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STORY: An E. coli outbreak linked to McDonald's has killed one person and sickened dozens in the United States.

Cases were found across 10 states with most illnesses reported in Colorado and Nebraska.

The U.S. Centers for Disease Control on Tuesday said it was linked to one of the the fast food chain's most popular menu items - the Quarter Pounder.

Investigators have yet to identify the specific ingredient linked to the illness.

But they're looking into fresh, slivered onions and fresh beef patties.

The E coli. strain involved was the same as the one that killed four children in 1993, after they had eaten undercooked hamburgers at another U.S. burger chain, Jack in the Box.

U.S. food safety attorney Bill Marler, who represented a victim in that outbreak, said onions have been linked to prior cases.

McDonald's said in a statement it is temporarily removing the Quarter Pounder from restaurants in states that include Colorado, Kansas, Utah and Wyoming.

Shares of McDonald's tumbled by 6% in after-hours trade Tuesday...

A livestock trader warned U.S. cattle futures could be pressured on Wednesday too.

Symptoms for E. coli include severe stomach cramps, diarrhea and vomiting.

Most people start feeling sick three to four days after eating or drinking something that contains the bacteria, according to Colorado's public health department.

In 2015, Chipotle saw its sales battered and reputation hit due to E.coli outbreaks in several states.