The primary source of Legionnaires' disease that killed three people staying at a downtown Chicago hotel this summer is believed to have been fairly innocuous: the decorative fountain in the lobby.

That fountain was removed from the JW Marriott on Adams Street, and the hotel began an "an ambitious remediation plan," according to Chicago health officials, that included temporary closure of the places Legionella bacteria were found, such as the men's and women's locker rooms and the swimming pool.

City health officials said the outbreak has been contained.

But it was a textbook case of a Legionnaires' outbreak, said Trish Perl, a professor of medicine and epidemiology at Johns Hopkins University. That is why she has discouraged her employer from installing decorative water fountains at the Johns Hopkins Hospital in Baltimore. "It is an underappreciated disease, and people get really sick -- scary sick," Perl said. "Unrecognized, or if a person dawdles or is prescribed the wrong antibiotic, it can cause a very impressive pneumonia."

Although swimming pools are monitored, the water in decorative fountains is not checked by either the Chicago or Illinois health departments unless people become ill.

The city and state aren't alone. Health department representatives from two of the nation's most popular tourist states, Florida and California, also said water quality in decorative fountains is tested only with cause, not as routine.

Legionnaires' disease is not exactly a plague. The bacteria are not spread among people, and those most at risk are a relatively narrow population: the elderly, heavy smokers and those with compromised immune systems. It accounts for about 10 percent of pneumonia cases, Perl said.

Still, it can clearly be a grave and unpredictable disease, as seen in a more recent outbreak in Quebec City, which has killed at least 13 people. The source of that outbreak was traced about 10 days ago to a cooling tower in an office building.

The bacteria are most often traced to the combination of widely trafficked public places and warm water, which makes a hotel's fountain a perfect intersection. Fountains "don't always register" as a potential hazard, Perl said. "People think, 'This is soothing, this is beautiful.' Since people aren't drinking water out of it, they don't think in terms of what could happen."

Does that mean travelers should beware of Legionnaire's disease? Sort of.

Perl said it's reasonable for those with compromised immune systems to avoid the spray from decorative fountains. And if there is a known outbreak of Legionnaires', absolutely, stay away, she said. She added, however, that "it's not the first thing I would worry about while traveling."

"There's travelers' diarrhea and influenza, so many things more common and likely," she said.