On October 22, federal health officials announced that an E. coli outbreak linked to McDonald’s Quarter Pounder burgers has resulted in at least 10 hospitalizations and one reported death.

The Centers for Disease Control and Prevention (CDC) shared that between September 27 and October 11, a total of 49 cases were reported across 10 states, with the majority of incidents occurring in Colorado and Nebraska. According to the CDC, “most” of the affected individuals had consumed the Quarter Pounder burger, and investigators are working to determine which specific ingredient may have been contaminated.

CBS reported that among the 26 patients in Colorado, one elderly individual has died. Nebraska has reported 9 illnesses, while Utah and Wyoming each reported 4 cases. Other states, including Iowa, Kansas, Missouri, Oregon, and Wisconsin, also reported cases.

In a statement on their website, McDonald’s North America Chief Supply Chain Officer Cesar Piña indicated that “preliminary investigations suggest that part of the illnesses may be related to the diced onions used in the Quarter Pounder.”

The CDC noted that McDonald’s is collaborating with federal and state public health officials and has temporarily halted the use of fresh diced onions and Quarter Pounder patties in several states, meaning these products will be unavailable for the time being.