A severe E. coli outbreak tied to onions served with McDonald’s quarter pounders sickened dozens of people in the US, mainly in Colorado and Nebraska, and killed one, the U.S. Centers for Disease Control and Prevention said.

Ten people have been hospitalized, including a child with complications from HUS, a syndrome that damages small blood vessels and can lead to deadly clots, the agency said. Of the people who have been interviewed, all reported eating at McDonald’s before falling ill between Sept. 27 and Oct. 11, the CDC said, with most specifying a quarter pounder.