The survey – entitled Vulnerability and prevalence of COVID-19 in the Ile-de-France region – aims to assess COVID-19 infection rates in people experiencing extreme hardship and to evaluate the main contributing factors. It is the first such survey to be conducted in Europe to date.
“The results confirm that the spread of the virus is particularly active in overcrowded and cramped conditions, such as when several people share a room, shower and kitchen,” says Epicentre epidemiologist Thomas Roederer, who led the survey.
The 818 participants were tested at ten emergency shelters, two food distribution points and two workers' hostels located in Paris, Val d’Oise and Seine-Saint-Denis.
COVID-19 seroprevalence – the percentage of people who have been in contact with the virus and developed antibodies – was found to be extremely high in all fourteen sites. However, there were substantial variations between sites, according to the number of people present and their physical proximity. Incidence rates were from 23% to 62% in the emergency shelters; 18% and 35% in the food distribution points; and 82% and 94% in the workers’ hostels.
This compares to one in 10 people found to have SARS-COV-2 antibodies across the whole Ile-de-France region, according to a recent population-based seroprevalence survey conducted by Santé Publique France. 
The survey’s findings indicate that, with the resurgence of the virus, homeless people urgently need to be found suitable accommodation that will not put them at increased risk of catching COVID-19, says MSF.
The majority of participants said they had used preventive measures (such as frequent handwashing and wearing masks)  and followed social distancing advice. However, spending lockdown in overcrowded conditions, with shared bedrooms, kitchens and bathrooms, greatly increased the risk of transmission. This is evidenced by the fact that people temporarily housed in gymnasiums had a prevalence of the virus that was three times higher than those housed in other types of accommodation.
“With winter coming, the emergency measures implemented to provide homeless people with temporary shelter must not be allowed to contribute to forming new clusters," warns Corinne Torre, MSF head of mission for France. “Hotels and accommodation with individual living spaces, which enable the necessary precautions to be applied effectively, are far preferable to communal facilities such as gymnasiums, which should be used only as a very last resort.”
In situations where people live in very poor and overcrowded conditions, such as the two workers' hostels included in the survey, MSF recommends that authorities ensure residents are kept fully informed and have access to preventive measures, screening and medical care, regardless of their status. Given the high risk of exposure to the virus in thess types of accommodation, those people most at risk of developing severe forms of COVID-19 should be offered an alternative place to stay to keep them safe.
“Our main objective with this survey was to evaluate the intensity of virus transmission among people in very precarious situations and to help define specific preventive activities to better protect them,” says Roederer. “Today, with the increase in the number of positive COVID-19 cases in France, it also highlights the need to conduct more epidemiological studies to better define priority strategies for those people most at risk."
 : Seroprevalence of SARS-CoV-2 among adults in three regions of France following the lockdown and associated risk factors: a multicohort study, September 2020
 : 50% said they apply them most of the time, 40% sometimes and 10% never.