The Aria Resort and Casino. (Courtesy Flickr user Sarah Nichols.)

The Aria Resort and Casino has released a letter explaining that the guests in questions stayed at the hotel when there were elevated levels of Legionella bacteria, which causes the disease, in the water supply.

The disease, which is similar to pneumonia, sickens between 8,000 and 18,000 people a year, according to the Centers for Disease Control. It can be serious and causes deaths in between 5 percent and 30 percent of cases. It is usually treated with antibiotics.

This is not the first outbreak this year. The disease was blamed for sickening about 200 guests of the Playboy mansion in Los Angeles, Reuters reported. A hot tub was fingered as the culprit.

The bacteria got its name from a 1976 outbreak at an American Legion convention in Philadelphia that eventually killed 34 people, the New York Times reported.