Updated 08/21/12 - 8:40 p.m.
CHICAGO (CBS) -- Three people who stayed at a downtown hotel in the past month have contracted Legionnaires' Disease.
The people who contracted the disease were staying at the JW Marriott Chicago, 151 W. Adams St.
The three guests who came down with Legionnaire's are all from out of state. One is in a hospital, two are recovering at home. They were part of a group that was staying at the hotel in the past month.
Dr. Kathy Ritger, with the Chicago Department of Public Health, said, "They noticed among their employees, a number of people had a fever, cough, and some had developed pneumonia."
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In letters to guests, and a posting in the hotel lobby, the Marriott was telling all guests checking in about the now-remedied contamination, and offering to arrange other accommodations. They said no guests have asked to stay elsewhere.
The big task ahead for the Marriott is to contact some 8,500 guests who stayed at the hotel in the past month, to check for symptoms.
The city and hotel officials are working to notify individuals who stayed in the hotel between July 16 though Aug. 15.
Because Legionnaire's is the result of water-borne bacteria, investigators focused on sources of standing water at the hotel. The hotel drained its swimming pool, as well as its whirlpool.
Hotel general manager Catherine Murowiec said, "They came in and did water samples from various locations around those areas. They also swabbed the areas and took those results to their laboratories.
Tests were continuing on Tuesday, but initial results indicated the hotel is now safe. Health officials said they have isolated the cause of the illness and do not believe there is an ongoing risk of infection at the hotel.
"We feel like the situation has been remedied to our satisfaction, and the likely source has been identified," Ritger said.
The Chicago Health Department is urging people who are experiencing symptoms or who have been diagnosed with pneumonia to contact their doctor.
Infectious disease expert Dr. John Segreti said Legionnaire's Disease often mirrors regular pneumonia - unless a urine test is done. Symptoms include headache, high fever, chills, coughing, and chest pain.
Segreti said it's usually treatable, but not always.
"It tends to be worse in people who are elderly, people who are smokers and have underlying lung disease, people who are immune-suppressed in any way," he said.
A hotline has been set up by the Chicago Department of Public Health to answer questions from people who may have been exposed. That phone number is (312) 746-4835 and will be staffed during Monday-Friday from 8:30 a.m. to 4:30 p.m.
Marriott executive Dave Grissen said the hotel has taken all precautions to combat the spread of the disease, including draining the pool, hot tub and fountain in the hotel.
"We care deeply about the safety of our guests and employees, and want them to be fully advised of our actions to protect their health," he said in a statement.
Most people exposed to the bacteria do not become ill. Elderly people, smokers, and people with chronic lung disease or weakened immune systems are more vulnerable. The disease is not contagious and cannot be transmitted from one person to another.
Legionnaires' disease is a severe form of pneumonia, caused by a bacterium known as Legionella. It is contracted by breathing in small droplets of water contaminated with the bacteria.
At low levels of contamination, the chance of getting Legionnaires' disease from a water source is very slight. Problems can arise when high concentrations of the organism grow in water systems.
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