Staff screening protocols
We previously described protocols for staff screening, sample collection, laboratory processing and results reporting in detail.1 These methods remained unchanged throughout this study period. Two parallel streams of entry into the testing programme included (i) HCW symptomatic, and HCW symptomatic household contact screening arms and (ii) an HCW asymptomatic screening arm . In the former, any patient-facing or non-patient-facing HCW could voluntarily refer themselves or a household contact, should they develop symptoms suggestive of COVID-19. In the latter, HCWs could volunteer to take part in a rolling programme of testing for all patient-facing and non-patient-facing staff working in defined clinical areas thought to be at risk of SARS-CoV-2 transmission. Testing was performed (i) at temporary on-site ‘Pods’; (ii) via self-swabbing kits delivered to HCWs in their area of work. All individuals in each arm of the programme performed a self-swab at the back of the throat then the nasal cavity, followed by RNA extraction and amplification using real-time RT-PCR.11 Cluster investigation was initiated when three or more HCWs working in the same clinical area tested positive for SARS-CoV-2 in a one week period.