Next time you go on a cruise, the Centers for Disease Control have issued a health warning. You might want to reconsider soaking in the ship’s hot tub.

So far, eight cases of Legionnaires’ disease were reported from a single cruise ship, but the CDC declined to name the ship or the cruise line.

Four additional cases were reported earlier this year on a second cruise ship.

Surprisingly, the cases didn’t happen with public hot tubs on the ship — just individual stateroom hot tubs.