Iowa Department of Natural Resources looked at the 400-600 hibernating bats and saw no evidence of white-nose syndrome.
The disease prompted the state to close three caves to humans last year, including the one at Maquoketa in eastern Iowa.
It's not certain humans can spread the disease to bats, but officials didn't want to risk that possibility.
Zoologist Daryl Howell told Waterloo television station KWWL that the disease could cause the extinction of some bat species.
The disease causes a white fungus to grow on bats' muzzles and skin. It doesn't let bats hibernate, which can fatally weaken them.