Results
The total number of cases of SARS-CoV-2 infection amongst HCWs at CUHNFT increased throughout the study period, in keeping with the rising incidence of SARS-CoV-2 in the community (Figure 1 and Figure 1–source data 1 ). Similar proportions of cases were ascertained by symptomatic testing and asymptomatic screening on both green and red wards (Figure 1–figure supplement 1 ).
Prior to the change in RPE, cases per ward day were higher on red compared with green wards in seven out of eight weeks analysed (p=0.016, Wilcoxon signed-rank test, Figure 2 and Table 1 ). Following the change in RPE, the incidence of infection on red and green wards was similar, and not statistically different (p=0.5, Wilcoxon signed-rank test, Figure 2 and Table 1 ). Strikingly, there was a strong positive correlation between the incidence of SARS-CoV-2 in the community and the number of cases per ward day on green (R2=0.88) but not red wards (R2 = 0.01) (Figure 2–figure supplement 1 ). Taken together, these results suggest that the majority of cases among HCWs on green wards were caused by community-acquired infection, whereas cases among HCWs on red wards were caused by both community-acquired infection and direct, ward-based infection from patients with COVID-19, effectively mitigated by the use of FFP3 respirators.