This study is a nationwide population-based cohort study to investigate seropositivity for SARS-CoV-2 in the non-institutionalized Spanish population. 35,883 households were selected through a stratified two-stage sampling, with strata formed by cross-classifying the 50 Spanish provinces and the two autonomous cities. 24 households were randomly sampled within each selected census tract by the National Institute of Statistic and all residents in the household were invited to participate in the study, resulting in a selected sample of 102,562 individuals of all ages.