Serum Prevalence of Antibodies Anti-SARS-Cov-2 in Healthy Subjects and in Patients With Chronic Diseases in Pre-pandemic Blood Samples

1. Title Serum prevalence of SARS-Cov-2 antibodies in pre-pandemic blood samples
2. Background The first reports of infections caused by SARS-CoV-2, a Beta Corona virus, single-stranded RNA, were released from Wuhan, China in December 2019. From there, the infection quickly spread into a pandemic form.

The clinical manifestation of the infection varies enormously, from totally asymptomatic or mildly symptomatic forms, with nonspecific and flu-like manifestations, to an acute respiratory distress syndrome which, in patients requiring hospitalization in the ICU and mechanical ventilation invasive, can lead to death. The greater severity of the course of the infection depends greatly on the general conditions of the patients, being maximum in elderly subjects and carriers of co-morbidities. Recent studies have also evaluated the association of blood groups ABO as possible biological markers of susceptibility to COVID-19, suggesting that people with blood type O have a lower chance of infection while individuals with blood type A are most at risk, and people with blood group B have the greatest complications in the event of infection.

In Italy, the first non "imported" case dates back to February 2020 in a person residing in Lombardy, in the province of Lodi. However, new evidence on subjects tested positive for the antibody assay on serum samples suggests that the virus started to circulate before the official date.

Initially, due to the sudden explosion of cases, epidemiological surveillance focused on patients related to health facilities because they were symptomatic, suspicious and high-risk contacts. Few are the data relating to asymptomatic infections or with mild non-specific and nuanced symptoms that, data from China, would quantify in about 85% of the total number of infected. Precisely on the role of person-to-person transmission in the course of asymptomatic infection and in the subclinical phases of the disease, epidemiological data are lacking despite they could prove to be very important. In fact, thanks to the availability of serological tests that identify the presence of anti-SARS-CoV-2 antibodies, it emerged that a proportion of the population was infected by the virus and developed an antibody response and that almost 30% of the people with antibodies were asymptomatic. Therefore, the understanding of the prevalence of the disease and the prevalence of the antibody response appear to be of considerable interest, as it seems to be established that asymptomatic subjects can transmit the SARS-CoV-2 infection for a period that in some cases has proved greater than 14 days.

In order to evaluate the seroprevalence of COVID-19 infection among asymptomatic subjects, thus obtaining a real estimate of the beginning of the circulation of the virus in Italy, in the present study the investigators intend to conduct specific serological tests (total antibodies) to identify the prevalence of SARS-2-CoV antibodies among healthy blood donors who went to transfusion facilities of the DIMT in Venice during the pandemic (about 2500 periodic donors who referred to the Transfusion Center in the period between May and October 2019).