The early and extended closure of school buildings has also heightened the risk of legionella. Legionella is the bacteria that causes Legionnaires' disease, and it has been detected in several schools near Dayton, Ohio, and in a Pittsburgh suburb. “These things happen with old buildings or buildings that aren’t used often, so, I mean, we trust the experts that they flushed the system,” parent Derek Coatney said. Officials said those guidelines, including testing and flushing water systems, can apply to schools. Hot tubs or spas that have been shut down in gyms could also be a legionella risk.