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.

SARS-CoV-2 seroprevalence trends in healthy blood donors during the COVID-19 outbreak in Milan / L. Valenti, A. Bergna, S. Pelusi, F. Facciotti, A. Lai, M. Tarkowski, A. Lombardi, A. Berzuini, F. Caprioli, L. Santoro, G. Baselli, C.D. Ventura, E. Erba, S. Bosari, M. Galli, G. Zehender, D. Prati. - In: BLOOD TRANSFUSION. - ISSN 2385-2070. - 19:3(2021 Jun), pp. 181-189.

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

L. Valenti
Co-primo
;
A. Bergna
Co-primo
;
S. Pelusi;A. Lai;M. Tarkowski;A. Lombardi;F. Caprioli;G. Baselli;C.D. Ventura;E. Erba;S. Bosari;M. Galli;G. Zehender;
2021-06

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.
blood donors; coronavirus; epidemiology; prevalence;
Settore MED/42 - Igiene Generale e Applicata
Settore MED/09 - Medicina Interna
Settore MED/07 - Microbiologia e Microbiologia Clinica
Settore MED/17 - Malattie Infettive
Settore MED/12 - Gastroenterologia
3-feb-2021
Article (author)
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/2434/841934
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