(A-B ) Comparison of modelled and actual cases. The model (black
dashed line) aimed to reproduce the risks of infection among HCWs per
ward day (A) on green wards (green solid line) and (B)on red wards (red solid line). (C) Risks inferred from the
model. HCWs were vulnerable to COVID-19 infection from exposure to
individuals in the community, with this risk increasing with community
incidence (grey line). HCWs working on green wards faced a consistent,
low risk of infection from direct, ward-based exposure (green line).
HCWs working on red wards initially faced a much higher risk of
infection from direct, ward-based exposure, falling to zero (confidence
interval [0, 0.0804]) upon the introduction of FFP3 respirators. In
this figure risks are expressed per ward day; a risk of 0.1 indicates
that a particular source of risk would be expected to cause one HCW from
the multiple staff present on a ward to develop an infection every 10
days that the ward was in operation. (D-E) Proportion of
community-acquired cases. Proportion of infections on (D ) green
and (E ) red wards inferred to have arisen via exposure to
individuals in the community (green line, green wards; red line, red
wards; confidence intervals shaded).