Background

The city of Manaus, Brazil, has seen two collapses of the health system due to the COVID-19 pandemic. We report anti-SARS-CoV-2 nucleocapsid IgG antibody seroconversion rates and associated risk factors in Manaus residents before the second wave of the epidemic in Brazil.

Methods

A convenience sample of adult (aged ≥18 years) residents of Manaus was recruited through online and university website advertising into the DETECTCoV-19 study cohort. The current analysis of seroconversion included a subgroup of DETECTCoV-19 participants who had at least two serum sample collections separated by at least 4 weeks between Aug 19 and Oct 2, 2020 (visit 1), and Oct 19 and Nov 27, 2020 (visit 2). Those who reported (or had no data on) having a COVID-19 diagnosis before visit 1, and who were positive for anti-SARS-CoV-2 nucleocapsid IgG antibodies at visit 1 were excluded. Using an in-house ELISA, the reactivity index (RI; calculated as the optical density ratio of the sample to the negative control) for serum anti-SARS-CoV-2 nucleocapsid IgG antibodies was measured at both visits. We calculated the incidence of seroconversion (defined as RI values ≤1·5 at visit 1 and ≥1·5 at visit 2, and a ratio >2 between the visit 2 and visit 1 RI values) during the study period, as well as incidence rate ratios (IRRs) through cluster-corrected and adjusted Poisson regression models to analyse associations between seroconversion and variables related to sociodemographic characteristics, health access, comorbidities, COVID-19 exposure, protective behaviours, and symptoms.

Findings

2496 DETECTCoV-19 cohort participants returned for a follow-up visit between Oct 19 and Nov 27, 2020, of whom 204 reported having COVID-19 before the first visit and 24 had no data regarding previous disease status. 559 participants were seropositive for anti-SARS-CoV-2 nucleocapsid IgG antibodies at baseline. Of the remaining 1709 participants who were seronegative at baseline, 71 did not meet the criteria for seroconversion and were excluded from the analyses. Among the remaining 1638 participants who were seronegative at baseline, 214 showed seroconversion at visit 2. The seroconversion incidence was 13·06% (95% CI 11·52–14·79) overall and 6·78% (5·61–8·10) for symptomatic seroconversion, over a median follow-up period of 57 days (IQR 54–61). 48·1% of seroconversion events were estimated to be asymptomatic. The sample had higher proportions of affluent and higher-educated people than those reported for the Manaus city population. In the fully adjusted and corrected model, risk factors for seroconversion before visit 2 were having a COVID-19 case in the household (IRR 1·49 [95% CI 1·21–1·83]), not wearing a mask during contact with a person with COVID-19 (1·25 [1·09–1·45]), relaxation of physical distancing (1·31 [1·05–1·64]), and having flu-like symptoms (1·79 [1·23–2·59]) or a COVID-19 diagnosis (3·57 [2·27–5·63]) between the first and second visits, whereas working remotely was associated with lower incidence (0·74 [0·56–0·97]).

Interpretation

An intense infection transmission period preceded the second wave of COVID-19 in Manaus. Several modifiable behaviours increased the risk of seroconversion, including non-compliance with non-pharmaceutical interventions measures such as not wearing a mask during contact, relaxation of protective measures, and non-remote working. Increased testing in high-transmission areas is needed to provide timely information about ongoing transmission and aid appropriate implementation of transmission mitigation measures.

Funding

Ministry of Education, Brazil; Fundação de Amparo à Pesquisa do Estado do Amazonas; Pan American Health Organization (PAHO)/WHO.

中文翻译：

---

巴西马瑙斯第二波之前的高抗 SARS-CoV-2 抗体血清转换率以及社会行为措施的保护作用：来自前瞻性 DETECTCoV-19 队列的结果

背景

由于 COVID-19 大流行，巴西马瑙斯市的卫生系统发生了两次崩溃。我们报告了巴西第二波流行之前马瑙斯居民的抗 SARS-CoV-2 核衣壳 IgG 抗体血清转化率和相关危险因素。

方法

通过在线和大学网站广告将马瑙斯成年（≥18 岁）居民的便利样本招募到 DETECTCoV-19 研究队列中。当前对血清转化的分析包括 DETECTCoV-19 参与者亚组，他们在 2020 年 8 月 19 日至 10 月 2 日（访问 1）和 2020 年 10 月 19 日至 11 月 27 日（访问2）。在第 1 次访问前报告（或没有数据）诊断出 COVID-19 并且在第 1 次访问时抗 SARS-CoV-2 核衣壳 IgG 抗体呈阳性的患者被排除在外。使用内部 ELISA，在两次就诊时都测量了血清抗 SARS-CoV-2 核衣壳 IgG 抗体的反应性指数（RI；计算为样品与阴性对照的光密度比）。

发现

2496 名 DETECTCoV-19 队列参与者于 2020 年 10 月 19 日至 11 月 27 日期间返回进行随访，其中 204 人报告在首次访问前患有 COVID-19，24 人没有关于既往疾病状态的数据。559 名参与者在基线时抗 SARS-CoV-2 核衣壳 IgG 抗体呈血清阳性。在其余 1709 名基线时血清阴性的参与者中，71 名不符合血清转化的标准，因此被排除在分析之外。在其余 1638 名基线时血清阴性的参与者中，214 名在第 2 次访视时出现血清转换。 总体血清转换发生率为 13·06% (95% CI 11·52–14·79) 和 6·78% (5·61-8 ·10) 对于有症状的血清转换，中位随访时间为 57 天 (IQR 54-61)。估计 48·1% 的血清转化事件是无症状的。样本中富裕和受过高等教育的人口比例高于马瑙斯城市人口报告的比例。在完全调整和校正的模型中，第 2 次访视前血清转化的危险因素是家庭中有 COVID-19 病例（IRR 1·49 [95% CI 1·21–1·83]），接触时未戴口罩与患有 COVID-19 (1·25 [1·09–1·45])、放松身体距离 (1·31 [1·05-1·64]) 和有流感样症状 (1· 79 [1·23–2·59]) 或第一次和第二次就诊之间的 COVID-19 诊断 (3·57 [2·27-5·63])，而远程工作与较低的发病率 (0·74 [0·56–0·97]）。

解释

在马瑙斯出现第二波 COVID-19 之前，经历了强烈的感染传播期。一些可改变的行为增加了血清转化的风险，包括不遵守非药物干预措施，如接触时不戴口罩、放松防护措施和非远程工作。需要在高传播地区增加测试，以提供有关正在进行的传播的及时信息，并帮助适当实施传播缓解措施。

资金

巴西教育部；Fundação de Amparo à Pesquisa do Estado do Amazonas；泛美卫生组织（PAHO）/世卫组织。