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Notifiable Diseases On-Line


Legionellosis is a respiratory disease caused by the bacterium Legionella, which is found in a variety of natural and man-made aquatic environments, including hot water tanks, air conditioning cooling towers, humidifiers, whirlpools, spas, hot tubs and decorative fountains.The infection is acquired by inhaling airborne water droplets contaminated with the bacteria.


Legionellosis is caused by the bacterium Legionella pneumophila.


Legionellosis has been identified in North America as well as Europe, Australia, Africa and South America. Sporadic cases and outbreaks are recognized more commonly in the summer and fall.


Legionellosis has two distinct clinical and epidemiologic manifestations: Legionnaires' disease and Pontiac fever. Both are characterized by headache, myalgia (pain in one or more muscle groups), loss of appetite and a general sense of not feeling well. The spectrum of Legionaires' disease is broad and ranges from mild cases with no or few symptoms to a rapidly progressive pneumonia and sometimes death.

Pontiac fever is not associated with pneumonia or death. Patients recover spontaneously in 2 to 5 days without treatment.


Person-to-person transmission has not been documented.


Inhalation of waterborne droplets contaminated with Legionella is believed to be the primary mechanism of entry into a person's respiratory tract. The organism has been isolated from hot water systems (showers), air-conditioning cooling towers, evaporative condensers, humidifiers, whirlpool spas, respiratory therapy devices, decorative fountains, hot and cold water taps, hot tubs, creeks and ponds and the soil from their banks. Factors that facilitate the growth of the bacteria include temperatures of 25-40o C, stagnation, scale and sediment. A person's risk of acquiring legionellosis after exposure to contaminated water depends on a number of factors: the type and intensity of the exposure, and the exposed person's health status. People who have a severely impaired immune system or chronic underlying illness are at markedly increased risk for legionellosis. Those with diabetes or chronic lung disease, those who smoke cigarettes, and the elderly are at moderately increased risk of infection.


  1. Taps and shower heads should be cleaned frequently; built-up scale and sediment should be completely removed.
  2. Spas and hot tubs should be cleaned frequently.
  3. Air-cooled condenser type air conditioners are preferable over water-cooled condensers because they do not contribute to the airborne spread of the Legionella bacteria. If it is necessary to use a water-cooled condenser, clean it often with solution.
  4. Distilled water should be used in respiratory devices; the device should be cleaned on a regular basis.
  5. Hot water systems should be maintained at temperatures higher than 50o C.