75Significant differences exist in the availability of healthcare worker (HCW) SARS-CoV-2 testing between 76 countries, and existing programmes focus on screening symptomatic rather than asymptomatic staff. Over a 77 3-week period (April 2020), 1,032 asymptomatic HCWs were screened for SARS-CoV-2 in a large UK 78 teaching hospital. Symptomatic staff and symptomatic household contacts were additionally tested. Real-79 time RT-PCR was used to detect viral RNA from a throat+nose self-swab. 3% of HCWs in the 80 asymptomatic screening group tested positive for SARS-CoV-2. 17/30 (57%) were truly 81 asymptomatic/pauci-symptomatic. 12/30 (40%) had experienced symptoms compatible with coronavirus 82 disease 2019 (COVID-19) >7 days prior to testing, most self-isolating, returning well. Clusters of HCW 83 infection were discovered on two independent wards. Viral genome sequencing showed that the majority of 84HCWs had the dominant lineage B•1. Our data demonstrates the utility of comprehensive screening of 85HCWs with minimal or no symptoms. This approach will be critical for protecting patients and hospital 86 staff. 87 88

Significant differences exist in the availability of healthcare worker (HCW) SARS-CoV-2 testing between countries, and existing programmes focus on screening symptomatic rather than asymptomatic staff. Over a 3-week period (April 2020), 1,032 asymptomatic HCWs were screened for SARS-CoV-2 in a large UK teaching hospital.Symptomatic staff and symptomatic household contacts were additionally tested. Realtime RT-PCR was used to detect viral RNA from a throat+nose self-swab.3% of HCWs in the asymptomatic screening group tested positive for SARS-CoV-2. 17/30 (57%) were truly asymptomatic/pauci-symptomatic. 12/30 (40%) had experienced symptoms compatible with coronavirus disease 2019 (COVID-19) >7 days prior to testing, most self-isolating, returning well. Clusters of HCW infection were discovered on two independent wards. Viral genome sequencing showed that the majority of HCWs had the dominant lineage B•1. Our data demonstrates the utility of comprehensive screening of HCWs with minimal or no symptoms. This approach will be critical for protecting patients and hospital staff.

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