The Centers for Disease Control and Prevention and the Food and Drug Administration announced Tuesday that multiple community health agencies are investigating an E. coli outbreak linked to Quarter Pounder burgers sold at McDonald’s across 10 states.

The CDC said there have been at least 49 people sickened across 10 states, with 10 people requiring hospitalization and one death. The Colorado Department of community Health identified that the one death occurred in the state and was an “older person with underlying conditions.”

The CDC said that the contaminated ingredient had yet to be identified, but McDonald’s said in a statement Tuesday that an initial investigation found “a subset of illnesses” were tied to the slivered onions from a supplier that serves three of the quick-food giant’s distribution centers.

“FDA is working quickly to confirm that these onions are a source of this outbreak and to determine if these onions were served or sold at other businesses,” the FDA said in its Tuesday update.

Here’s where the E. coli outbreak linked to Quarter Pounders has left people ill.

E. coli outbreak chart

States with reported E. coli illnesses as of Oct. 22

The CDC reported Tuesday that illnesses had occurred in the following states:

• Colorado
• Iowa
• Kansas
• Montana
• Missouri
• Nebraska
• Oregon
• Utah
• Wisconsin
• Wyoming

States where Quarter Pounder sales have been suspended

McDonald’s said in a statement that Quarter Pounders have been pulled from restaurants across the following states:

• Colorado
• Kansas
• Utah
• Wyoming

It has also been removed in portions of:

• Idaho
• Iowa
• Missouri
• Montana
• Nebraska
• Nevada
• recent Mexico
• Oklahoma

“We are working in close collaboration with our suppliers to replenish supply for the Quarter Pounder in the coming weeks (timing will vary by local trade),” Cesar Piña, McDonald’s North America Chief Supply Chain Officer, said in the statement noting that all other menu items were unaffected by the outbreak.

What is E. coli? What are the symptoms?

Most Escherichia coli (E. coli) bacteria reside harmlessly in the intestines of people and animals. But some can factor mild to life-threatening gastrointestinal illnesses if consumed, the CDC says.

The types of E. coli that may factor diarrhea usually spread through food or water contaminated with feces. For instance, food handlers can spread infection when they do not use proper hand washing hygiene after using the restroom. Animals such as cattle may also spread E. coli to food and food crops.

Symptoms of E. coli infection include severe stomach cramps, diarrhea (often bloody), and vomiting, according to the CDC.

The agency recommended seeking immediate medical attention if a McDonald’s customer experiences:

• Diarrhea and a fever higher than 102°F
  • Diarrhea for more than 3 days that is not improving
  • Bloody diarrhea
• So much vomiting that you cannot keep liquids down
• Signs of dehydration, such as:
  • Not peeing much
  • arid mouth and throat
  • Feeling dizzy when standing up