Infection by Legionella pneumophila results mainly in Legionnaire's Disease. However, some strains of the bacteria have been known to manifest a disorder called Pontiac Fever. This is a very mild infection which causes influenza-like symptoms and will go away without treatment. Incidence of Legionellosis or Legionnaire's Disease have increased over the past decade or so because of the use of central air conditioning, especially in office buildings, hotels, and hospitals.
The first symptoms of Legionnaires Disease are noticed anywhere within two to ten days post-infection. On average, however, its usual incubation is about five to six days. It is primarily characterized by a bacterial pneumonia. Initially, however signs such as anorexia, malaise, myalgia, and headache should concern doctors of the possibility of infection by the Legionella bacterium5. Other more specific symptoms of this disease are:
The majority of patients that develop Legionnaire's Disease eventually become delirious. Doctors can also diagnose this disease by looking at X-RAY films. In most cases heavy lung damage is an obvious characteristic, as well as large pockets of fluid in the alveoli. If necessary a laboratory can also analyze pieces of lung tissue. In these tissue samples scientists can look for areas of extensive lysis of phagocytotic cells where the bacteria have accumulated.
The major side-effect of Legionnaire's Disease is is respiratory failure which requires mechanical ventilation. Other complications are acute renal failure, hypotension, and shock.
In hospitalized patients the most recent case fatality rate has been determined to be fifteen percent.
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