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

Cases have been found in 10 states, with most illnesses reported in Colorado and Nebraska.

The U.S. Centers for Disease Control announced Tuesday that it was linked to one of the fast food chain’s most popular menu items – the Quarter Pounder.

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

But they’re looking for fresh, shaved onions and fresh beef patties.

The E. coli. This was the same strain as the one where four children died in 1993 after eating undercooked hamburgers at another US 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 previous cases.

McDonald’s said in a statement that it is temporarily banning the Quarter Pounder from restaurants in states including Colorado, Kansas, Utah and Wyoming.

Shares of McDonald’s plunged 6% in after-hours trading on Tuesday…

A livestock trader warned that US cattle futures could also come under pressure on Wednesday.

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

According to the Colorado Department of Public Health, most people start getting sick three to four days after eating or drinking something that contains the bacteria.

In 2015, Chipotle suffered lost sales and reputational damage due to E. coli outbreaks in several states.