SARS-CoV-2 Infection During the First and Second Pandemic Waves in Spain: the ENE-COVID Study

Abstract

Objectives. To describe participant characteristics associated with severe acute respiratory syndrome coronavirus 2 infection in Spain's first 2 COVID-19 waves per the Spanish National Seroepidemiological Survey of SARS-CoV-2 Infection (ENE-COVID). Methods. A representative cohort of the noninstitutionalized Spanish population, selected through stratified 2-stage sampling, answered a questionnaire and received point-of-care testing April to June 2020 (first wave: n = 68 287); previously seronegative participants repeated the questionnaire and test November 2020 (second wave: n = 44 451). We estimated seropositivity by wave and participant characteristics, accounting for sampling weights, nonresponse, and design effects. Results. We found that 6.0% (95% confidence interval [CI] = 5.7%, 6.4%) of Spain's population was infected by June and 3.8% (95% CI = 3.5%, 4.1%) more by November 2020. Both genders were equally affected. Seroprevalence decreased with age in adults 20 years and older in the second wave; socioeconomic differences increased. Health care workers were affected at 11.1% (95% CI = 9.0%, 13.6%) and 6.1% (95% CI = 4.4%, 8.5%) in the first and second waves, respectively. Living with an infected person increased infection risk to 22.1% (95% CI = 18.9%, 25.6%) in the first and 35.0% (95% CI = 30.8%, 39.4%) in the second wave. Conclusions. ENE-COVID characterized the first 2 pandemic waves, when information from surveillance systems was incomplete. (Am J Public Health. 2023;113(5):533-544. https://doi.org/10.2105/AJPH.2023.307233).

FIGURE 1—

New Seropositive Participants for SARS-CoV-2 as Determined by the Point-of-Care Test in the (a) First and (b) Second Pandemic Waves by Province: ENE–COVID, Spain, April 27–June 22 and November 16–30, 2020 Note. ENE–COVID = Spanish National Seroepidemiological Survey of SARS-CoV-2 Infection/Estudio Nacional de Sero-Epidemiología de la Infección por SARS-CoV-2 en España; SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2. The names of all Spanish provinces outlined on the maps are provided in Appendix Figure A (available as a supplement to the online version of this article at http://www.ajph.org).

FIGURE 2—

New Seropositive Participants for SARS-CoV-2 as Determined by the Point-of-Care Test in the First and Second Pandemic Waves by Age Among (a) Men and (b) Women: ENE–COVID, Spain, April 27–June 22 and November 16–30, 2020 Note. ENE–COVID = Spanish National Seroepidemiological Survey of SARS-CoV-2 Infection/Estudio Nacional de Sero-Epidemiología de la Infección por SARS-CoV-2 en España; SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2. Vertical lines represent 95% confidence intervals.