SARS-CoV-2 seroprevalence and associated factors in Manaus, Brazil: baseline results from the DETECTCoV-19 cohort study

Abstract

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High anti-SARS-CoV-2 antibody seroconversion rates before the second wave in Manaus, Brazil, and the protective effect of social behaviour measures: results from the prospective DETECTCoV-19 cohort

“…Participants were followed up for up to 6 months, with a sample collection every 8–12 weeks, as previously described. 10 Visit 1 occurred between Aug 19 and Oct 2, 2020, and visit 2 between Oct 19 and Nov 27, 2020. For the baseline study, a sample size of 2399 individuals was calculated, such that the binomial 95% CI around the point estimate of antibody test positivity was less than ±2%.…”

“…For the baseline study, a sample size of 2399 individuals was calculated, such that the binomial 95% CI around the point estimate of antibody test positivity was less than ±2%. 10 …”

“…An indirect ELISA-based serological assay was used to measure anti-SARS-CoV-2 nucleocapsid IgG antibody titres in serum samples, using recombinant full-length SARS-CoV-2 nucleocapsid protein (residues 1–419, GenBank QHD43423.2) expressed in Escherichia coli cells and purified by affinity and size exclusion chromatography, as previously described. 10 The sensitivity and specificity of the assay were determined using serum samples from patients who were SARS-CoV-2 RT-PCR-positive (n=293, 87 outpatients and 113 inpatients) and from pre-pandemic controls (n=229). The assay had a sensitivity of 89·07% (95% CI 84·79–92·30) for patients at least 7 days after onset and 94·28% (89·44–97·07) for patients at least 14 days after onset of COVID-19 symptoms.…”

“…All samples with an RI value above 1 · 5 (the assay cutoff) were considered positive for anti-SARS-CoV-2 nucleocapsid IgG antibodies. 10 …”

“…In our baseline cross-sectional assessment during August, 2020, we observed that seropositivity was associated with unfavourable socioeconomic status and household clustering, as previously reported. 7 , 10 In this study, we estimated the incidence and risk factors associated with SARS-CoV-2 seroconversion from the DETECTCoV-19 cohort before the start of the second wave of infections in Manaus.…”