I'm not sure if this is the right place to post this...

Today I got home and went to the bathroom only to freak out as a full grown yellow jacket flew out of my shower and landed ontop of my mirror. I slowly left the room and got some bug spray that only stunned him. I then trapped him under a dixie cup in the sink and quickly filled the sink with water. He drowned in like 30 seconds thankfully.

I'm really confused how he got into my house. I live right outside of Chicago, where the temperature has been in the negatives more than anything lately. We found a few (empty) wasp nests outside my house when I bought it this summer, but there were no openings into the eaves or house, and no nests found inside. I never saw a wasp outside at all since I bought my house. I have a can light in my shower that is completely flush with the ceiling, and a vent that has very narrow openings. There is no way a bug of this size squeezed through any micro opening into my bathroom. Freak occurrence? What should I do to make sure there aren't any others?