Abstract
Introduction: 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. Methods: We searched for SARS-CoV-2 IgGs in the 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 multivariable logistic regression models. Results: Out of the 4143 participants, 918 (22·2%) showed an RICT IgG positivity. In multivariable analysis, IgG positivity increases with age, with a significant non-linear effect (p=0·0404). We found 22 positive NPSs out of the 1330 performed. Conclusions: 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 (positive NPSs) could be found after several weeks after the epidemic peak in the area. Funding Statement: CISOM (Corpo Italiano di Soccorso dell'Ordine di Malta), FC Internazionale Milano, SFD s.p.a , Emporio Armani Olimpia Milano through donations to the Dipartimento di Scienze Biomediche e Cliniche (DIBIC) of the University of Milan and to Banca Mediolanum through donation to ASST FatebenefratelliSacco, Milano. Declaration of Interests: The authors declare no conflicts of interest. Ethics Approval Statement: The study was approved by University of Milan’s Ethical Committee.
Highlights
Is the European country in which the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) epidemic had the earliest expansion, probably starting from the last days of January [1]
The secondary objectives were to characterize the self-reported symptoms in those with and without a positive serology; to search for factors associated to SARS-CoV-2 IgG seropositivity; to assess the hospitalization rate of seropositive subjects and to estimate the infection fatality rate; and to assess the diagnostic performance of RICT when compared to chemioluminescent serological assays (CLIA)
Categorical variables are presented as total counts and percentages
Summary
Is the European country in which the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) epidemic had the earliest expansion, probably starting from the last days of January [1]. The true number of SARS-CoV-2 infections is estimated to be several times higher than the official one, mainly due to molecular testing being restricted to hospitalized and severely symptomatic cases. Recent nation-wide studies have widely different estimated seroprevalences, ranging from 1% to 6 9% in the United States [7] and 5% in Spain [8]. Lateral flow immunochromatographic tests on capillary blood (rapid immunochromatographic tests, RICT) have been proposed as point-of-care serological assays. They have been recently used in a large seroepidemiological study in Spain, demonstrating high accuracy, while having a greater uptake, lower cost, and easier implementation compared to other diagnostic methods [8]
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