Legionnaires' Disease


Legionnaires' disease is a severe bacterial infection of the respiratory tract, caused by Legionella pneumophila.


The disease acquired its name as a result of an outbreak of illness during the 1976 convention of the American Legion held in Philadelphia. At least 180 American Legion members attending the conference contracted a mysterious pneumonia that did not respond to conventional antibiotic treatment. Twenty nine people died. Eventually, the villain turned out to be Legionella pneumophila, a bacteria that was proliferating in the hotel's air conditioning system. Other outbreaks have since occurred in the U.S. and Europe.


The major environmental source of the infection is water from reservoirs and cooling units of air conditioning systems. Lakes, creeks, and areas of excavation also may harbor the bacteria. Transmission is by breathing in droplets of contaminated water. Person-to-person transmission has not been documented.

Those at risk are cigarette smokers, those with chronic lung disease, and persons receiving drugs that suppress the immune system.

Persons who have some other medical problem such as heart disease, cancer, or kidney disease are also believed to be more susceptible.


The symptoms are similar to those of many other respiratory diseases, making it difficult to differentiate and diagnose. Symptoms may include dry coughing, high fever, chills, diarrhea, shortness of breath, chest pains, headaches, excessive sweating, nausea, vomiting, and abdominal pain. Occasionally, bloody sputum is produced. Lethargy and confusion can occur in progressive, serious cases.


Although Legionnaires' disease is uncommon, it should be considered in anyone (particularly an elderly or chronically ill person) who has a respiratory tract infection that worsens over a period of about four days.

Legionnaires' disease usually makes its presence known within a week of infection. The disease can initially be mild and appear to be an episode of the flu.

The diagnosis is made from the history and physical examination, chest X ray, and bacterial culture or silver stain.


Treatment includes an antibiotic, usually erythromycin, azithromycin (Zithromax), ciprofloxacin (Cipro), or levofloxacin (Levaquin).

Hospitalization may be required.