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Which bacteria cause the Legionnaire’s Disease?

Worldwide, waterborne Legionella pneumophila is the most common cause of cases including outbreaks. Legionella pneumophila and related species are commonly found in lakes, rivers, creeks, hot springs and other bodies of water. Other species including L. longbeachae can be found in potting mixes.

Legionnaire’s disease is a form of pneumonia that can be severe or even lethal. While water filtration and treatment facilities strive to make water as clean as possible before being accessible to homes and public structures. However, certain circumstances (like a specific temperature) can contribute to the proliferation of this pathogen despite any measures taken.

It can take 2 to 10 days after being exposed to the bacterium before any symptoms can appear.  Symptoms can include a feeling of weakness or tiredness, high fever and cough. Gastrointestinal stomach symptoms can also be signs of Legionnaire’s disease. In the United States, between 10,000 and 18,000 are infected with the legionella bacteria every year.

Contracting the disease

How does a person contract Legionnaire’s disease? Here is a quick look at some facts about possible disease sources that you need to be mindful of.

  1. Health experts cite the inhalation of water droplets carrying the legionella bacteria as the primary cause of the disease.
  2. Water infected with legionella bacteria that is used for drinking, brushing teeth, washing dishes, doing laundry, and other typical activities put the average person at a low risk for getting Legionnaire’s.
  3. On rare occasions when contaminated water enters a person’s airway (and eventually the lungs by accident), they can contract legionnaires disease.
  4. The bacteria can grow when water temperatures are in the range 20 – 45°C.
  5. Legionnaire’s disease is not contagious as it can only be contracted from water droplet inhalation. Consequently contact with infected persons need not be cause for concern. There is no need for people to wear face masks around infected individuals.  Pregnant women are not at risk of getting the disease from other people.
  6. Heavy cigarette smoking is one of the most common risk factors for Legionnaire’s, along with chronic lung disease and organ transplantation. People who take corticosteroid medication are also at high risk.
  7. Water distribution systems in large commercial facilities such as hotels and hospitals are major sources of the bacteria. Because transmission occurs mostly through inhalation, people should be mindful of using humidifiers, mist machines, hot springs and whirlpool spas.


Most people who fall ill with Legionnaire’s disease and are treated with the right antibiotics early on will have an excellent chance of returning to full health in a short period. Those who are hospitalised because of the disease may still experience fatigue, difficulty in concentrating, and lack of energy after being discharged. Most can expect to recover fully after a year. Smokers who get the disease are encouraged to discontinue smoking to improve the chances of proper recovery.

+Duncan Hollis