McDonald’s is investing $100 million (£79 million) to bring customers back to stores after an outbreak of E. coli food poisoning linked to onions on the fast food giant’s Quarter Pounder hamburgers.

The investment includes $65m (£51m) which will go directly to the most affected franchises, the company said.

The U.S. Centers for Disease Control and Prevention said sliced ​​onions on Quarter Pounders were the likely source of the E. coli. California-based Taylor Farms has recalled onions potentially linked to the outbreak.

Colorado has reported at least 30 cases; Montana reported 19; Nebraska, 13; and New Mexico, 10. Illnesses were reported between September 12 and October 21. At least 104 people became ill and 34 were hospitalized, according to federal health officials.

The Food and Drug Administration said “there does not appear to be an ongoing food safety issue related to this outbreak at McDonald’s restaurants.”

But the outbreak hurt the company’s sales.

Quarter Pounders were removed from menus in several states in the early days of the outbreak.

McDonald’s has identified an alternative supplier for the 900 restaurants that have temporarily stopped serving onion burgers. Over the past week, McDonald’s has resumed selling Quarter Pounders with sliced ​​onions nationwide.