BACKGROUND Overcrowded housing, as well as inadequate sanitary conditions, contribute to making homeless people particularly vulnerable to the SARS-CoV-2 infection. We aimed to assess the seroprevalence of the SARS-CoV-2 infection among people experiencing homelessness on a large city-wide scale in Marseille, France, taking into account different types of accommodation. METHODS A consortium of outreach teams in 48 different locations including streets, slums, squats, emergency or transitional shelters and drop-in centres participated in the inclusion process. All participants consented to have a validated rapid antibody assay for immunoglobulins M (IgM) and G (IgG) and to answer a questionnaire on medical health conditions, comorbidities, and previous COVID-19 symptoms. Information on their housing conditions since the COVID-19 crisis was also collected from the participants. RESULTS From June 01 to August 05, 2020, 1,156 homeless participants were enrolled in the study and tested. The overall seroprevalence of SARS-CoV-2 IgG/IgM antibodies was 5.6% (95%CI 2.3-7.0), ranging from 2.2% in people living on the streets to 8.1% in people living in emergency shelters (P = 0.009). Around one third of the seropositive participants reported COVID-19 symptoms. Compared to the general population in Marseille (3.6%), the homeless population living in the same urban area experienced a significantly increased risk of SARS-CoV-2 infection (|z| = 3.65 > 1.96). CONCLUSION These findings highlight the need for regular screening among the homeless to prevent clustering in overcrowded or inadequate accommodations. It is also necessary to provide essential resources to keep homeless people healthy, the vast majority of whom have cumulative risk factors for SARS-CoV-2 infection.

中文翻译：

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无家可归者中 SARS-CoV-2 抗体的血清阳性率：在法国进行的一项基于人群的大型研究。

背景过度拥挤的住房以及卫生条件不足导致无家可归者特别容易受到 SARS-CoV-2 感染。我们的目的是评估法国马赛大范围内无家可归者感染 SARS-CoV-2 的血清阳性率，同时考虑到不同类型的住宿。方法 包括街道、贫民窟、棚屋、紧急或过渡庇护所和临时收容中心在内的 48 个不同地点的外展团队联合体参与了纳入过程。所有参与者都同意对免疫球蛋白 M (IgM) 和 G (IgG) 进行经过验证的快速抗体检测，并回答有关医疗健康状况、合并症和既往 COVID-19 症状的问卷。还从参与者那里收集了自 COVID-19 危机以来他们的住房条件的信息。结果 2020 年 6 月 1 日至 8 月 5 日，1,156 名无家可归的参与者参加了这项研究并进行了测试。SARS-CoV-2 IgG/IgM 抗体的总体血清阳性率为 5.6%（95%CI 2.3-7.0），范围从流落街头的 2.2% 到住在紧急避难所的人的 8.1%（P = 0.009）。大约三分之一的血清阳性参与者报告了 COVID-19 症状。与马赛的一般人群 (3.6%) 相比，生活在同一城市地区的无家可归者感染 SARS-CoV-2 的风险显着增加 (|z| = 3.65 > 1.96)。结论 这些发现强调了对无家可归者进行定期筛查的必要性，以防止聚集在过度拥挤或不适当的住宿环境中。