Korian said 22 residents fell ill after Friday’s evening meal at the Cheneraie care home in Lherm, 30 km south of Toulouse. Of those, five died and 15 were seriously ill and treated in hospital.
They all showed clinical signs of severe food poisoning and an internal investigation has been launched, the company added in a statement.
The home is run by Omega, which Korian bought in February this year.
Korian said the home produced all meals on site, apparently contradicting a source close to the investigation who earlier said catering operations had recently been outsourced.
Korian’s share price tumbled as much as 9 percent, its sharpest daily fall since February 2018, before recovering some losses to trade at 33.76 euros apiece at 1149 GMT.
Korian has operations in Germany, Belgium, France, Italy and Spain. In France, it manages 294 nursing homes and employs over 20,000 people, according to the company’s website.
Four deaths were initially announced by officials, and a source close to the inquiry later told AFP that a fifth person had died.
12 of the 82 residents at the site remain in serious condition.
The suspected food was a Perigord salad, which typically includes locally sourced Gésiers de canard confits.