E. coli outbreak linked to McDonald's Quarter Pounders, CDC says

An outbreak of E. coli has been linked to a favorite McDonald's menu item, according to the Centers of Disease Control and Prevention.

Those sickened by E. coli reported eating Quarter Pounders at McDonald's locations before falling ill, the CDC said. It was not yet clear which specific food ingredient may have been contaminated, but investigators were looking into two particular ingredients: fresh cut onions and fresh beef patties.

There had been 49 cases reported across 10 states as of Tuesday afternoon, according to the CDC. Among those cases, one person died and 10 people had been hospitalized. Most of the illnesses have been reported in Colorado (27 cases) and Nebraska (9); other cases have been reported in Wisconsin, Iowa, Missouri, Kansas, Wyoming, Utah, Montana and Oregon.

The death was an older person in Colorado. A child was among those hospitalized as well.

Quarter Pounders may be temporarily unavailable in some states as investigators work to determine which ingredient in the burgers was making people sick, the CDC said, noting that McDonald's said it had stopped using fresh cut onions and quarter-pound beef patties in several states

The Quarter Pounders are the only burgers sold by McDonald's that uses quarter-pound beef patties, according to the CDC, while the onions are primarily used for just that dish and not on other menu items.

In a statement, McDonald's said a subset of the illnesses could be linked to the slivered onions from a supplier that serves three distribution centers. All locations in the area have been told to remove the onions and distribution of all slivered onions in the impacted area was paused.

"Out of an abundance of caution, we are also temporarily removing the Quarter Pounder from restaurants in the impacted area, including Colorado, Kansas, Utah and Wyoming, as well as portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, and Oklahoma," the statement read. "We take food safety extremely seriously and it’s the right thing to do."

The fast food giant said that all other menu items, including all beef products, were unaffected and available.

Company shares dropped significantly Tuesday afternoon after news spread of the e. coli outbreak.

E. Coli symptoms

Those who have been sickened by E. coli could experience the following severe symptoms, according to the CDC:

• Diarrhea, especially if it is for more than 3 days and is not improving, and potentially bloody
• Fever higher than 102 degrees
• Vomiting, unable to keep liquids down
• Signs of dehydration, such as dry mouth and throat, feeling dizzy when standing up, and infrequent urinating
• Stomach cramps, usually starting 304 days after ingesting the bacteria

Some may develop serious kidney problems (such as hemolytic uremic syndrome, also called HUS) and could require hospitalization.

Anyone who has eaten a McDonald's Quarter Pounder and has experienced any of the systems should contact their healthcare provider, the CDC said.

This is a developing story, please check back for updates.

Jacob Pramuk of CNBC contributed to this report.