The disease :

Its name comes from an epidemic that happened in 1976 and affected 182 members of the 58th American Legion  Congress in Philadelphia; 29 of them died. The Legionella pneumophila bacteria, that thrives on warm water ( 30 to 60°C), had spread through the air-conditioning system of their hotel. The recent emergence of this disease is to be linked with its affinity with the modern water supply systems such as the cooling towers, the air conditioners, the Jacuzzis, the hot water pipeworks…

Definition

  The Legionella is a negative gram bacillus, of 0, 2 à 0, 9 µm wide, and of 2 à 20 µm long. It has a coccobacillary shape and becomes filamentous when cultivated, strict aerobic, and moves thanks to one or several flagellums. It develops optimally in a temperature margin between 20 and 45°C. In a natural environment, the legionellae have to find a protection against unfavourable environmental living conditions : either by living as a parasite on some unicellular eukaryote beings ( that can be found in drinking water networks), or by colonizing the biofilms of the drinking water networks.

Resistance to disinfectants
- to 2 mg/l of chlorine
- to 1mg/l of ozone
- to 160 J/m2 of UV

• stagnating water ( oxbow lake, water tank, condensation tank, elements obstructing a network)
• temperature between 20 and 45°C
• biofilms
• ferric ions, zinc, aluminium, calcium fur, magnesium

The bacteria is transmitted by inhalation of water contaminated by legionellae under the form of  aerosols of a size inferior to 5 µm (shower, steam, air conditioning, nebulisers, humidifier of respiratory devices,…)
Legionella pneumophila can live 2 hours in an aerosol whose relative humidity is of 65%.

Transmission mode :
- Aerial way ( contaminated aerosol)
- Showers
- Taps
- Jacuzzi baths
- Cooling towers
- Air conditioning

Risks
The legionellae can appear under two distinct clinical forms :
1.The “Legionnaires’ disease”: pneumopathy, respiratory distress, renal insufficiency
2.The Pontiac fever:  benign pseudo flu-like syndrome that has a spontaneous cure.
The nosocomial infection is accused in 1 to 10 % of the cases of nosocomial pneumopathies.

Symptoms

The incubation period ( time elapsed between the contact with the microbe and the apparition of the first signs ) of the pneumopathy is 2 to 12 days. The frequency of the legionelloses is higher during the summer because of the water temperature and the frequency of use of the cooling systems.

Both the legionnaires’ disease and the Pontiac fever lead to a pneumopathy that usually starts with :

• A feeling of ill-being
• Headaches
• Muscles pains
• An alteration of the general state
• Shivers
• Fever ( temperature over 40°C for more that half of the patients )
• A cough, dry or not ( that is to say producing an expectoration ) rather frequent
• An hemoptysy ( bloody spittles in feeble quantity )
• A thoracic pain
• A dyspnea ( difficulty to breathe ) that can mislead to a pulmonary embolism diagnostic
• A diarrhoea
• Nausea
• Vomit
• Abdominal pains
• Confusion
• Disorientation
• Lethargy
• Hallucinations
• Depression
• Delirium
• Obsession
• A coma.