Background

Assessing the burden of COVID-19 on the basis of medically attended case numbers is suboptimal given its reliance on testing strategy, changing case definitions, and disease presentation. Population-based serosurveys measuring anti-severe acute respiratory syndrome coronavirus 2 (anti-SARS-CoV-2) antibodies provide one method for estimating infection rates and monitoring the progression of the epidemic. Here, we estimate weekly seroprevalence of anti-SARS-CoV-2 antibodies in the population of Geneva, Switzerland, during the epidemic.

Methods

The SEROCoV-POP study is a population-based study of former participants of the Bus Santé study and their household members. We planned a series of 12 consecutive weekly serosurveys among randomly selected participants from a previous population-representative survey, and their household members aged 5 years and older. We tested each participant for anti-SARS-CoV-2-IgG antibodies using a commercially available ELISA. We estimated seroprevalence using a Bayesian logistic regression model taking into account test performance and adjusting for the age and sex of Geneva's population. Here we present results from the first 5 weeks of the study.

Findings

Between April 6 and May 9, 2020, we enrolled 2766 participants from 1339 households, with a demographic distribution similar to that of the canton of Geneva. In the first week, we estimated a seroprevalence of 4·8% (95% CI 2·4–8·0, n=341). The estimate increased to 8·5% (5·9–11·4, n=469) in the second week, to 10·9% (7·9–14·4, n=577) in the third week, 6·6% (4·3–9·4, n=604) in the fourth week, and 10·8% (8·2–13·9, n=775) in the fifth week. Individuals aged 5–9 years (relative risk [RR] 0·32 [95% CI 0·11–0·63]) and those older than 65 years (RR 0·50 [0·28–0·78]) had a significantly lower risk of being seropositive than those aged 20–49 years. After accounting for the time to seroconversion, we estimated that for every reported confirmed case, there were 11·6 infections in the community.

Interpretation

These results suggest that most of the population of Geneva remained uninfected during this wave of the pandemic, despite the high prevalence of COVID-19 in the region (5000 reported clinical cases over <2·5 months in the population of half a million people). Assuming that the presence of IgG antibodies is associated with immunity, these results highlight that the epidemic is far from coming to an end by means of fewer susceptible people in the population. Further, a significantly lower seroprevalence was observed for children aged 5–9 years and adults older than 65 years, compared with those aged 10–64 years. These results will inform countries considering the easing of restrictions aimed at curbing transmission.

Funding

Swiss Federal Office of Public Health, Swiss School of Public Health (Corona Immunitas research program), Fondation de Bienfaisance du Groupe Pictet, Fondation Ancrage, Fondation Privée des Hôpitaux Universitaires de Genève, and Center for Emerging Viral Diseases.

中文翻译：

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瑞士日内瓦抗 SARS-CoV-2 IgG 抗体的血清阳性率 (SEROCoV-POP)：一项基于人群的研究。

背景

鉴于对检测策略、不断变化的病例定义和疾病表现的依赖，根据就医病例数评估 COVID-19 的负担并不理想。基于人群的血清调查测量抗严重急性呼吸综合征冠状病毒 2（抗 SARS-CoV-2）抗体，为估计感染率和监测疫情进展提供了一种方法。在这里，我们估计了疫情期间瑞士日内瓦人群中抗 SARS-CoV-2 抗体的每周血清流行率。

方法

SEROCoV-POP 研究是一项基于人群的研究，对象为 Bus Santé 研究的前参与者及其家庭成员。我们计划对之前人口代表性调查中随机选择的参与者及其 5 岁及以上的家庭成员进行一系列连续 12 周的血清调查。我们使用市售 ELISA 测试了每位参与者的抗 SARS-CoV-2-IgG 抗体。我们使用贝叶斯逻辑回归模型估计了血清流行率，同时考虑了测试表现并根据日内瓦人口的年龄和性别进行了调整。在这里，我们展示了研究前 5 周的结果。

发现

2020年4月6日至5月9日期间，我们招募了来自1339个家庭的2766名参与者，其人口分布与日内瓦州相似。第一周，我们估计血清阳性率为 4·8%（95% CI 2·4–8·0，n=341）。第二周估计值增加到 8·5% (5·9–11·4, n=469)，第三周增加到 10·9% (7·9–14·4, n=577)，6第四周为·6%（4·3–9·4，n=604），第五周为10·8%（8·2–13·9，n=775）。5-9 岁的个体（相对风险 [RR] 0·32 [95% CI 0·11–0·63]）和 65 岁以上的个体（RR 0·50 [0·28–0·78]）与 20-49 岁的人相比，血清反应呈阳性的风险显着降低。在考虑到血清转化的时间后，我们估计每报告一个确诊病例，就有 11·6 名社区感染者。

解释

这些结果表明，尽管该地区 COVID-19 的流行率很高（在 50 万人口中，不到 2·5 个月的时间内报告了 5000 例临床病例），但在这一波大流行期间，日内瓦的大部分人口仍未受到感染。 。假设 IgG 抗体的存在与免疫力有关，这些结果突显出，随着人群中易感人群的减少，疫情还远未结束。此外，与 10-64 岁的人群相比，5-9 岁儿童和 65 岁以上成人的血清阳性率显着较低。这些结果将为考虑放松旨在遏制传播的限制的国家提供信息。

资金

瑞士联邦公共卫生办公室、瑞士公共卫生学院（新冠免疫研究计划）、Fondation de Bienfaisance du Groupe Pictet、Fondation Ancrage、Fondation Privée des Hôpitaux Universitaires de Genève 和新兴病毒性疾病中心。