Legionella

Symptoms & Diagnosis


Legionellosis or Legionnaires’ disease is an infection caused by the bacterium Legionella pneumophila, which can cause pneumonia-like symptoms such as fever, chills, and a dry cough or a cough producing sputum. Some patients exhibit muscle aches, headache, fatigue, loss of appetite, and diarrhea. Diagnosis can be confirmed through special urine and blood tests. An estimated 8,000 to 18,000 people contract the disease in the U.S. each year with a high mortality rate if left untreated.

Legionella bacteria are found throughout the environment and are most prevalent in moist or aquatic conditions such as freshwater lakes, creeks, mud, and moist soil. Bacteria from samples collected during outbreak investigations are often associated with aerosolization from building water distribution systems or cooling towers serving HVAC systems.

Disease Origin


Legionnaires’ disease was first diagnosed in a 1976 incident at the Bellevue Stratford Hotel in Philadelphia, which sickened 221 people and proved fatal for 34. Outbreaks can occur throughout the year, but generally occur during the summer and early fall. Legionella can occur in many settings, but is most concerning where immuno-compromised people may be exposed to the organism. In recent years, outbreaks of Legionella pneumophila occasionally have occurred in Montgomery County extended care facilities.

The Health Department's divisions of Communicable Disease and Water Quality Management respond to notifications of outbreaks through patient surveillance, on-site outreach, environmental assessment, and water monitoring oversight. As such, we offer guidance in the links below to long-term care and assisted care facility management and other interested parties to properly prevent and control Legionella bacteria or recognize and treat Legionellosis in their respective facilities.


Helpful Resources