The Southern Nevada Health District reported that two guests who stayed at Caesars Palace and another who stayed at The Orleans Hotel & Casino tested positive for the disease.
Authorities stated that the Caesars Palace customers stayed at the hotel within the last 12 months.
Environmental testing did not detect Legionella bacteria, the department said, and guests who may have been exposed are being notified.
The Independent has reached out to Caesars Entertainment for comment.
The case at The Orleans Hotel & Casino follows two confirmed cases at the property earlier this year.
“Remediation of the property’s water system was conducted, and post-remediation testing did not detect Legionella bacteria,” SNHD said.
“A third guest of the property was recently identified as a case, and environmental samples have tested positive for Legionella.”
Officials say that the hotel’s owners are cooperating and it is “undergoing remediation and environmental testing to ensure elimination of the bacteria to protect the health and safety of its guests.”
David Strow, a spokesman for Boyd Gaming Corporation which owns The Orleans, said that the property had “extensive measures in place to minimize risk” to its guests.
“We were recently notified by the Southern Nevada Health District that it is investigating a case of Legionnaire’s Disease reported by a guest who stayed at the Orleans. Upon testing, legionella was not detected in the guest’s room. However, we will continue to work closely with the Health District in their investigation,” Mr Strow said.
Legionnaires’ disease is a type of pneumonia and is caused by the Legionella bacteria.
The Centers for Disease Control says that people can become infected by drinking water that contains the bacteria or breathing in mist.