Table 1. Combined data for SARS-CoV-2 RNA positive HCWs by role and
screening arm, from the present study and our previous
study1. Difference in proportions of HCWs testing
positive through the symptomatic screening arm was analysed using
Pearson’s chi-square test.
Overall, 360 individuals underwent repeat testing, either as part of the
asymptomatic screening programme, or for other reasons as previously
described.1 Median turnaround time from sample arrival
in the laboratory to final verification was 18 hours 45 mins. Positive
results were called out on the same day, with negative results emailed
within 24 hours.
Between 25th April 2020 and 24th May
2020, a total of 34 new positive tests were reported. In the HCW
symptomatic and HCW symptomatic household contact screening armscombined (reflecting all individuals with self-reported symptoms at the
time of testing), 13/771 (1.7%) tests were positive, which was
significantly lower than 30/221(13%) in the original study period
(Fisher’s exact test p<0.0001). In the HCW asymptomatic
screening arm, 21/2,611 (0.8%) tests were positive, which again was
significantly lower than 31/1,032 (3%) in the original study period
(Fisher’s exact test p<0.0001). As we previously
observed1, individuals captured in the HCW
asymptomatic screening arm were generally asymptomatic at the time of
screening, however these individuals could be divided into sub-groups.
In the first subgroup, 8/21 (38%) HCWs had no symptoms at all. Of
these, 5/8 (63%) remained entirely asymptomatic 5-7 weeks after their
positive test, whereas 2/8 (25%) developed symptoms 24 – 48 h after
testing. One HCW could not be contacted to obtain further history. In
the second subgroup, 6/21 (29%) had retrospectively experienced some
symptoms prior to screening. Of these, 5/6 (83%) had symptoms with a
high pre-test probability of COVID-191 commencing
>7 days prior to screening, of whom 3/5 had appropriately
self-isolated then returned to work, and 1/5 was tested shortly after
developing symptoms. 1/6 (17%) had symptoms with a low pre-test
probability of COVID-191 commencing <7 days
prior to screening and had not self-isolated. In the third subgroup,
7/21 (33%) were detected through repeat sampling of HCW who previously
tested positive. Of these, 4/7
(57%) were tested to determine their suitability to return to work with
severely immunocompromised / immunosuppressed patients, as dictated by
UK national guidance.6 The remaining 3/7 (43%) were
from HCWs tested incidentally for a second time in the asymptomatic HCW
screening programme. The median
interval between serial positive tests was 16.5 days (IQR 9.5-19.5). All
cases were attributable to prolonged SARS-CoV-2 RNA detection from a
single infection, rather than re-infection. Our approach to patients
with repeatedly positive SARS-CoV-2 PCR tests is described in the
Methods.
The fraction of positive tests amongst the HCW asymptomatic, and
HCW symptomatic and household contact screening groups combined
varied over time (Figure 1A, Table 2). In particular, during the last
two weeks of the study period (11th May to
24th May) we identified only 4 positive SARS-CoV-2
samples from 2,016 tests performed, 2 from the HCW asymptomaticand 2 from the HCW symptomatic / symptomatic household contact
arms . This fall in positive HCW tests mirrored the decline in both
patients testing positive at CUHNFT and those tested throughout the
wider region (Figure 1B). Similar trends were observed in a smaller
cohort study of HCWs in London.7