What is Legionella?

Legionella are rod-shaped gram-negative bacteria with over 40 known species. These bacteria survive in free-living protozoa and within biofilms that can develop in water systems.  The first documented outbreak associated with Legionella was at the 1976 Philadelphia convention of the American Legion.  It was here that 221 attendees contracted the disease and 34 died, hints the name “Legionnaires’ disease”.

Legionellosis: Legionnaires’ Disease, Pontiac Fever and their symptoms.

Legionellosis is an infection caused by the bacterium Legionella pneumophila. The disease has two distinct forms:

  • Legionnaires’ disease, the more severe form of infection which includes pneumonia. Patients with Legionnaires’ disease usually have fever, chills, and a cough, which may be dry or may produce sputum. Some patients also have muscle aches, headache, tiredness, loss of appetite, and, occasionally, diarrhea. Laboratory tests may show that these patients’ kidneys are not functioning properly. Chest X-rays often show pneumonia. It is difficult to distinguish Legionnaires’ disease from other types of pneumonia by symptoms alone; other tests are required for diagnosis. The time between the patient’s exposure to the bacterium and the onset of illness for Legionnaires’ disease is 2 to 10 days.
  • Pontiac fever, a milder illness. Persons with Pontiac fever experience fever and muscle aches and do not have pneumonia. They generally recover in 2 to 5 days without treatment. For Pontiac fever, the exposure time is shorter, generally a few hours to 2 days.

Who is at risk?

People of any age may get Legionnaires’ disease, but the illness most often affects middle-aged and older persons, particularly those who smoke cigarettes or have chronic lung disease. Also at increased risk are persons whose immune system is suppressed by diseases such as cancer, kidney failure requiring dialysis, diabetes, or AIDS. Those that take drugs that suppress the immune system are also at higher risk.

Pontiac fever most commonly occurs in persons who are otherwise healthy.

How is Legionellosis spread?

Outbreaks of legionellosis have occurred after persons have breathed mists that come from a water source (e.g., air conditioning cooling towers, whirlpool spas, showers) contaminated with Legionella bacteria. Persons may be exposed to these mists in homes, workplaces, hospitals, or public places. Legionellosis is not passed from person to person, and there is no evidence of persons becoming infected from auto air conditioners or household window air-conditioning units.

Where is Legionella Found?

Legionella organisms can be found in many types of water systems. However, the bacteria reproduce to high numbers in warm, stagnant water (90°-105° F), such as that found in certain plumbing systems and hot water tanks, cooling towers and evaporative condensers of large air-conditioning systems, and whirlpool spas. Cases of legionellosis have been identified throughout the United States and in several foreign countries.