








key: cord-320826-o6ih2f23
authors: Blairon, Laurent; Mokrane, Saphia; Wilmet, Alain; Dessilly, Géraldine; Kabamba-Mukadi, Benoît; Beukinga, Ingrid; Tré-Hardy, Marie
title: Large-scale, molecular and serological SARS-CoV-2 screening of healthcare workers in a 4-site public hospital in Belgium after COVID-19 outbreak
date: 2020-07-31
journal: J Infect
DOI: 10.1016/j.jinf.2020.07.033
sha: 
doc_id: 320826
cord_uid: o6ih2f23

nan

We read with great interest the study of Chen Y et al., who analyzed, during the Chinese epidemic peak, the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among 105 healthcare workers (HCWs) exposed to COVID-19 patients [1] . They found 17.14% of seropositive asymptomatic or paucisymptomatic HCWs although their nasopharyngeal swab samples were SARS-CoV-2 RNA negative. Our purpose was to document at the end of the Belgium epidemic the seroprevalence of SARS-CoV-2 in HCWs exposed to COVID-19 at varying degrees and to compare these rates with those observed by other teams worldwide. Another objective was to highlight SARS-CoV-2 carriage in a priori healthy staff members to sensitize them to the need to respect individual protection measures and distancing to avoid patient contamination.

In Belgium, the COVID-19-outbreak peak was reached on 10 April 2020 [2] . At the end of May, when the epidemic spread was greatly slowed down, our management decided to offer screening tests to all staff members (n=3145), regardless of their status and function. The campaign took place from May 25 to June 19, 2020 in the network of Iris hospitals South (HIS-IZZ, Brussels, Belgium), a 550-bed public hospital spread over 4 sites. Participation was voluntary and regardless of whether the HCW had already contracted the disease or not. A questionnaire was prepared focusing on the type of service the participant works in, the practice of medical procedures potentially at risk for SARS-CoV-2 infection, its status, function and perception of being infected or not. People with COVID-19 symptoms [3] were excluded from routine screening.

On the same day, all asymptomatic HCWs who agreed to participate benefited from both serological and RT-qPCR SARS-CoV-2 tests. The quantitative analysis of IgG antibodies directed against the S1 and S2 subunits of the virus spike protein was carried out using the LIAISON®SARS-CoV-2 IgG kit (DiaSorin, Saluggia, Italy). This CLIA method was extensively evaluated in our laboratory and showed 100% sensitivity two weeks after positive qRT-PCR diagnosis using an adapted cut-off [4] . Equivocal results were confirmed by a semi-quantitative ELISA method directed against the S1 subunit spike protein (Euroimmun Medizinische Labordiagnostika, Lübeck, Germany). HCWs with a previous COVID-19 documented history and a persistent positive RT-qPCR benefited from a viral culture. Statistical analyses were carried out using MedCalc version 10.4.0.0 (MedCalc Software, Ostend, Belgium). A Pvalue <0.05 is considered statistically significant.

During the study period, 1499 staff members participated (47.7%). Table 1 [5] . Our seroprevalence result of 14.6% is closer to that reported by Chen et al [1] . To the best of our knowledge, seroprevalence in HCWs after the epidemic peak was never studied in as many participants. At the end of May, the Belgian Public Health Institute, Sciensano, assessed the seroprevalence of HCWs at 8.4% among 785 samples [6] . The difference between our results and those of Sciensano can be explained by the outbreak evolution which led to seroprevalence increase.

Unexpectedly, our screening campaign failed to identify a single new case of COVID-19 among the participants. People positive to RT-qPCR were not living-virus carriers. This confirm that molecular methods can give positive results at a distance from a documented infection with an up to 67-day delay. Seroprevalence is higher than that documented by Sciensano during the epidemic peak and higher among HCWs who worked in COVID units. This shows that it is important to re-evaluate national seroprevalence in both the general population and HCWs at the end of the outbreak, especially as SARS-CoV-2 infection may be paucisymptomatic or asymptomatic and therefore infected people might ignore their status.

High SARS-CoV-2 antibody prevalence among healthcare workers exposed to COVID-19 patients

COVID-19 Bulletin épidémiologique du 10 avril

COVID-19 diagnosis and management: a comprehensive review

First experience of COVID-19 screening of health-care workers in England

SARS-CoV-2-specific antibody detection in healthcare workers in Germany with direct contact to COVID-19 patients

COVID-19 study: 8,4% of Belgian health workers have antibodies to SARS-COV-2 n

The authors thank the general and medical managements of the Iris Hospital South for taking the lead on this massive screening; the Blood Sampling Centre, the technologists and administrative staff who contributed to the analytical, pre-analytical and post-analytical steps of the laboratory tests and all those who participated in this investigation.

Ethical statement: The study design, the procedure of results communication, the information circular and the questionnaire have been submitted to and approved by our hospital's ethics committee (ethical agreement number: CEHIS/2020-19). An informed consent form has been requested from each participant, guaranteeing anonymity of the data and requesting permission to use them for statistical analysis. Out of respect for everyone's privacy, the participant was free to not answer to certain questions.Funding: All molecular tests were supported by the federal COVID-19 platform.

