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

The investments include 65 million dollars (£51 million) that will go directly to the hardest-hit franchises, the company said.

The US Centres for Disease Control and Prevention has said that sliced onions on the Quarter Pounders were the likely source of the E. coli. Taylor Farms in California recalled onions potentially linked to the outbreak.

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

The Food and Drug Administration has said that “there does not appear to be a continued food safety concern 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 identified an alternate supplier for the 900 restaurants that temporarily stopped serving the burgers with onions. Over the past week, McDonald’s resumed selling Quarter Pounders with sliced onions nationwide.