Original article

Blood Transfusion - 3 2021 (May-June)

SARS-CoV-2 seroprevalence trends in healthy blood donors during the COVID-19 outbreak in Milan

Authors

Key words: blood donors, coronavirus, epidemiology, prevalence
Publication Date: 2021-02-03

Abstract

Background - The Milan metropolitan area in Northern Italy was among the most severely hit by the SARS-CoV-2 outbreak. The aim of this study was to examine the seroprevalence trends of SARS-CoV-2 in healthy asymptomatic adults, and the risk factors and laboratory correlates of positive tests.
Materials and methods - We conducted a cross-sectional study in a random sample of blood donors, who were asymptomatic at the time of evaluation, at the beginning of the first phase (February 24th to April 8th 2020; n=789). Presence of IgM/IgG antibodies against the SARS-CoV-2-Nucleocapsid protein was assessed by a lateral flow immunoassay.
Results - The test had a 100/98.3 sensitivity/specificity (n=32/120 positive/negative controls, respectively), and the IgG test was validated in a subset by an independent ELISA against the Spike protein (n=34, p<0.001). At the start of the outbreak, the overall adjusted seroprevalence of SARS-CoV-2 was 2.7% (95% CI: 0.3-6%; p<0.0001 vs 120 historical controls). During the study period, characterised by a gradual implementation of social distancing measures, there was a progressive increase in the adjusted seroprevalence to 5.2% (95% CI: 2.4-9.0; 4.5%, 95% CI: 0.9-9.2% according to a Bayesian estimate) due to a rise in IgG reactivity to 5% (95% CI: 2.8-8.2; p=0.004 for trend), but there was no increase in IgM+ (p=not significant). At multivariate logistic regression analysis, IgG reactivity was more frequent in younger individuals (p=0.043), while IgM reactivity was more frequent in individuals aged >45 years (p=0.002).
Discussion - SARS-CoV-2 infection was already circulating in Milan at the start of the outbreak. The pattern of IgM/IgG reactivity was influenced by age: IgM was more frequently detected in participants aged >45 years. By the end of April, 2.4-9.0% of healthy adults had evidence of seroconversion.

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Authors

Luca Valenti - Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy; Department of Transfusion Medicine and Haematology, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy

Annalisa Bergna - Department of Biomedical and Clinical Sciences “L. Sacco”, University of Milan, Milan, Italy; CRC-Coordinated Research Centre EpiSoMI-University of Milan, Milan, Italy

Serena Pelusi - Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy; Department of Transfusion Medicine and Haematology, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy

Federica Facciotti - Mucosal Immunology Laboratory, European Institute of Oncology, Milan, Italy

Alessia Lai - Department of Biomedical and Clinical Sciences “L. Sacco”, University of Milan, Milan, Italy; CRC-Coordinated Research Centre EpiSoMI-University of Milan, Milan, Italy

Maciej Tarkowski - Department of Biomedical and Clinical Sciences “L. Sacco”, University of Milan, Milan, Italy; CRC-Coordinated Research Centre EpiSoMI-University of Milan, Milan, Italy

Angela Lombardi - Department of Transfusion Medicine and Haematology, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy

Alessandra Berzuini - Department of Transfusion Medicine and Haematology, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy

Flavio Caprioli - Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy; Department of Gastroenterology, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy

Luigi Santoro - Department of Transfusion Medicine and Haematology, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy

Guido Baselli - Department of Transfusion Medicine and Haematology, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy

Carla della Ventura - Department of Biomedical and Clinical Sciences “L. Sacco”, University of Milan, Milan, Italy; CRC-Coordinated Research Centre EpiSoMI-University of Milan, Milan, Italy

Elisa Erba - Department of Transfusion Medicine and Haematology, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy

Silvano Bosari - Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy; Scientific Direction, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy

Massimo Galli - Department of Biomedical and Clinical Sciences “L. Sacco”, University of Milan, Milan, Italy; CRC-Coordinated Research Centre EpiSoMI-University of Milan, Milan, Italy

Gianguglielmo Zehender - Department of Biomedical and Clinical Sciences “L. Sacco”, University of Milan, Milan, Italy; CRC-Coordinated Research Centre EpiSoMI-University of Milan, Milan, Italy

Daniele Prati - Department of Transfusion Medicine and Haematology, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy

on behalf of Covid-19 Donors Study (CoDS) network (Appendix 1)

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