SARS-CoV-2 transmission from the healthcare setting into the home: a prospective longitudinal cohort study
Authors: Craxford Simon , Nightingale Jessica , Ikram Adeel , Marson Ben Arthur , Kelly Anthony , Norrish Alan , Vijay Amrita , Astbury Stuart , Cusin Lola , Ashraf Waheed , Newham Jayne , Aithal Guruprasad , Tighe Patrick , Ball Jonathan , Tarr Alexander W , Urbanowicz Richard A , Valdes Ana , Ollivere Benjamin 
Published: February 2021

Objective
To assess the incidence of symptomatic and asymptomatic SARS-CoV-2 seropositivity in healthcare workers and subsequent transmission to their close contacts within their household. To assess changes in immunoglobulin (Ig) and neutralising antibodies (nAbs) in exposed participants.

Setting
Two acute National Health Service (NHS) hospitals within the East Midlands region of England.

Background
The UK has been one of the most severely affected countries during the COVID-19 pandemic. Transmission from healthcare workers to the wider community is a potential major vector for spread of SARS-CoV-2 which is not well described in the current literature.

Methods
Healthcare workers (HCW) were recruited from two Hospitals within the East Midlands of England and underwent serial blood sampling for anti-SARS-CoV-2 antibodies (both nucleocapsid and spike protein for IgG, IgM and IgA) between 20 April and 30 July 2020, with the presence of neutralising antibodies (nAbs) assessed for positive participants. Cohabitees of the volunteers were invited to attend testing in July -August 2020 and underwent identical serological testing as the HCWs.

Results
633 healthcare professionals were recruited. 178 household contacts of 137 professionals volunteered for the study. 18% of healthcare professionals (115 out of 633) tested as seropositive during the study period, compared to an estimated seroprevalence of 7% within the general population. The rate of symptomatic COVID-19 was 27.5% compared to an asymptomatic rate of 15.1%. Rates of positivity declined across the study period for all immunoglobulins (overall positivity from 16.7% to 6.9%).
7.2% of the cohabitees tested as seropositive. 58 cohabitees lived with a serologically positive HCW; this group had a seropositive rate of 15.5%, compared to 2.5% of cohabitees without a seropositive HCW, a six-fold increase in risk (Odds ratio 7.16 95% CI 1.86 to 27.59), p = 0.0025). Given the observed decay rates and data from Public Health England, we estimate that the proportion of seropositive cohabitees living with a seropositive HCW at the height of the first wave could have been as high as 44%.
110 out of 115 (95.7%) HCWs and 12 out of 13 (92.3%) cohabitees who tested positive developed detectable nAbs. 56.5% (65 out of 115) of SARS-CoV-2 positive HCWs developed a neutralising titre with an IC50 1/300 dilution; no cohabitee achieved this level.

Conclusions
Transmission of SARS-CoV-2 between healthcare professionals and their home contacts appears to be a significant factor of viral transmission, but, even accounting for the decline in seropositivity over time, less than 44% of adult cohabitees of seropositive healthcare workers became seropositive. Routine screening and priority vaccination of both healthcare professionals and their close contacts should be implemented to reduce viral transmission from hospitals to the community.