Prevalence of SARS-CoV-2 in an area of unrestricted viral circulation: Mass seroepidemiological screening in Castiglione d'Adda, Italy

Gabriele Pagani, Andrea Giacomelli, Federico Conti, Dario Bernacchia, Rossana Rondanin, Andrea Prina, Vittore Scolari, Arianna Rizzo, Martina Beltrami, Camilla Caimi, Cecilia Eugenia Gandolfi, Silvana Castaldi, Bruno Alessandro Rivieccio, Giacomo Buonanno, Giuseppe Marano, Cosimo Ottomano, Patrizia Boracchi, Elia Biganzoli, Massimo Galli

Research output: Contribution to journalArticlepeer-review

Abstract

Castiglione D'Adda is one of the municipalities more precociously and severely affected by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) epidemic in Lombardy. With our study we aimed to understand the diffusion of the infection by mass serological screening. We searched for SARS-CoV-2 IgGs in the entire population on a voluntary basis using lateral flow immunochromatographic tests (RICT) on capillary blood (rapid tests). We then performed chemioluminescent serological assays (CLIA) and naso-pharyngeal swabs (NPS) in a randomized representative sample and in each subject with a positive rapid test. Factors associated with RICT IgG positivity were assessed by uni- and multivariate logistic regression models. Out of the 4143 participants, 918 (22.2%) showed RICT IgG positivity. In multivariable analysis, IgG positivity increases with age, with a significant nonlinear effect (p = 0.0404). We found 22 positive NPSs out of the 1330 performed. Albeit relevant, the IgG prevalence is lower than expected and suggests that a large part of the population remains susceptible to the infection. The observed differences in prevalence might reflect a different infection susceptibility by age group. A limited persistence of active infections could be found after several weeks after the epidemic peak in the area.

Original languageEnglish
Article numbere0246513
JournalPLoS One
Volume16
Issue number2 February 2021
DOIs
Publication statusPublished - Feb 2021

ASJC Scopus subject areas

  • General

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