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CHICAGO (AP) — U.S. Rep. Sean Casten of Illinois has tested positive for a breakthrough case of COVID-19, according to his office.

The suburban Chicago Democrat’s office released a statement Saturday saying Casten was fully vaccinated and had received a booster vaccine dose. He described his symptoms as “mild” and said was in isolation.

“I’m grateful for the miraculous work of our scientists and health care workers — and encourage everyone to get vaccinated, boosted, and mask up,” Casten said.

Casten, first elected in 2018, is the latest Illinois politician to test positive for COVID-19.

Last month, outgoing U.S. Rep. Bobby Rush announced he had tested positive. Days later, Illinois Lt. Gov. Juliana Stratton, who was also vaccinated, said she had tested positive.

The news comes as the state and many parts of the world are reporting record infections and hospitalizations.