Cooling towers use water evaporation to remove heat and release it into the atmosphere. If legionella bacteria is present in the water, it can be aerosolized and spread over several kilometres by the wind. Those who inhale water droplets with the bacteria may then contract the illness. It doesn't spread person-to-person. After the 2019 outbreak in Moncton where 16 contracted the severe form of pneumonia, the regional medical officer of health said he'd support more rules for building owners to try to prevent future outbreaks.