[COVID 19 infection: age-stratified population-based cohort seroepidemiological study in Asunción and Central].

Background: COVID-19, caused by the severe acute respiratory syndrome virus type-2 (SARS-CoV-2), was declared a pandemic in March 2020. Seroprevalence studies are useful to estimate the proportion of the population previously infected, quantify the magnitude of transmission, estimate the fatality rate, evaluate the effect of interventions, and estimate the degree of immunity of the population.

Aim: To determine the extension of the infection and the cumulative incidence of age-specific infection, determined by seropositivity in the population of the sanitary regions of Asunción and the Central Department of Paraguay.

Methods: Population-based cohort study. In Asunción 126 households and in the Central Department 609 were surveyed between December 2020 to March 2021. Three visits were made to the selected households.

Results: The testing rate was 66.6%, 1,699 people (324 in Asunción and 1,375 in Central) of the 2,553 people registered. In the first, second and third rounds, seroprevalences were 15.5%, 15.4% and 14.3% in Asunción, respectively; in Central 23.1%, 27.8% and 26.9%, respectively. There was a seroconversion between the first and second rounds of 5.9%, and in the third round 6.5%; the accumulated global seroprevalence was 26.9% (95% CI: 24.8-19.1); in Asunción 23.1% (95% CI: 18.9-28.0) and in Central 27.8% (95% CI: 25.5-30.2). 8.5% of the participants reported symptoms; of them, 54.2% had positive serology.

Conclusion: The sero-prevalence was high with a low proportion of people with symptoms.