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.