A tragic case of E. coli infection has resulted in the death of a man in Colorado, prompting a widespread investigation by health officials.

The Centers for Disease Control and Prevention (CDC) announced on Tuesday that 49 people across ten states have been sickened by the same strain of E. coli. All affected individuals reported consuming McDonald’s products, with the majority specifically mentioning the popular Quarter Pounder.

While the exact contaminated ingredient has not been definitively identified, investigators are focusing on the slivered onions and beef patty, which have been removed from stores in the affected states.

One child has been hospitalized with hemolytic uremic syndrome (HUS), a serious kidney infection that can develop in up to one in seven E. coli patients.

Colorado has the highest number of reported cases with 27, followed by Nebraska with nine. Other states with confirmed cases include Utah, Wyoming, Kansas, Missouri, Iowa, Wisconsin, Montana, and Oregon.

E. coli bacteria are commonly found in the intestines of animals such as cattle, goats, sheep, and deer. While most strains are harmless, some can cause severe gastrointestinal symptoms, including stomach cramps, bloody diarrhea, and vomiting. The bacteria can be transmitted through contaminated food and water.

E. coli infections affect approximately 95,000 Americans annually, leading to the deaths of around 100 people. Symptoms of E. coli infection include diarrhea, fever above 102°F, vomiting, and signs of dehydration.

The CDC advises individuals who have consumed a Quarter Pounder at McDonald’s and experienced severe E. coli symptoms to seek medical attention and inform their healthcare provider of their dietary history.

HUS, which affected the hospitalized child, affects approximately 200 to 300 Americans per year and results in fatalities in less than one in twenty cases. Symptoms of HUS include bloody diarrhea, stomach cramps, fever, and vomiting.