Lactalis was forced to order a massive international recall of baby milk in December after it was revealed that it had made 37 babies ill in France, one in Spain and possibly one in Greece.
Now researchers at the Pasteur Institute say that the same strain made at least 25 other babies ill between 2006 and 2016 and that it is very likely to have came from the same Lactalis factory.
Since December it has emerged that the company's own tests found salmonella at the factory in Craon, northern France, but it did not withdraw its products because it did not detect the bacteria in the milk.
That raised fears that other contaminations had taken place, especially since there was another salmonella outbreak at the factory, which affected 146 children, in 2005 - the year before Lactalis bought the site.
Same salmonella in both outbreaks
The Pasteur Institute researchers have confirmed that the same strain of salmonella was behind both outbreaks.
And they have found 25 babies fell ill due to the same strain between 2006 and 2016.
They have not been able to establish whether the babies consumed Lactalis milk but say the DNA points to the Lactalis plant.
"The only scientifically possible hypothesis is that it stayed in the factory in question," researcher François-Xavier Weill told the AFP news agency.
Company CEO Emmanuel Besnier on Thursday confirmed that tests between the two outbreaks had found the same salmonella there, although not in milk.
"We can't exclude the possibility that some babies drank contaminated milk during this period," he admitted.
The company is facing several lawsuits and a legal probe over the outbreak and police raided the group's headquarters in Laval, western France, earlier this month.
It has recalled 12 million packages of the affected baby milk, under brands including Picot, Milumel and Celia, across 83 countries.