Trends in the prevalence of COVID-19 infection in Rio Grande do Sul, Brazil: repeated serological surveys

Abstract

COVID-19 is a disease produced by the virus SARS-CoV-2. This virus has spread quickly throughout the world, leading the World Health Organization to first classify COVID-19 as an international health emergency and, subsequently declaring it pandemic. The number of confirmed cases, as April 11, surpassed 1,700,000, but this figure does not reflect the real prevalence of COVID-19 in the population, as in many countries tests are almost exclusively performed in people with symptoms, particularly severe cases. In order to properly assess the magnitude of the problem and to contribute to the design of evidence-based policies for fighting COVID-19, one must accurately estimate the prevalence of infection in the population. The present study is aimed at estimating the prevalence of infected individuals in the state of Rio Grande do Sul, Brazil, to document how fast the infection is spreading, and to estimate the proportion of infected people who present or presented symptoms, as well as the proportion of asymptomatic infections. Four repeated serological surveys will be conducted in probability samples in nine sentinel cities every two weeks, representing all regions of the State. Tests will be performed in 4,500 participants in each survey, totaling 18,000 interviews. Interviews and tests will be conducted at the participants’ household. A rapid test for the detection of antibodies will be used; the test was validated prior to the beginning of the fieldwork.