Legionellosis pathophysiology

Pathophysiology
Legionella pneumophila and other Legionella species. At least 46 species and 70 serogroups have been identified. L.pneumophila, an ubiquitous aquatic organism that thrives in warm environments (32°- 45°C) causes over 90% of LD in the United States. The disease has two distinct forms:


 * Legionnaires' disease, the more severe form of infection which includes pneumonia, and
 * Pontiac fever, a milder illness.
 * Pontiac fever and Legionnaires’ disease may also be called “Legionellosis” (LEE-juh-nuh-low-sis) separately or together.

How do people get Legionnaires’ disease?
People get Legionnaires' disease when they breathe in a mist or vapor (small droplets of water in the air) that has been contaminated with the bacteria. One example might be from breathing in the steam from a whirlpool spa that has not been properly cleaned and disinfected.

The bacteria are NOT spread from one person to another person.

Outbreaks are when two or more people become ill in the same place at about the same time, such as patients in hospitals. Hospital buildings have complex water systems, and many people in hospitals already have illnesses that increase their risk for Legionella infection.

Other outbreaks have been linked to aerosol sources in the community, or with cruise ships and hotels, with the most likely sources being whirlpool spas, cooling towers (air-conditioning units from large buildings), and water used for drinking and bathing.

Infections
Intestinal Infections: These may only occur as part of respiratory infections, and where gastrointestinal symptoms have on occasion been described.

Extraintestinal Infections: L. pneumophila is specifically considered as a pathogen of the respiratory tract, where it is a cause of atypical pneumonia, also known as Legionnaires' disease. Other infections have also been reported, including haemodialysis fistulae, pericarditis and wound and skin infections. Bacteraemia is often associated with Legionnaires' disease.

Infections of Protozoa: Protozoa such as Harmanella vermiformis and related protozoa have been shown to be able to support the growth of L. pneumophila in tap water. Also Acanthamoeba, Naegleria and Tetrahymena can be infected by L. pneumophila. This pathway may be how these organisms survive in the environment.