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Legionellosis (Legionnaires’ disease)
What is legionellosis?
Legionellosis is a lung infection caused by bacteria of the type Legionella (the majority of cases are caused by Legionella pneumophila).
The disease is contracted by inhaling fine particles of contaminated water, which can enter the lungs and then affect the immune system.
Although Legionellosis is very rare, it can be fatal, especially for people with weakened immune systems. Legionellosis is not contagious from person to person.
Causes
Bacteria of type Legionella live in water and occur naturally in the environment. They thrive at temperatures of 25 ° C to 42 ° C. They are multiplied in all types of systems involving water, for example cooling towers of air conditioning systems, water distribution systems, humidifiers or whirlpools. These devices, when poorly maintained, constitute optimal growth conditions for Legionella-type bacteria.
Legionnaire’s disease In 1976, a group of veterans of the Second World War, members of the American Legion gathered in a hotel in Philadelphia. Almost 200 of them became ill and about 30 died of pneumonia (a lung infection such as pneumonia). It was not until 2 years later, in 1978, that the bacteria responsible for this disease were identified. The Legionella pneumophila had spread through the hotel’s air conditioning system and infected several guests. Since then, Legionella has caused various outbreaks linked to air conditioning systems and water distribution networks in poorly maintained buildings in different countries. See the news: Legionellosis: the bacteria are still rife in Quebec. |
Complications
When left untreated, Legionellosis can lead to complications that can be fatal, such as:
- Respiratory failure.
- Septic shock, i.e. a sudden decrease in blood flow to vital organs following a generalized bacterial infection.
- Acute renal failure.
Mortality is less than 5% in people with intact immunity. Generally, mortality is more common in the most fragile individuals, such as the immunocompromised, the elderly or those who have had an operation.
Associated disorders
A less severe form of Legionellosis is known as Pontiac Fever. Caused by the same bacteria, Legionella pneumophila, this disease causes moderate fever, headache and muscle pain, but does not affect the lungs. This disease is not fatal and usually resolves on its own within 3 to 5 days.
Prevalence
Legionella-like bacteria are found all over the world.
According to the Public Health Agency in Canada, the prevalence of Legionellosis is approximately 75 reported cases each year, which is equivalent to 1 to 3 cases per 1 million people.1.
In France, around 1 cases of Legionella pneumonia are diagnosed each year, the incidence is estimated at 500 per 2 inhabitants per year **.
** ORPHANET data (2007)
Diagnostic
Legionellosis is a disease similar to pneumonia. The doctor may have recourse to:
- A urine test to detect the body’s immune response to the presence of Legionella bacteria.
- A sputum culture looking for Legionella bacteria.
- A blood test to identify the presence of Legionella bacteria in the blood.
- An x-ray examination of the lungs to assess the extent of the infection (in most cases).