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. 2021 Nov 22:55:78.
doi: 10.11606/s1518-8787.2021055004075. eCollection 2021.

Population-level seropositivity trend for SARS-Cov-2 in Rio Grande do Sul, Brazil

Aluísio J D Barros  1 , Cesar G Victora  1 , Ana M B Menezes  1 , Bernardo L Horta  1 , Fernando C Barros  1 , Fernando P Hartwig  1 , Gabriel D Victora  2 , Luis Paulo Vidaletti  1 , Mariângela F Silveira  1 , Marilia A Mesenburg  1   3 , Nadège Jacques  1 , Cláudio J Struchiner  4 , Flávia Roberta Brust  3 , Marinel M Dall'Agnol  5 , Ana Paula Longaray Delamare  6 , Carlos Henrique R François  7 , Maria Letícia R Ikeda  8 , Débora C P Pellegrini  9 , Cézane Priscila Reuter  10 , Shana G da Silva  11 , Odir A Dellagostin  1 , Pedro C Hallal  1
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Population-level seropositivity trend for SARS-Cov-2 in Rio Grande do Sul, Brazil

Aluísio J D Barros et al. Rev Saude Publica. .

Abstract

Objective: To describe the evolution of seropositivity in the State of Rio Grande do Sul, Brazil, through 10 consecutive surveys conducted between April 2020 and April 2021.

Methods: Nine cities covering all regions of the State were studied, 500 households in each city. One resident in each household was randomly selected for testing. In survey rounds 1-8 we used the rapid WONDFO SARS-CoV-2 Antibody Test (Wondfo Biotech Co., Guangzhou, China). In rounds 9-10, we used a direct ELISA test that identifies IgG to the viral S protein (S-UFRJ). In terms of social distancing, individuals were asked three questions, from which we generated an exposure score using principal components analysis.

Results: Antibody prevalence in early April 2020 was 0.07%, increasing to 10.0% in February 2021, and to 18.2% in April 2021. In round 10, self-reported whites showed the lowest seroprevalence (17.3%), while indigenous individuals presented the highest (44.4%). Seropositivity increased by 40% when comparing the most with the least exposed.

Conclusions: The proportion of the population already infected by SARS-Cov-2 in the state is still far from any perspective of herd immunity and the infection affects population groups in very different levels.

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Conflict of interest statement

Conflict of Interests: The authors declare no conflict of interest.

Figures

Figure 1
Figure 1. Seropositivity for the ten rounds of the EPICOVID19-RS study. Source: EPICOVID19-RS study, Brazil, 2020–21.
Figure 2
Figure 2. Mean exposure score for the ten rounds of the EPICOVID19-RS study. Source: EPICOVID19-RS study, Brazil, 2020–21.
Figure 3
Figure 3. Probability of being seropositive according to the exposure score, estimated through a logistic regression model (7.8% to 13.0%, from the lowest to the highest exposure for round 9 and from 13.5% to 21.7% for round 10). The observed percentages of seropositives for each exposure decile are presented as dots. Source: EPICOVID19-RS study, Brazil, 2020–21.
See this image and copyright information in PMC

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Grants and funding

Funding: Ministério da Saúde do Brasil (TED 012/2020 SAPS). Instituto Serrapilheira. Associação Brasileira de Saúde Coletiva. JBS Fazer o Bem Faz Bem. Banco do Estado do Rio Grande do Sul (BANRISUL). Instituto Cultural Floresta. UNIMED Porto Alegre. Iniciativa Todos pela Saúde.