At least 26 people in Colorado have become sick and one older person who lived in Mesa County with underlying health conditions has died as public health officials are warning of a suspected E. coli foodborne outbreak stemming from eating Quarter Pounders at McDonald’s.

Officials say the E. coli foodborne outbreak has been associated with multiple McDonald’s restaurants across Colorado that likely received ingredients from the same suppliers.

Colorado Department of Public Health & Environment officials are coordinating with the U.S. Centers for Disease Control and Prevention warning of a Shiga-toxin-producing E. coli foodborne outbreak associated with McDonald’s Quarter Pounders sold in multiple states, according to a CDPHE media release on Tuesday.

Currently, the 26 Colorado cases in the outbreak include residents in nine counties across the state including Routt, Arapahoe, Chaffee, El Paso, Gunnison, Larimer, Mesa, Teller and Weld.

“This is an active investigation, so we expect these numbers to change as more cases are identified,” Hope Shuler, CDPHE spokesperson said Wednesday. “The cases may not have eaten at a McDonald’s location in the county in which they reside.”

The CDC announced 49 associated cases in people who reside in 10 states, including the 26 cases in Colorado. The older person from Mesa County with underlying health conditions died after contracting E. coli, officials said.

Based on case interviews and supplier information, McDonald’s has temporarily stopped producing the food item at some locations including in Colorado. The CDC listed on Wednesday states where McDonald’s has removed slivered onions and beef patties including Colorado, Kansas, Utah and Wyoming and portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico and Oklahoma.

“Colorado cases in the outbreak reported eating at McDonald’s in late September and early October,” Shuler said. “Per McDonald’s communication to FDA, McDonald’s removed fresh slivered onions and fresh beef patties from Quarter Pounders in affected states on Oct. 22. Making this menu change should end ongoing risk.”

The CDC is coordinating a response among state public health agencies, other federal agencies and the restaurant chain. While the specific source of contamination is still under investigation, early information from the U.S. Food and Drug Administration indicates onions may be a source of this outbreak, according to the media release. Fresh-slivered onions are primarily used on Quarter Pounder hamburgers and not other McDonald’s menu items. The USDA is also looking into the beef patties on the Quarter Pounder hamburgers.

According to the CDPHE, symptoms of Shiga toxin-producing E. coli infection can include severe stomach cramps, diarrhea that is often bloody, vomiting and fever. In severe cases, hemolytic uremic syndrome may occur, which is a serious complication that can lead to kidney failure.

Anyone who recently ate a McDonald’s Quarter Pounder and is experiencing listed symptoms can contact a health care provider or public health agency.

E. coli is a bacteria commonly found in the intestines of humans and animals. While most strains are harmless, certain types, including those that are capable of producing Shiga toxins, can cause severe illness, according to the CDPHE. Most people with a Shiga toxin-producing E. coli . or STEC infection, start feeling sick three to four days after eating or drinking something that contains the bacteria. However, illness can start anywhere from one to 10 days after exposure.

The CDPHE media release suggests monitoring for symptoms and practicing good hand hygiene including washing hands thoroughly with soap and water after using the bathroom, changing diapers or before preparing food. People should not prepare food for others when experiencing diarrhea.

According to the CDC, individuals should call their healthcare provider if experiencing severe E. coli symptoms such as:

• Diarrhea and a fever higher than 102°F
• Diarrhea for more than three days that is not improving
• Bloody diarrhea
• So much vomiting a person cannot keep liquids down
• Signs of dehydration, such as not urinating much, dry mouth and throat, feeling dizzy when standing up