E. coli outbreaks linked to McDonald's Quarter Pounders in multiple states

Health officials in multiple states have linked an E. coli outbreak, the Centers for Disease Control and Prevention said Tuesday.

It is not yet known what ingredients in hamburgers make people sick. Slivered onions and quarter-pound beef patties, both of which are used specifically for quarter pounders, are on the lookout.

At least 49 people have fallen ill in 10 states. An elderly Colorado man has died.

Ten people, including a child with a kidney disease called hemolytic uremic syndrome, were hospitalized.

According to the CDC, McDonald's is working with public health officials. The fast-food chain has stopped using sleeved onions and quarter-pound beef patties in several states, the CDC said.

McDonald's released a statement Tuesday afternoon, saying that “preliminary findings from the investigation indicate that a subset of the illnesses may be linked to slivered onions used in quarter pounders and sourced by a single supplier that serves three distribution centers.”

“We will continue to work with the Centers for Disease Control and Prevention (CDC) and are committed to providing timely updates as we restore our full menu,” the statement said.

“This is a fast-moving outbreak,” Matt Wise, chief of the CDC's Outbreak Response and Prevention Branch, told NBC News.

The first case occurred on September 27. Colorado state health officials on Oct. 10 e. coli cases alerted the CDC, Wise told NBC News. The agency started the investigation on October 15.

While the overall risk to the public is low now that McDonald's has pulled the Quarter Pounder from its restaurants in the affected states, Wise said he suspects more illnesses could be reported.

The CDC said recent illnesses have not yet been reported because “it usually takes 3 to 4 weeks to determine whether an ill person is part of an outbreak.”

E. Coli infection symptoms include high fever over 102 degrees, severe abdominal pain, diarrhea and vomiting.

Of those who got sick, 16 said they ate at McDonald's before they got sick, Wise said. Twelve of them specifically said they had a quarter pounder hamburger.

The Food and Drug Administration said it was “working expeditiously to determine” whether sleeved onions were served or sold at other businesses.

Diced onions used in other McDonald's products have not been linked to the outbreak, the FDA said.

The Department of Agriculture is assisting the CDC and state health officials in the investigation.

Most cases, 27, were reported in Colorado. Nebraska reported nine patients.

Other cases are in Iowa, Kansas, Missouri, Montana, Oregon, Utah, Wisconsin and Wyoming.