TOPEKA, Kan. (AP) — A staffer on Republican Roger Marshall’s campaign for an open U.S. Senate seat in Kansas has tested positive for the coronavirus.

Marshall’s campaign confirmed Tuesday that the staffer tested positive last week after experiencing mild symptoms and self-quarantining.

Marshall chief of staff Brent Robertson said in a statement that the unnamed staffer was exposed to the virus at a “personal” event and hasn’t had contact with the candidate Marshall since before that event.

Marshall’s comments and actions during the coronavirus pandemic have become a major issue in his race against Democrat Barbara Bollier. Her campaign said Marshall’s campaign should disclose more information.