Anyone can get legionellosis, but the illness most often strikes middle-aged and older persons, especially those who smoke cigarettes or have chronic lung disease. Persons whose immune systems are weakened by cancer, kidney failure requiring dialysis, diabetes, or HIV infection are also at high risk. The main complication is respiratory failure requiring use of a respirator. Multiple organ failure and shock can lead to death. The rate is higher for persons with underlying diseases.
Pontiac fever requires no specific treatment.
Legionnaires' disease is treated with antibiotics. Treatment is started as soon as Legionnaires' disease is suspected, without waiting for test results. Erythromycin or a related antibiotic are the drugs of choice. In severe cases, a second drug, rifampin, can be added. . An estimated 15,000 to 30,000 persons get Legionnaires' disease in the United States each year.