McDonald’s claims that beef patties have been ruled out as the source of the E. coli outbreak

American fast food chain McDonald’s says it will resume selling Quarter Pounder burgers next week after testing ruled out beef patties as the source of an E. coli outbreak.

As of Friday, the US Centers for Disease Control and Prevention (CDC) has confirmed 75 cases in 13 states and one death linked to an outbreak of E. coli O157 poisoning linked to hamburgers.

Last week, the company pulled the burgers from all restaurant menus in the affected areas.

McDonald’s said Sunday that it had been notified by authorities that samples of Quarter Pounder patties had tested negative for bacteria.

The company added that an analysis of information from authorities and other data suggests that the poisoning may have been linked to chopped onions from an outside supplier.

The grocery chain says about 900 restaurants that typically received chopped onions from the facility will resume selling Quarter Pounders without them.