative 1 7

to administrative and managerial workers (the reference group) are shown in Figure 4A All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The data we report here span the first wave of the SARS-CoV-2 epidemic in England and represent 3 among the largest combined molecular and serological testing datasets in a HCW population. Nearly 4 one in five employees in this large organisation presented for PCR testing during the study period and 5 14.4% percent of those tested (2.8% of the workforce) had symptomatic SARS-CoV-2 infection 6 detected by PCR. Over two thirds of the total workforce (over 10,000 HCWs) underwent antibody 7 testing. 8.4% of those tested (5.5% of the workforce) were seropositive. This compares to 8 seroprevalence estimates of 6.0% for England and 5.0% for the North East of England around the 9 same period (21) and is consistent with increased exposure in HCWs. These positivity rates are considerably lower than rates among HCWs in some areas of England, such 1 2 as London (3), Birmingham (7), and in other parts of the North East (12), although are similar to other 1 3 regions such as Oxford (2) and Cambridge (14). Factors determining the regional variation in HCW despite the fact that most HCWs continued to commute to work and mix in the hospital environment. challenge of physical distancing in these and other healthcare settings (23). In our analysis, baseline factors associated with seroconversion included being from black, Asian and suggesting factors beyond patient contact may be involved. Other interesting observations also emerged from the analysis. Among non-clinical HCWs exposed to 3 7 the hospital environment, domestic services and estates/catering workers were more likely to test 3 8 positive, whereas laboratory workers handling potentially infectious specimens were not.

Administrative staff working in the hospital environment (such as receptionists and ward clerks) had domestic services workers as well as those HCWs from BAME backgrounds (2, 7). Whilst the 5 5

All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The symptom-based testing approach we employed appears to have underestimated total HCW between 4 and 41% of SARS-CoV-2 infections are asymptomatic (15). A large proportion of cases 5 0 may be missed by a symptom-based testing approach, consistent with our observations. Recent data in

HCWs have confirmed that asymptomatic SARS-CoV-2 infection does occur (2, 3, 7, 13, 14) and this 5 2 is central to the argument for asymptomatic screening (1). This is a reasonable approach in low 5 3 incidence settings. However important uncertainties to be balanced against asymptomatic HCW 5 4

screening are the extent to which asymptomatic HCWs transmit SARS-CoV-2 (15), alongside more 5 5

All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 22, 2020. ; https://doi.org/10.1101 https://doi.org/10. /2020 pragmatic considerations such as how frequently to screen and how to deal with the issue of 1 prolonged asymptomatic shedding of SARS-CoV-2 RNA, which occurs in between a quarter (2) and 1 0 1 1

In summary, the data reported here demonstrate that despite a relatively low level of infection 1 2 compared to other UK HCW cohorts, there was an important differential risk of infection between 1 3 occupational groups, robust to adjustment for other demographic factors such as BAME background 1 4

and social deprivation. This finding adds to the growing evidence of differential risks among HCWs.

In order to better understand the factors contributing to these risks, prospective quantitative and All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. All rights reserved. No reuse allowed without permission. preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this this version posted December 22, 2020. ; https://doi.org/10.1101 https://doi.org/10. /2020 

COVID-19: the case