The illness is very similar to pneumonia in both its symptoms and its treatment. In fact, a physician doesn't need to distinguish whether the illness is pneumonia or Legionnaires' Disease in order to treat it properly.
Symptoms typically develop two to 14 days after exposure and on the first day may include headache, muscle pain, chills and fever that could be 104 F (40 C) or higher. Coughing, shortness of breath, chest pain, fatigue, loss of appetite, gastrointestinal symptoms and confusion may follow on the second of third day.
The illness is not contagious.
Smokers and those with underlying medical conditions, including diabetes, are more susceptible, but cases have also occurred in young, otherwise healthy individuals. Those with high risk factors need to be treated promptly.
Most people who are exposed to the bacteria do not get sick, but the illness is fatal for 5 to 30 percent of those who contract it.