The prevalence of antibodies to SARS-CoV-2 in healthcare workers of Modena. the screening on more than 7000 subjects

ABSTRACT

Introduction:Healthcare workers (HCWs) are considered at high risk of SARS-CoV-2 infection, and during outbreak more than 30 thousand of them were infected. From April, in Emilia-Romagna Region, the screening for all HCWs has started through serological tests. In this retrospective study, we evaluated the prevalence of IgG and IgM antibodies (Abs) anti SARS-CoV-2 in HCWs affiliated to AUSL of Modena. Methods:We analysed data on asymptomatic HCWs, to assess the immunological status for the regional screening, that allows Abs to be detected every two weeks. In case of positivity to serological test, SARSCoV-2 RNA detection in nasopharyngeal/oropharingeal swab takes place by RT-PCR. Results: From 30 March to 31 May 2020, 7711 HCWs were screened using commercial immunocromatography and chemiluminescent tests to detect specific Abs IgG and IgM to SARS-CoV-2. 7361 (95.4%) were IgG and IgM negative while 350(5%) were IgG and/or IgM positive. In particular, 72 (0.9%) were IgG+ and IgM+, 233 (3%) were IgG+ and IgM-, 45 (0.6%) were IgG- A nd IgM+. At follow up, 4.6% of analyzed subjects were positive, of these 4.2% was IgG+ and only the 0.4% was IgM+. The RT-PCR performed on positive HCWs revealed that 7% of them was positive for viral RNA. Conclusions: Serological tests could bridge the gap between the disease and symptoms onset, allowing to detect both active and past infection when used as screening. Results of serological tests were influenced by several factors In asymptomatic people it is difficult to establish the moment of contact, so it is plausible that the serological tests were negative because the body hasn't had the time to develop the antibodies. Conversely, detection of a very low percentage of IgM in conjunction with high IgG levels could be due to a remote contact with the virus, but also due to a scarce sensibility of tests. Furthermore, it is more likely that the asymptomatic people develop a little or no immune reaction because they didn't developed symptoms. Although the prevalence of SARS-CoV-2 infection is low among HCWs of Modena, Abs detection could be useful to detect subjects who developed an immune response, and to understand the epidemiology of the infection.