(CNN) A person infected with measles attended a Portland Trail Blazers home game in Oregon last week amid an outbreak that has left at least 22 people ill this month in neighboring Washington state.

Contagious people also went to Portland International Airport, as well as to hospitals, schools, stores, churches and restaurants across Washington's Clark County and the two-state region, county officials said.

A public health emergency was declared Friday in Clark County, less than a half hour drive from Portland, in response to the measles outbreak.

Of 22 people with confirmed cases, 21 are children, county officials said. Eighteen had not been immunized, and it's unclear whether the remaining three were. Officials have also identified four suspected cases.

Though someone infected with measles attended the NBA game on January 11 at the Moda Center, no Oregon residents have been diagnosed with the virus, public health officials in Multnomah County, Oregon, said . But it raises the possibility the Washington outbreak could spread across the state line.

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