The contaminated ingredient is likely slivered onions, and McDonald's has pulled Quarter Pounders off the menu in 12 states in response.
An E. coli outbreak in 10 states linked to McDonald's Quarter Pounders is currently being investigated, the Centers for Disease Control and Prevention (CDC) announced on Tuesday.
There have been 49 reported illnesses connected to the outbreak, including 10 hospitalizations. One older adult in Colorado has died, and another individual developed hemolytic uremic syndrome, which can lead to kidney failure, the CDC said. The number of reported cases is expected rise, as it usually takes three to four weeks to determine whether an illness is part of a specific outbreak.
The 49 illnesses were reported between September 27 to October 11, and the CDC's investigation started on October 22. The majority of cases occurred in Colorado and Nebraska.
It is still not known which ingredient in the Quarter Pounders is making people sick, the CDC said, but preliminary findings reviewed by the Food and Drug Administration (FDA) show that slivered onions could be a "likely source of contamination."
In a press release, McDonald's said a number of the reported illnesses may be connected to onions "sourced by a single supplier that serves three distribution centers." The company has asked restaurants in this affected area to stop using the slivered onions, as well as quarter pound beef patties, until officials figure out the source of the E. coli contamination.
McDonald's also said that it was temporarily removing the Quarter Pounder from restaurants' menus in the impacted area, including Colorado, Kansas, Utah, and Wyoming, as well as certain regions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, and Oklahoma.
Other beef menu items -- such as the Big Mac and McDouble -- are not impacted.
"The decision to do this is not one we take lightly, and it was made in close consultation with the CDC," said McDonald's USA President Joe Erlinger in a video. "We are working quickly to return our full menu in these states as soon as possible."
The following states have reported cases of E. coli infection linked to the outbreak, listed by the number of illnesses:
The most common symptoms of an E. coli infection are stomach cramps, diarrhea (which is often bloody), and vomiting. Symptoms typically start three to four days after consuming the bacteria and last for about a week.
Most people recover from E. coli infections without the use of antibiotics. However, certain people have a higher chance of experiencing a more severe infection, including children under the age of five, adults 65 and older, and those with weakened immune systems. Severe symptoms might include:
If you ate a McDonald's Quarter Pounder and have severe E. coli symptoms, the CDC recommends contacting a healthcare provider.