Discussion
Our data demonstrate a dramatic fall in the prevalence of symptomatic
and asymptomatic SARS-CoV-2 infection amongst HCWs in our hospital
during the study period. On average, the number of secondary infections
amongst HCWs arising from each infected HCW (effectively, the
reproduction number (R) for SARS-CoV-2 transmission between HCWs) must
therefore be <1.
As well as acquisition from other HCWs, infections amongst HCWs may also
be acquired from patients, as well as other individuals outside the
hospital. Our study period coincided with a decline in the rate of
infection across our local community, and our data are consistent with a
reduction in transmission within the hospital, a reduction in
community-based acquisition of infection by HCWs, or (most likely) a
combination of both. In the absence of detailed epidemiological data, it
is not possible to formally differentiate between these possibilities or
determine their relative effect sizes. Nonetheless, our identification
of HCW infection clusters in specific areas of the hospital highlighted
the potential for workplace acquisition of SARS-CoV-2, which may lead to
self-sustaining outbreaks if left uninterrupted.1,8For each of these clusters, timely identification of HCW infection
proved effective in terminating chains of hospital transmission between
staff, preventing ongoing nosocomial infection.
With the incidence of infection having fallen significantly in
hospitalised patients, HCWs and the wider community, many hospitals
across the UK and further afield have been afforded precious time to
build the infrastructure necessary to establish comprehensive screening
programmes in anticipation of a possible second epidemic peak. For
hospitals already operating newly established screening programmes, the
challenge now is to up-scale to the point that screening can occur at a
frequency that permits pre-symptomatic capture of as close to 100% of
all new infections as possible. This approach will enable staff to be
removed from the workplace at the time of peak
infectivity.9 The minimum screening frequency required
needs to be carefully modelled, with recent estimates suggesting the
need for weekly testing to prevent 16-33% of onward transmission from
HCWs, depending on the time taken for results to be reported, and
another study estimating the need for daily screening to prevent 65% of
HCW-to-HCW transmission events.2,10 In practice, we
have observed good results in our hospital with a current frequency of
asymptomatic screening every 2-4 weeks. Those being screened are
prioritised by anticipated ward-based exposure to COVID-19, with
additional targeted screens triggered by excess staff sickness or the
identification of symptomatic cases on specific
wards.1 In addition to asymptomatic screening, testing
of symptomatic HCWs is essential for preventing excessive erosion of the
hospital workforce by self-isolation on the basis of symptoms alone, and
testing of symptomatic HCW household contacts negates the need for
unnecessary self-quarantine periods for co-habiting HCWs. We found
uptake to the HCW symptomatic household contact screening arm of our
programme to be notably lower than the HCW symptomatic arm despite
regular communications to advertise the service within CUHNFT. This lack
of uptake may reflect a lack of awareness that symptomatic non-HCWs were
eligible for testing, provided they shared a household with a hospital
employee. Many non-hospital employees may also have been more inclined
to attend national testing centres or be less aware of the spectrum of
COVID-19 symptoms.
Importantly, our data demonstrate that CUHNFT was not acting as an
independent ‘hub’ for ongoing COVID-19 transmission among HCWs. The
absence of nosocomial transmission likely reflects the combined efficacy
of HCW testing, stringent prospective and reactive infection prevention
and control measures, and appropriate social distancing amongst the
workforce. These findings should give reassurance to both hospital staff
and patients that healthcare facilities remain safe places to give and
receive care. Furthermore, since CUHNFT, with approximately 11,000 staff
members (many of whom are based in the hospital) is a major regional
employer, we predict that comparable organisations in other sectors may
also be able to resume on-site work safely by instigating similar
precautions.