Journal Article

Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study

Oteo, Jesús, Rodríguez-Cabrera, Francisco D., Calvo Gascón, Ana María, Lou Alcaine, María Luz, León Paniagua, José, Hernández Pascual, Montserrat, Tomás Lizcano, Aurora, Gutiérrez Fernández, Rodrigo, Limón Ramírez, Ramón, Fernández-García, Aurora, Villa Arranz, Miguel, Rubio González, Manuela, Molina, Marta, Palop Borrás, Begoña, Oliver, Antonio, Elías Retamosa, Maria Francisca, Martín, Mariano, Martín Martín, Leopoldo, Blanco, Faustino, Villafáfila Gomila, Carlos Javier, Félix de Castro, Antonio, Sanmartín, Jose L., Vázquez de la Villa, Antonia, Pérez Olmeda, María Teresa, Pérez del Campo, Dúnia, Alonso Fernández, Roberto, Marauri, Noemí, Celada Pérez, María Sagrario, Muñoz-Montalvo, Juan F., González Quintana, María Noemí, Ciruela, Pilar, Navarro Marí, José M., Iglesias Tamayo, Susana, Rodríguez-Cabrera, Francisco, Fernández-Navarro, Pablo, Cuenca-Estrella, Manuel, Cruz, Israel, Donate Suárez, Ignacio, Caro, Yolanda, Pérez-Gómez, Beatriz, Mezcua Navarro, Saturnino, Sanmartín, Jose L, Muñoz-Montalvo, Juan F, Cabrera Castro, Natalia, Ascunce Elizaga, Nieves, Elorduy Otazua,

2020

Overview

Spain is one of the European countries most affected by the COVID-19 pandemic. Serological surveys are a valuable tool to assess the extent of the epidemic, given the existence of asymptomatic cases and little access to diagnostic tests. This nationwide population-based study aims to estimate the seroprevalence of SARS-CoV-2 infection in Spain at national and regional level. 35 883 households were selected from municipal rolls using two-stage random sampling stratified by province and municipality size, with all residents invited to participate. From April 27 to May 11, 2020, 61 075 participants (75·1% of all contacted individuals within selected households) answered a questionnaire on history of symptoms compatible with COVID-19 and risk factors, received a point-of-care antibody test, and, if agreed, donated a blood sample for additional testing with a chemiluminescent microparticle immunoassay. Prevalences of IgG antibodies were adjusted using sampling weights and post-stratification to allow for differences in non-response rates based on age group, sex, and census-tract income. Using results for both tests, we calculated a seroprevalence range maximising either specificity (positive for both tests) or sensitivity (positive for either test). Seroprevalence was 5·0% (95% CI 4·7–5·4) by the point-of-care test and 4·6% (4·3–5·0) by immunoassay, with a specificity–sensitivity range of 3·7% (3·3–4·0; both tests positive) to 6·2% (5·8–6·6; either test positive), with no differences by sex and lower seroprevalence in children younger than 10 years (<3·1% by the point-of-care test). There was substantial geographical variability, with higher prevalence around Madrid (>10%) and lower in coastal areas (<3%). Seroprevalence among 195 participants with positive PCR more than 14 days before the study visit ranged from 87·6% (81·1–92·1; both tests positive) to 91·8% (86·3–95·3; either test positive). In 7273 individuals with anosmia or at least three symptoms, seroprevalence ranged from 15·3% (13·8–16·8) to 19·3% (17·7–21·0). Around a third of seropositive participants were asymptomatic, ranging from 21·9% (19·1–24·9) to 35·8% (33·1–38·5). Only 19·5% (16·3–23·2) of symptomatic participants who were seropositive by both the point-of-care test and immunoassay reported a previous PCR test. The majority of the Spanish population is seronegative to SARS-CoV-2 infection, even in hotspot areas. Most PCR-confirmed cases have detectable antibodies, but a substantial proportion of people with symptoms compatible with COVID-19 did not have a PCR test and at least a third of infections determined by serology were asymptomatic. These results emphasise the need for maintaining public health measures to avoid a new epidemic wave. Spanish Ministry of Health, Institute of Health Carlos III, and Spanish National Health System.

• Publisher: Elsevier Ltd,Elsevier B.V,Elsevier Limited
• Subject: Adolescent / Adult / Aged / Anosmia / Antibodies / Antibodies, Viral - blood / Betacoronavirus - immunology / Chemiluminescence / Child / Child, Preschool / Coastal zone / Coronavirus Infections - epidemiology / Coronaviruses / COVID-19 / Diagnostic systems / Disease hot spots / Epidemics / Epidemiology / Female / Health aspects / Households / Humans / Immunoassay / Immunoglobulin G / Immunoglobulin G - blood / Immunoglobulin M - blood / Infant / Infant, Newborn / Laboratories / Male / Microparticles / Middle Aged / Olfaction disorders / Pandemics / Pneumonia, Viral - epidemiology / Point-of-Care Testing / Population studies / Population-based studies / Prevalence / Public health / Random sampling / Risk analysis / Risk Factors / Sampling / SARS-CoV-2 / Sensitivity / Seroepidemiologic Studies / Seroepidemiology / Serological surveys / Serology / Severe acute respiratory syndrome coronavirus 2 / Sex / Spain - epidemiology / Statistical sampling / Viral diseases / Young Adult