At least 104 people have been sickened, with 34 hospitalized, in an outbreak of E. coli food poisoning tied to onions served on McDonald’s Quarter Pounder hamburgers, federal health officials said Wednesday.

Cases have been detected in 14 states, according to an update from the U.S. Centers for Disease Control and Prevention. One person died in Colorado and four people have developed a potentially life-threatening kidney disease complication.

Slivered onions served on the Quarter Pounders were the likely source of the outbreak, the CDC said. Taylor Farms, a California-based produce grower, recalled onions potentially linked to the outbreak. Tests by the U.S. Food and Drug Administration detected a type of E. coli bacteria that produces a dangerous toxin in one sample of the onions, but it did not match the strain that made people sick, officials reported.