The Quarter Pounder is back on the menu this week at all McDonald’s locations following an E. coli outbreak linked to onions used in its burgers, although the company warns that “the number of cases will increase.”

The move comes after the Colorado Department of Agriculture finished testing samples taken from Quarter Pounder beef patties, finding “no detection of E. coli.” Said Cesar Piña, McDonald’s Chief Supply Chain Officer for North America.

“The issue appears to be limited to a specific ingredient and a specific geography, and we remain very confident that any contaminated product related to this outbreak has been removed from our supply chain and is not from all McDonald’s restaurants,” the company said in a statement .

But “health officials have observed that as awareness increases, more people will seek medical attention and the number of cases will increase,” the company continued. “This awareness is a good thing because it can lead people to be vigilant and connect with medical professionals.”

The US Centers for Disease Control and Prevention said there were at least 75 people sickened in 13 states, with 22 of the 75 requiring hospitalization and one death reported. The Colorado Department of Public Health identified the only death in the state as an “elderly person with underlying conditions.”

Government officials are working to identify the source of the outbreak.

Map of E. coli outbreaks

States with E. coli illnesses reported as of October 28

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

• COLORADO

• Iowa

• Kansas

• Michigan

• New Mexico

• Washington

• mountain

• Missouri

• Nebraska

• Oregon

• Utah

• Wisconsin

• Wyoming

What is E. coli? What are the symptoms?

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

Types of E. coli which can cause diarrhea usually spread through food or water contaminated with faeces. For example, food handlers can spread infection when they do not use proper hygiene to wash their hands after using the restroom. Animals such as cattle can 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 has:

• Diarrhea and fever greater than 102°F

• So much vomiting that you can’t keep fluids down

• Signs of dehydration, such as:

Fernando Cervantes Jr. is a trending news reporter for USA TODAY. Contact him at [email protected] and follow X @fern_cerv_.

This article originally appeared on USA TODAY: Where are the McDonald’s E. coli cases? See the map of cases related to the outbreak