LAS VEGAS — Nevada health authorities are investigating an outbreak of Legionnaires' disease that has been reported at the stylish 4,000-room Aria Resort and Casino on the Las Vegas Strip.

Guests who stayed at Aria Resort & Casino at Las Vegas' City Center from June 21 to July 4 may have been exposed to the bacteria that causes Legionnaires' disease, a form of pneumonia, the resort announced this week in a letter that was mailed to 18,000 guests who stayed at Aria last month. At least six guest who stayed at the resort were treated for the bacteria-borne disease.

"In cooperation with the Southern Nevada Health District, Aria Resort is contacting guests who may have stayed with us from June 21 to July 4 at a time when water tests detected elevated levels of Legionella bacteria in several of our guest rooms," reads a statement from the hotel, which has created a special website with information on the diseases. "Health officials have recently notified us of a few reported instances of guests who visited Aria, were diagnosed with, treated for and recovered from Legionnaires' disease (a form of pneumonia caused by Legionella bacteria). In an abundance of caution, we are attempting to notify guests who may have been exposed to these bacteria during this short period."

The bacteria likely were present in hot water that was distributed via showers and spas. Aria, which has in place a water treatment program, said it implemented a comprehensive abatement effort — it chlorinated and super-heated the water — as soon as initial test results were received. All subsequent tests have therefore come back with "no detectable levels" of active Legionella.

According to local TV news station KLAS-TV, no one who stayed at the hotel during the June-July time period has reported being sick. However, six people who stayed at Aria between December 2009 and April 2011 contracted Legionnaires' disease by inhaling the bacteria from the hotel's water.

The disease, which was named in 1976 when an outbreak of pneumonia spread among people attending a convention of the American Legion in Philadelphia, causes a respiratory illness that can typically be treated with antibiotics. Symptoms usually begin two to 14 days after exposure to the bacteria and include high fever, chills, cough, fatigue, muscle aches and headaches. Although the disease can be fatal — smokers, young children, the elderly and anyone with a weakened immune system are most susceptible to chronic illness — most healthy people recover from infection.

ABC World News has a story and video posted with further details and also mentions an incident that happened at the Playboy Mansion in February of this year. As many as 200 parygoers at the Mansion came down with flulike chills and high fevers.