Common Risk Factors

About the Disease

Legionnaires' disease is a severe, often lethal, form of pneumonia. It's caused by the bacterium Legionella pneumophila found in both potable and nonpotable water systems. Each year, an estimated 10,000 to 18,000 people are infected with the Legionella bacteria in the United States.

It is not uncommon for patients with Legionnaires' disease to be admitted to the intensive care unit. Some will suffer long-term impaired health-related quality of life.  A study of outbreak survivors showed persistence of fatigue (75%), neurologic symptoms (66%) and neuromuscular symptoms (63%) in months after an outbreak. See Share Your Story for a first-hand account of the severity of this disease.

What are the common risk factors for Legionnaires' disease?

The most common risk factor is heavy cigarette smoking. However, chronic lung disease is also common. The most intense risk factor is organ transplantation; the medicines used to protect the new organ also compromise the patient' defense system against infection. Patients who take corticosteroid medicines are also at high risk.