First identified in 1976 with a particularly virulent outbreak of pneumonia in Philadelphia, where American Legion delegates were gathered for a convention. The outbreak was caused by a previously unknown, airborne bacterium called Legionnella pneumonophilia. It can be spread via AC systems or excavation sites and has a mortality rate up to 15%.

The legionnella bacterium is actually present in water but requires a warm temperature to become active. In order to become infected the water has to be heated to the range in which legionnella is active. It must also be in an aerosol form so that the legionnella is inhaled rather than ingested.

As well as the systems mentioned by kessenich a major contributor to airborn legionnella is water towers used to cool down water from refrigeration systems. Steps are being taken to limit exposure in this manner by doping the water with biocide or by bubbling ozone through the water before cooling.

A legionnella infection (legionellosis) can take two forms, the milder illness Pontiac fever, and the more serious Legionnaires' Disease.

The Centre for Disease Control lists the symptoms of legionnellosis as being fever, chills, dry or wet cough, muscle aches, headache, tiredness, loss of appetite, and, occasionally, diarrhea. Possibility of kidneys not functioning properly. Pneumonia. All of these are symptoms of Legionnaires' Disease

Pontiac fever symptoms are reduced to fever and muscle aches

The incubation period for Legionnaires' disease is 2 to 10 days and few hours to 2 days for Pontiac fever.

Legionnaires' Disease is gnerally treated with an antibiotic.

For more detailed information try the CDC web page on Legionnaires' Disease at

Legionellosis (Legionnaires' disease)

A disease caused by the bacterium Legionella pneumophila. There are actually two flavors of the disease, the famous Legionnaires' disease, which can be fatal, and Pontiac fever, which is more mild.

The bacteria got its name after an outbreak of pneumonia occurred in attendees of an American Legion convention in Philadelphia. Several died, and the cause was traced to the bacterium. It is estimated that about 8,000 to 18,000 persons in the United States get Legionellosis every year. Although outbreaks get significant coverage, the disease usually occurs as isolated, independant cases. Those who contract Legionnaires' disease have a 5% to 30% chance of death.

Legionellosis has different symptoms, depending on the flavor. People who get Pontiac fever get it within 2 days of exposure. They experience fever and muscle aches, but not much worse. They usually recover in 2 to 5 days without treatment.

Legionnaires' is slower, and more painful. Victims usually don't show symptoms until 2 to 10 days after exposure, and can expect fever, chills, coughing fits, and sometimes also get headaches, tiredness, loss of apetite, and sometimes diarrhea. Sometiems lab tests will show that the kidneys do not function properly.

Legionnaires' is difficult to differentiate from other types of pneumonia through symptomes alone, and usually requires some other tests, such as looking for the bacteria in spit, checking the urine, and monitoring antibody count in the blood. Note that none of these tests are routine for pneumonia sufferers, so a doctor must actively suspect Legionellosis before it can be diagnosed. Legionnaires' is treated with the antibiotic erythromycin, and sometimes rifampin as well, in advanced cases. Pontiac fever is allowed to run its course.

Legionnaires' most commonly occurs in middle-aged or old people. Smoking, chronic lung disease, and immunodeficiency diseases also increase the likelihood of contracting Legionnaires'. Anyone can get Pontiac fever.

Legionella bacteria breed in warm stagnant water, and grow the fastest when the temperature is between 90 and 105 degrees F. Infection occurs when a person breathes in mist from an infected water source. This usually happens around cooling towers, spas, hot water tanks, and certain HVAC systems. Transmission has never been found from auto or home window air conditioners. It is not transmitted from person to person.

Legionellosis can only be prevented at the level of local government, by making sure that public water sources are not infected, and that plumbing systems are properly maintained. If you think that living in your area poses an unacceptable risk for Legionellosis, then either write letters to City Hall or move out.

A big shout-out goes to for the mad 411.

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