Legionnaire's Disease, referred to medically as legionellosis, is a potentially fatal respiratory illness. 90%
of cases of Legionnaire's Disease are caused by legionella pneumophilia, a particularly common and
resilient species of legionella. Legionellosis can present itself in a mild form as Pontiac Fever, which is
characterized by flulike symptoms such as fever, chills, muscle aches, and headaches. However, if
pneumonia accompanies these flulike symptoms then the illness is considered to be Legionnaire's
Disease, also known as Legion Fever.
People of any age can suffer Legionnaire's Disease. However, the illness most commonly affects the middle aged or the elderly, as well as smokers, those with preexisting lung conditions, or the immunocompromised. During outbreaks, it is reasonable to expect a large variety between people afflicted with the illness, and therefore it is not possible to target a specific demographic with preventative measures.
The CDC states that Legionnaire's Disease has a fatality rate of anywhere between 5% to 30% depending on a number of variables, including the rapidity with which treatment is provided. Generally, Legionnaire's Disease will not be fatal if treatment is administered early to an otherwise healthy individual. However, a legionella infection that is hospital acquired can reach a fatality rate of 50%, which indicates the sheer danger which Legionnaire's Disease can pose.
Legionnaire's Disease can be contracted by breathing air that contains droplets of water contaminated
with legionella bacteria. Often, these droplets of water will trace their origin to a cooling tower, since
pipes cycling in cooling towers are typically the perfect environment for legionella to grow, causing
cooling towers to facilitate the evaporation of contaminated water. Cooling towers then push out this
evaporated water and then the air will contain droplets of water contaminated with legionella.
There is no evidence to suggest Legionnaire's Disease can be spread from person to person. Cases of legionellosis are usually found to have their origin in evaporative cooling systems - if an origin is found at all. Airborne legionella can travel up to six kilometres. In outbreaks, such as the 2005 Toronto outbreak, nearby cooling towers not associated with the outbreak were also found to contain legionella.
To sum up: while Legionnaire's Disease cannot be spread from person to person, legionella can travel very far distances and therefore outbreaks can be spread over a large area of population. When outbreaks occur, they are curbed by prompt and thorough inspection and decontamination of cooling towers and facility mechanical systems.