Seroprevalence and risk factors of exposure to COVID-19 in homeless people in Paris, France: a cross-sectional study.

BACKGROUND: During the COVID-19 lockdown period from March 17 to May 11, 2020, French authorities in Paris and its suburbs relocated people experiencing recurrent homelessness to emergency shelters, hotels, and large venues. A serological survey was done at some of these locations to assess the COVID-19 exposure prevalence in this group.

METHODS: We did a cross-sectional seroprevalence study at food distribution sites, emergency shelters, and workers' residences that were provided medical services by Médecins Sans Frontières in Paris and Seine-Saint-Denis in the Ile-de-France region. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody seropositivity was detected by Luciferase-Linked Immunosorbent Assay and Pseudo Neutralization Test. Sociodemographic and exposure related information was collected via a verbal questionnaire to analyse risk factors and associations with various COVID-19 symptoms.

FINDINGS: Between June 23 and July 2, 2020, 426 (52%) of 818 individuals recruited tested positive in 14 sites. Seroprevalence varied significantly by type of recruitment site (χ p<0·0001), being highest among those living in workers' residences (88·7%, 95% CI 81·8-93·2), followed by emergency shelters (50·5%, 46·3-54·7), and food distribution sites (27·8%, 20·8-35·7). More than two thirds of COVID-19 seropositive individuals (68%, 95% CI 64·2-72·2; 291 of 426) did not report any symptoms during the recall period. COVID-19 seropositivity was strongly associated with overcrowding (medium density: adjusted odds ratio [aOR] 2·7, 95% CI 1·5-5·1, p=0·0020; high density: aOR 3·4, 1·7-6·9, p<0·0001).

INTERPRETATION: These results show high exposure to SARS-CoV-2 with important variations between those at different study sites. Living in crowded conditions was the strongest factor associated with exposure level. This study underscores the importance of providing safe, uncrowded accommodation, alongside adequate testing and public health information.

FUNDING: Médecins Sans Frontières, Epicentre, Institut Pasteur's URGENCE nouveau coronavirus fund, Total Foundation.

Copyright © 2021 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY-NC-ND 4.0 license. Published by Elsevier Ltd.. All rights reserved.