We read with great interest the studies by Martin and colleagues on the dynamics of
SARS-CoV-2 RT-PCR positivy and seroprevalence among high risk healthcare workers and
hospital staff (1), and Zheng and colleagues on characterisitics and transmission
dynamics of COVID-19 in healthcare workers at a London teaching hospital (2). Taken
together, these two studies underscored the efficacy of personal protective equipment
(PPE), the acquisition of infections predominantly around lockdown time, and possible
extraprofessional exposures as the source of infections. We report here a seroprevalence
study of differentially exposed healthcare workers and hospital personnel to COVID-19
patients, which showed similar results, but, in contrast, a significant increased
risk of COVID-19 in staff working in high risk COVID-19 units.
With the expansion of infections in France, authorities implemented a national lockdown
on March 17th which lasted till the 11th of May 2020. Measures implemented in our
hospital and their timeline are detailed in figure 1
. Between the 21st of April and the 3rd of June 2020, we included 647 healthcare and
hospital personnel volunteers from highly, mildly and unexposed COVID-19 units who
had physically been present during the lockdown. Highly exposed volunteers had worked
in the medical, intensive care and screening COVID-19 units, mildly exposed in the
non COVID-19 medical units, and unexposed personnel from the administration or laboratories.
For highly and mildly exposed healthcare workers, eligibility implied being in contact
with patients or their immediate environment (i.e. cleaning agents). After completing
an investigator-led questionnaire, a blood sample for serological determination was
collected, using the anti SARS-CoV-2 IgG antibobies with the ID Screen® SARS-CoV-2-N
IgG Indirect assay (ID.Vet®). Highly exposed participants had a systematic concomitant
nasopharyngeal swab for SARS-CoV-2 RT-PCR test, and in other groups only if seropositive.
Seropositive participants were investigated by two specialists to determine whether
SARS-CoV-2 acquisition was most likely professional or extraprofessional. We aimed
to include at least 156 subjects per exposure group, and to compare rates in each
group using an exact logistic regression adjusted on age, gender and profession (doctor/resident,
paramedical or other).
Figure 1
Timeline of clinical events according to implementation of barrier measures in the
13 serological positive volunteers. To better understand potential infectious dynamics,
please read the time-dependant A, B, C measures in our hospital setting. In all units,
physical presence of non-essential personnel, social distancing at work, systematic
hand sanitizing, and virtual meetings were encouraged. Professionals exposed to COVID-19
patients were specifically trained to use and discard PPE, including protective suits,
FFP2 masks, double pair of gloves, eye protective gears, shoe covers, mobcaps and
gowns.
Figure 1
We included 261 highly and 227 mildly exposed (representing 70% and 93% of the corresponding
eligible workforce respectively), and 159 unexposed volunteers. Mean age was 38.3
(SD ± 11.0), 496 (77 %) were women. Mean days of work in the highly exposed was 21.5
days (±11.0). Thirteen personnel tested positive for SARS-CoV-2 NP IgG (prevalence
rate of 2.01 % [95% Confidence Interval: 0.93-3.09]); ten people (3.91 % [1.53-6.28])
in the highly exposed group, two (0.8 % [0.0-2.1]) in the mildly exposed group and
one (0.63 % [0.00-1.86]) in the unexposed group (p = 0.022). After adjustment, the
odds ratio (OR) of being positive for SARS-CoV-2 in the highly exposed group was 4.43
(95% CI 1.15-17.06) versus mildly and unexposed groups (p = 0.031). One highly exposed
healthcare worker had a positive SARS-CoV-RT- PCR at study entry, with a positive
COVID-19 serology.
Seven seropositive cases had exposures prior or within 14 days of lockdown (figure
1). Extra professional exposure was deemed most probable for 6 cases. Four of the
seven most probable professional acquisition occurred in workers who recalled unprotected
contact with a COVID-19 case prior to full implementation of PPE in a non COVID-19
department, and in one worker from the medical COVID-19 department intermittently
using a surgical mask in presence of colleagues. Two workers did not report any known
specific exposure.
Despite an increased risk of acquiring COVID-19 in highly exposed personnal, seroprevalence
was low, reflecting efficacy of PPE and barrier procedures, in line with two non-comparative
studies carried out in highly exposed healthcare workers (3) (4). Most nosocomial
COVID-19 infections occurred at the beginning of the lockdown, a period in which recommendations
were being fully upgraded and implemented, and extraprofessional acquisition more
probable due to the high community viral circulation. It was also a time in which
medical and paramedical teams were still inexperienced and stressed, which could enhance
mistakes when using new protective gears (5). Also, some data suggests possible airborne
transmission of SARS-CoV-2 in enclosed environments, against which surgical masks
may lack efficacy (6). Our findings contrast with a Chinese study of 420 heatlthcare
professionals deployed to Wuhan for direct care of COVID-19 patients, for whom serology
and SARS-CoV-2 RT-PCR of naso-pharyngal swabs on return revealed no infection (7).
However, in this study, Liu and colleagues described full measures implemented prior
to the professionnels’ arrival, but also very strict extraprofessional rules which
may be difficult to implement in other parts of the world and over an extended period.
In conclusion, SARS-CoV-2 nosocomial transmissions to healthcare workers occur in
high risk settings, but PPE procedures are effective in reducing acquisition. Many
cases were likely due to extraprofessional exposures and incomplete compliance to
procedures. Following strict PPE procedures at work and outside are essential to reduce
nosocomial acquisition of SARS-CoV-2.
Conflict of Interest Statement: the authors report no support from any organisation
for the submitted work; no financial relationships with any organisations that might
have an interest in the submitted work in the previous three years, and no other relationships
or activities that could appear to have influenced the submitted work. Contributorship
statement: all authors contributed to the investigation, data analysis and interpretation,
and final approval of article. MB and OV realized most of the investigation and the
first draft of th article, FG, MCP, GM and AM conceived and planned the study.
The study protocol was reviewed and approved by the University Hospital of Montpellier
Institutional Review board (RB ID: 202000465), and registered on clinicalTrials.gov
under the ID: NCT04376944. All participants consented to the study procedures and
objectives. The participants were not involved in the design, or conduct, or reporting,
or dissemination plans of our research.