High SARS-CoV-2 seroprevalence in persons experiencing homelessness and shelter workers from a day-shelter in São Paulo, Brazil

Abstract

Brazil presents one of the highest COVID-19 death tolls in the world. The initial SARS-CoV-2 epicenter was São Paulo city. As of 2019, the homeless population of São Paulo city was estimated at 24,344 individuals, the largest national homeless population. The present study aimed to concomitantly assess the molecular and serological prevalence and associated risk factors of SARS-CoV-2 infection in a homeless population and related shelter workers from a day-shelter. Serum samples, nasopharyngeal and oropharyngeal swabs of persons who are homeless and shelter workers collected from August 25th to 27th, 2020 were tested for the presence of anti-SARS-CoV-2 IgM and IgG antibodies by ELISA and SARS-CoV-2 RNA by RT-qPCR, respectively. All swab samples tested negative by RT-qPCR. Seropositivity of IgM and IgG was 5/203 (2.5%) and 111/203 (54.7%) in persons who are homeless, and 5/87 (5.7%) and 41/87 (47.1%) in shelter workers, respectively, with no statistical differences between groups. The high seroprevalence found herein indicates early environmental and urban spreading of SARS-CoV-2, associated with sociodemographic and economic vulnerability.

Fig 1. Geographical location of the shelter and distribution of homeless population as described in the latest São Paulo city survey [12].

All maps are public domain (https://www.ibge.gov.br/geociencias/downloads-geociencias.html).

Fig 2. Optical density at 450 nm obtained for the ELISA assay used to detected anti-SARS-CoV-2 IgG in persons who are homeless (n = 203) and shelter workers (n = 87) attending the Community Center of São Martinho de Lima, Mooca subregion, São Paulo, Brazil.

ELISA assay was performed as described in materials and methods. **p ≤ 0.05 (Positive IgG–individuals who are homeless versus shelter workers: p = 0.025), n.s.: not significant (Negative IgG–individuals who are homeless versus shelter workers: p = 0.901). Statistical analysis was performed using the Mann-Whitney test.

Fig 3

Number of SARS-CoV-2 new cases (upper graph, blue) and deaths (upper and bottom graphs, red) officially reported in São Paulo city, Brazil, from March 28^th (first case of SARS-CoV-2 detected in Brazil) to November 19^th, 2020, with a 7-day moving average. Days of sample collection are shown as grey bars (August 25^th to 27^th, 2020).