COVID 19 : Seroprevalence Study of Anti SRAS-CoV-2 Antibodies in GHT Employees in Haute Bretagne (AntiCoV-HB)

The first cases of the new coronavirus disease 2019 (COVID-19) due to the SARS-CoV-2 virus
were reported in December 2019 in Wuhan, China. Since that date, a significant circulation of
the virus around the world has been observed, justifying that WHO described the situation as
pandemic on March 11.

Since the start of this epidemic, numerous clinical and fundamental studies have been
conducted to best adapt the individual management of COVID-19 cases. In parallel with this
work, it is necessary to better understand the characteristics of the epidemic in the general
population but also in the population working in healthcare settings more exposed to
SARS-CoV-2. Seroprevalence studies are therefore particularly useful in order to understand
the collective immunization rate and the factors that can explain this immunization. In the
general population, only one recent study in France, in the Oise, one of the first clusters
in France, reports a seroconversion rate of 35% in the area concerned [7]. This study used
three different tests (ELISA, S-FLOW, LIPS assays) to define seroconversion (people were
considered positive if at least one of the tests reported the presence of Anti SARS CoV 2
Antibodies).

The proportion of people infected in Brittany, estimated by modeling work, would be 1.8%
[1.1% -3.3%]. At the present time, no data exist to our knowledge on the seroprevalence of
anti SARS-CoV-2 antibodies in healthcare populations. Many serological tests are currently
being validated. The Rennes University Hospital, thanks to the support of the NOMINOE fund,
will offer all employees of the territory hospital group (GHT) Haute-Bretagne to participate
in this seroprevalence study using the serological test from the company NG-Biotech. It is a
device of the type "rapid serological diagnostic orientation test (TROD)" which can be
carried out outside medical biology laboratories by a doctor / pharmacist who is not a
biologist or a nurse. This test provides a result in about fifteen minutes. The NG-Biotech
test has a CE / IVD mark (pending opinion from the Institut Pasteur). An assessment of the
sensitivity and specificity of the test was carried out at the CHU Kremlin Bicêtre and CHU
Paul Brousse. From a sample of 101 COVID-19 patients (diagnosed by RT-PCR on nasopharyngeal
or pulmonary samples) and 50 negative controls (30 pre-pandemic sera from September and
October 2017 and 20 sera from patients tested COVID- 19 negative by RT-PCR without any
symptoms for more than 15 days) a sensitivity of 97% [88.7% - 99.4%] and a specificity of
100% [91.1% -100%] were obtained 15 days after the first signs of COVID-19 patients. If the
validity of the test is very good in this study, its main limitation is that it was carried
out with a group of COVID-19 patients who were in the vast majority hospitalized (84% of
patients) and therefore not representative of pauci or asymptomatic patients .

Consequently, given the absence of consolidated data on the immune response based on clinical
pictures, it is relevant to continue validation in a population of employees in which we wish
to carry out this seroprevalence study and where the majority of infections did not lead to
hospitalization. In addition, it is also necessary to obtain other data, in particular
concerning the inter-observer reproducibility of the test which has not yet been studied. The
need to validate the test in pauci or asymptomatic populations and to obtain reproducibility
data was underlined in the opinion of the HAS on the methods for evaluating the performance
of serological tests detecting antibodies directed against SARS-CoV -2.