More than half the people living in extreme poverty in the Paris region, in particular migrants, have been infected with the coronavirus, the French aid group Doctors Without Borders (MSF) said Tuesday.

The positivity rate stood at 55% in emergency shelters and food distribution centers where MSF carried out tests in late June and early July – compared with just 12% currently in Paris.

MSF said it was the first study in Europe to focus on a region's poorest residents, including migrants, which represented 90% of the more than 800 people tested.

"The results show an extremely high prevalence. The main reason is the conditions at shelters and being packed together, which leads to clusters" of infection, Corinne Torre of MSF told Agence France-Presse (AFP).

Authorities put hundreds of migrants in gymnasiums and other temporary shelters to get them out of makeshift camps and off the streets during the two-month nationwide lockdown from mid-March to mid-May.

And in two centers housing migrant workers, the test positivity rate reached 89%, MSF said.

The Sante Publique France health agency said the overall positivity rate for France was hovering at 5%-10% last week.

The country has again tightened social distancing rules and other restrictions for Paris and its nearest suburbs to slow the coronavirus outbreak, with all bars now closed for at least two weeks.