Prevalence evolution of SARS-CoV-2 infection in the Municipality of Sao Paulo, 2020 - 2021

Objectives: To estimate the evolution of the prevalence of SARS-CoV-2 virus infection among residents aged 18 years or over in the municipality of Sao Paulo. Methods: This is a population-based household survey conducted every 15 days, between June and September 2020 and January and February 2021. In total, 11 phases were performed. The presence of antibodies against SARS-CoV-2 was identified in venous blood using a lateral flow test, Wondfo Biotech. In the last phase, it was combined with an immunoenzymatic test, Euroimmun. Participants also answered a semi-structured questionnaire on sociodemographic and economic factors and social distancing measures. Prevalence estimates and 95% confidence intervals were estimated according to the region, Human Development Index, sex, age group, ethnicity, education, income and variables associated with risk or prevention of the infection. To compare the frequencies among the categories of each variable, the chi-square test with Rao Scott correction was used, considering a 5% significance level. Results: In total, 23,397 individuals were interviewed and had their samples collected. The estimated prevalence of antibodies against SARS-CoV-2 ranged from 9.7% (95%CI: 7.9-11.8%) to 25.0% (95%CI: 21.7-28.7). The prevalence of individuals with antibodies against SARS-CoV-2 was higher among black and pardo people, people with lower schooling, people with lower income and among residents of regions with lower Human Development Index. The lowest prevalences were associated with recommended measures of disease protection. The proportion of asymptomatic infection was 45.1%. Conclusion: The estimated prevalence of SARS-CoV-2 infection was lower than the cumulative incidence variation, except for the last phase of the study. The differences in prevalence estimates observed among subpopulations showed the social inequality as a risk of infection. The lower prevalence observed among those who could follow prevention measures reinforce the need to maintain the social distancing measures as ways to prevent SARS-CoV-2 infection.