Cumulative Incidence of SARS-CoV-2 Infection Within the Homeless Population: Insights From a Citywide Longitudinal Study

Background: Studies showed high prevalence of SARs-CoV-2 among homeless people in shelters, but no longitudinal studies confirmed these findings, put them into perspective, or considered homeless populations beyond shelters.  Methods: All homeless adults sleeping rough, in slums or squats, in emergency shelters or transitional accommodation in Marseille were eligible. There were two testing sessions, 3 months apart, during which each participant was tested for anti-SARS-CoV-2 antibodies and completed a face-to-face surveys. The primary outcome was the occurrence of a seroconversion event defined as a biologically confirmed SARS-CoV-2 infection. Cox proportional hazards regression models and Kaplan-Meier survival analysis with log-rank test were performed to evaluate risk factors associated with seroconversion.  Local data from a national seroprevalence survey were used for comparison between homeless people and the general population. Findings: A total of 1249 people were included. SARS-CoV-2 seroprevalence increased from 6.0% [4.7-7.3] during the first session to 18.9% [16.0-21.7] during the second one, compared to 3.0% [1.9-4.2] and 6.5% [4.5-8.7] in the general population. Factors significantly associated with an increased risk of COVID-19 infection were: having stayed in emergency shelters (1.93 [1.18 – 3.15]), being an isolated parent (1.64 [1.07-2.52]) and having contact with more than 5-15 people per day (1.84 [1.27 – 2.67]). By contrast, smoking (0.46 (0.32 – 0.65)), having financial resources (0.70 (0.51 – 0.97)) and psychiatric or addictive comorbidities (0.52 (0.32 – 0.85)) were associated with a lower risk. Interpretation: We confirm that homeless people have higher infection rates than the general population, with increased risk in emergency shelters. Funding Information: French Directorate of Health care facilities (DGOS) – research grant PHRC COVID-19 (COVID-homeless0047) Declaration of Interests: The authors declare that they have no competing interests. Ethics Approval Statement: All participants provided a written informed consent. The COVIDHomeless study was designed and carried out in compliance with the Declaration of Helsinki and with legal and regulatory provisions. It was approved by the ethics committee on May 28, 2020 (CPP IDF VI - number 44-20; ID: 2020-AO1398-31). The database was anonymized and declared to the French data protection commission (Commission Nationale de l’Informatique et des Libertes, CNIL, n°2018172v0).