Two people who made separate trips to Rio Las Vegas Hotel and Casino in March and April contracted Legionnaires' disease.
Mark Bergtholdt, environmental health supervisor, says the hotel began using chlorine at high temperatures on Thursday to disinfect its rooms and water system.
Health officials say environmental testing of the hotel's water system was ordered after the first illness was reported. And according to the Southern Nevada Health District and Caesars Entertainment, the testing came back positive for traces of the bacteria.
Legionnaires' disease is a respiratory disease that spreads when water droplets infected with Legionella bacteria are inhaled. Symptoms are similar to that of pneumonia, including coughing, shortness of breath, muscle aches and fever.