Legionnaires' Disease
Legionellosis is an infection caused by the genus of Gram negative bacteria Legionella, notably Legionella pneumophila At least 50 species and 70 serogroups have been identified. L. pneumophila, a ubiquitous aquatic organism that thrives in warm environments (25 to 45 °C with an optimum around 35 °C) causes over 90% of Legionnaires' disease cases
The disease has two distinct forms:
- Legionnaires' disease is the name for the more severe form of infection which includes pneumonia
- Pontiac fever is a milder respiratory illness without pneumonia caused by the same bacterium.
Legionnaires' disease acquired its name in 1976 when an outbreak of pneumonia occurred among people attending a convention of the American Legion in Philadelphia. On January 18, 1977 scientists identified the causative agent as a previously unknown bacterium, subsequently named Legionella.
An estimated 8,000 to 18,000 people get Legionnaires' disease in the United States each year Some people can be infected with the Legionella bacterium and have mild symptoms or no illness at all.
Outbreaks of Legionnaires' disease receive significant media attention. However, this disease usually occurs as a single, isolated case not associated with any recognized outbreak. When outbreaks do occur, they are usually recognized in the summer and early autumn, but cases may occur at any time of year. The fatality rate of Legionnaires' disease has ranged from 5 to 30% during various outbreaks.