Recent reports question the view that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection by means of RNA and antigen testing alone might suffice in tracking and containing the current coronavirus disease 2019 (COVID-19) pandemic [1,2]. Indeed, the transient nature of RNA testing for pathogen detection, its complexity and the described sources of inaccuracy [3] make it an incomplete metric of viral spread in a population. On the other hand, the accurate evaluation of SARS-CoV-2 specific antibodies provides not only important population-based data on pathogen exposure, on the prevalence of the infection, also in asymptomatic subjects, and on the selection of convalescent plasma donors, but also valuable information for tracking transmission dynamics, gaining knowledge on population immunity levels and informing disease control policies [4]. The paper by Perico and coworkers, published in this issue of EBioMedicine, is a comprehensive analysis of the prevalence of SARS-CoV-2 infection in the Bergamo province, an area of Italy that experienced a massive COVID-19 outbreak, with its epicenter in the whole Lombardy region. The study included 423 subjects working in two companies located in the Kilometro Rosso Scientific Park in Bergamo: the Istituto Ricerche Mario Negri and Brembo S.p.A., respectively. Health surveillance screening was offered to all workers of the two companies, with a response rate of 77%. Of the 423 subjects, 163 included in the primary study cohort tested positive at ELISA assay for SARS-CoV-2 antibodies, thus highlighting a seroprevalence of 38.5%. [5]. This percentage far exceeds not only the mean prevalence in Lombardy itself (7.5%), in Italy overall (2.5%) [6], and in other hard hit areas in the world, including New York (19.9%), London (17.5%) and Madrid (11.3%); it is also higher than the percentage (4.6%) reported in a higher risk subpopulation of healthcare workers in the Veneto region, which is relatively near to Bergamo [7]. Comparable seroprevalences have only been reported in a number of hotspots in Iran and India.
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