Las Vegas Sands’ newest Macau casino is grappling with a potentially dangerous outbreak of Legionnaires’ Disease.

Late Saturday night, Macau’s Health Bureau issued a notice saying it was investigating three cases in which Hong Kong residents reportedly contracted the potentially fatal variety of pneumonia after visits to the Parisian Macao in December 2016, January 2017 and March 2017.

The three men, whose ages range from 66 to 84 years old, were diagnosed in hospital in Hong Kong. One has since been discharged, while one man is in serious condition and the other is listed as critical.

The disease is primarily spread through inhaling warm water mist containing the bacteria. As a precautionary measure, Macau’s Health Bureau has ordered Sands China to shut the Parisian’s swimming pool, jacuzzi and fountain, while ensuring the operators conduct a thorough cleaning and disinfection of the property’s tap water system.