McDonald's has stopped using fresh onion slices and quarter-pound beef patties in several states, according to a statement from the fast food giant. Wisconsin was not among those states on Tuesday.

The first reported illness occurred about a month ago and the outbreak largely affected Colorado and surrounding states, but has spread west to Oregon and east to Wisconsin, according to the CDC. The reported death was an older adult and occurred in Colorado, the agency said.

The CDC said it can take three to four weeks to determine whether a sick person is part of an outbreak, and the number of people infected with the bacteria is likely larger than reported because some people were treated for their illness but never stopped E. coli would be tested.