Seroprevalence of anti-SARS-CoV-2 antibodies in Iquitos, Loreto, Peru.

Abstract

Background: Detection of SARS-CoV-2 antibodies among people at risk is critical for understanding both the prior transmission of COVID-19 and vulnerability of the population to the continuing transmission and, when done serially, the intensity of ongoing transmission over an interval in a community. In this study, we estimated the seroprevalence of COVID-19 in a representative population-based cohort of Iquitos, one of the regions with the highest mortality rates from COVID-19 in Peru, where a devastating number of cases occurred in March 2020. Methods: We conducted a population-based study of transmission tested each participant using the COVID-19 IgG/IgM Rapid Test from Orient Gene Biotech and used survey analysis methods to estimate seroprevalence accounting for the sampling design effect and test performance characteristics. Here we report results from the baseline (13 to 18 July 2020) and the first month of follow-up (13 to 18 August 2020) study. Findings: We enrolled a total of 716 participants and estimated seroprevalence of 70.0% (95% CI: 67.0%-73.4%), a test-re-test positivity of 65% (95% CI: 61.0%-68.3%), and an incidence of new exposures of 1.8% (95% CI: 0.9%-3.2%) data that suggest that transmission is ongoing but is occurring at low levels. We observed significant differences in the seroprevalence between age groups, with participants 18 to 29 years of age having lower seroprevalence than children <12 years of age (Prevalence ratio =0.85 [PR]; 95% CI: 0.73-0.98), suggesting that children were not refractory to infection in this setting. Interpretation: Iquitos demonstrates one of the highest rates of seroprevalence of COVID-19 worldwide. Current data shows a limited case burden in Iquitos for the past seven months and suggests that these levels are sufficient to provide significant but incomplete herd immunity. Funding: Direccion Regional de Salud de Loreto, DIRESA, Loreto, Peru