%0 Journal Article %A Paula Meireles %A Joana Amaro %A Joana Pinto da Costa %A Mariana Mendes Lopes %A Tatiana Varandas %A Pedro Norton %A João Tiago Guimarães %A Milton Severo %A Henrique Barros %T Prevalence of SARS-CoV-2 antibodies among workers of the public higher education institutions of Porto, Portugal: a cross-sectional study %D 2021 %R 10.1136/oemed-2021-107519 %J Occupational and Environmental Medicine %P 648-653 %V 78 %N 9 %X Objectives To assess the prevalence of SARS-CoV-2-specific IgM and IgG antibodies among workers of the three public higher education institutions of Porto, Portugal, up to July 2020.Methods A rapid point-of-care test for specific IgM and IgG antibodies of SARS-CoV-2 was offered to all workers (SD Biosensor STANDARD Q COVID-19 IgM/IgG Duo and STANDARD Q COVID-19 IgM/IgG Combo). Testing was performed and a questionnaire was completed by 4592 workers on a voluntary basis from 21 May to 31 July 2020. We computed the apparent IgM, IgG, and combined IgM or IgG prevalence, along with the true prevalence and 95% credible intervals (95% CrI) using Bayesian inference.Results We found an apparent prevalence of 3.1% for IgM, 1.0% for IgG and 3.9% for either. The estimated true prevalence was 2.0% (95% CrI 0.1% to 4.3%) for IgM, 0.6% (95% CrI 0.0% to 1.3%) for IgG, and 2.5% (95% CrI 0.1% to 5.3%) for IgM or IgG. A SARS-CoV-2 molecular diagnosis was reported by 21 (0.5%) workers; and of these, 90.5% had a reactive IgG result. Seroprevalence was higher among those reporting contacts with confirmed cases, having been quarantined, having a previous molecular negative test or having had symptoms.Conclusions The seroprevalence among workers from the three public higher education institutions of Porto after the first wave of the SARS-CoV-2 infection was similar to national estimates for the same age working population. However, the estimated true seroprevalence was approximately five times higher than the reported SARS-CoV-2 infection based on a molecular test.Data may be obtained from a third party upon reasonable request sent to saude.ocupacional@ispup.up.pt. %U https://oem.bmj.com/content/oemed/78/9/648.full.pdf