Seroprevalence of SARS-Cov-2 in 646 professionals at the Rothschild Foundation Hospital (ProSeCoV study).

SARS-CoV-2 infection, that led to the COVID-19 pandemic, spread in Europe from February 2020 with a peak in the Paris area on April 8, 2020. By April 19, the region had treated 32,503 patients, i.e. 40% of French cases.

The Rothschild Foundation Hospital, a 152-bed establishment in Paris, admitted 143 confirmed patients for COVID-19 (SARS-CoV-2 RT-PCR positive and/or CT scan criteria) between March 16 and April 19, 2020. Sixty-eight patients were managed in Intensive Care Units (ICU), thanks to an increase in ICU bed capacity from 10 to 39 beds.

The various hygiene measures recommended by the European Center for Disease Control (ECDC), the French ministry of Health and the French Society of Anesthesia and Critical Care (SFAR) were implemented in the hospital from February 21: hospital admission screening, isolation of patients with confirmed or suspected COVID-19 infection on designated wards and circuits (medical imaging department, operating theatre, elevators) until hospital discharge, hand hygiene according to the World Health Organization guidelines, personal protective equipment for healthcare workers (HCW) in contact with COVID-19 patients (surgical or FFP2 masks for respiratory protection, disposable gown and protective goggles), use of High Efficiency Particulate Air filters (HEPA) for ventilators. An intensive training program directed towards hospital staff in close partnership with the institution's simulation team has been carried out. In addition, all staff members and visitors have to wear a surgical face mask since March 19.

The Rothschild Foundation Hospital decided to propose SARS-CoV-2 IgG serology (ELISA technique, Elecsys® Anti-SARS-CoV-2 Roche COBAS 6000) to all volunteer employees, HCW and non-HCW. As the seroconversion rate following an infection is 90% to 100% after the third week following the contamination [1], blood samples were organised 4 weeks after the end of the French lockdown (June 8 to June 22). In this context, the ProSeCov study aimed at evaluating the effectiveness of the prevention of occupational contamination by analysing the seroprevalence rate for SARS-CoV-2. The sampling was coupled with a questionnaire concerning personal history with COVID-19, risk factors for serious forms and working conditions. The results were used anonymously. According to the French law, the study was considered to be in compliance with the MR-004 conditions [2], and was approved by the institution's ethics committee (CE_20200721_10_MML). The workers were informed of the study and could refuse to participate. Fisher’s exact test was used when appropriate.

Six hundred and forty-six samples associated with a questionnaire were collected (58% of the establishment's employees). Mains results are summarised in Fig. 1 . Seventy-eight out of 646 samples had positive serology (12.1%). There was no difference in the seroconversion of HCW versus administrative workers and between HCW from COVID-19 and non-COVID-19 units.

Fig. 1

Main seroprevalence rates of employees according to SARS-CoV-2 RT-PCR status, occupational categories and working conditions (HCW: health care workers).

Although more exposed, HCW seroconversion was similar to that of administrative workers. In the same way, the seroconversion was similar in COVID-19 and non-COVID-19 HCW.

These findings tend to suggest a positive impact of the training in hygiene and protection measures carried out by HCWs. Even if non statistical significance was shown, HCWs in the best-trained units (ICU and intermediate care units) also have the lowest seroconversion rates. However, seroconversion does not prejudge the timing of infection (before or during lockdown), nor does it prejudge intra- or extrahospital contamination. Another limitation of the study is the voluntary participation, with only 58% response rate and a probable under-representation of employees with a positive SARS-CoV-2 RT-PCR. Studies conducted among HCWs have shown comparable results in Europe: 9.3% seroconversion among HCWs in Spain [3], 11% in Belgium [4], 13.7% in the NYC area, USA [5]. Otherwise, the different epidemiological conditions make comparisons difficult (different advances in the epidemic, lockdown or local health policies implemented for example). The publication of data concerning other French establishments is pending.

Conflicts of interest

The authors declare no conflicts of interest.