Prevalence and Risk Factors of SARS-CoV-2 Antibody Responses (COVID-19)

* Study design: observational and prospective study with one year of follow-up of the cohort of workers of the CSdM, including workers of subcontracted companies working in the Hospital of Mataró (2,300 workers approximately) and with controls at baseline and at 3, 6, 9 and 12 months. * Aims: to perform a universal test for all the professionals of the Consorci Sanitari del Maresme (CSdM) in order to carry out the following objectives: 1. Let them know if they have been exposed to the SARS-CoV-2 virus. 2. Identify asymptomatic carriers of SARS-CoV-2 virus. 3. Develop an immune map of all the professionals to: a) describe the seroprevalence of SARS-CoV-2 antibodies and their evolution over a year; b) help minimize the risk of infection in CSdM professionals; c) contribute to the improvement of knowledge about the infection and the social and occupational factors that affect its spread; and d) allow in the future to identify the duration of immunity against SARS-CoV-2. * Time Frame: 1 year. * Study population: all workers from the healthcare centers of the Consorci Sanitari del Maresme will be invited to participate by e-mail and by announcements in the corporate website. A space will be set up on the corporate intranet where workers will be informed about the study, will be able to give their informed consent and will be able to answer an electronic questionnaire regarding socio-demographic, clinical and labour personal characteristics. Once the questionnaire answered, participants will be authorized to schedule a blood extraction. * Methods: Prevalence of antibodies against SARS-CoV-2 will be analyzed (IgA, IgM, IgG) and PCR will be also performed for IgM and IgA positive subjects following this algorithm: Serological study: 1. Screening the entire population with total CLIA result (IgA, IgM, IgG) to determine negatives. 2. ELISA for positives with differentiated IgM, IgA and IgG results. 3. PCR of nasopharyngeal smears on all IgM and IgA + (to determine asymptomatic cases). There will be other blood samplings and determination points at 3, 6, 9 and 12 months for all the study participants.