Washington DC - US health authorities said on Wednesday that they had determined that slivered onions used by McDonald's triggered an e.Coli outbreak that sickened 90 people.

"Fresh, slivered onions served on Quarter Pounders and other menu items from McDonald's are the likely source of this outbreak," the Centers for Disease Control and Prevention said in a statement.

These particular onions were supplied by Taylor Farms, which issued a voluntary recall. McDonald's also pulled the onions.

Restaurants in a dozen US states temporarily pulled the burgers from their menus this month amid the e.Coli outbreak that had been linked to them.

The number of people sickened by the tainted vegetables now stands at 90, including 27 people who had to be hospitalized as well as an elderly man in Colorado who died.

McDonald's on Sunday said that it would resume selling its Quarter Pounder hamburgers after additional tests for e.Coli had come back negative.

The e.Coli bacterium causes symptoms such as stomach cramps, diarrhea, and vomiting that generally lasts somewhere around three to four days.

Most people infected with e.Coli recover without needing treatment but some do develop more serious complications.