The Denver Department of Health says three more cases of E. coli have been discovered in the past week in an outbreak believed to have started at the National Western Stock Show, bringing the total number of cases to 23.

Many of the cases are in children along the Front Range, from Boulder to El Paso County.

Several of the sick children go to day care and at least two of the cases appear to have happened after ill children came into contact with other sick children, according to the Colorado Department of Health and Environment (CDPHE).

It is unclear how the E. coli first spread at the Stock Show.