What is Legionella?
Legionella is a genus of potentially pathogenic (Legionnaires’ disease-causing) bacteria that live in environmental water ecosystems, inside of free-living amoebae and within the microscopically diverse water/surface biofilms. In addition to lakes and streams, these Legionella-containing biofilms commonly the genus Legionella contains at least 50 identified species and more than 70 different serogroups. The species L. pneumophila is responsible for 90% of the cases of Legionnaires’ disease, and the serogroup L. pneumophila serogroup 1 is the cause of virtually all community-acquired outbreaks of Legionnaires’ disease.
What is Legionnaires’ disease?
Legionnaires’ disease is an acute pneumonia caused by inhalation of an aerosol of environmental water containing an infectious dose of L. pneumophila, or less commonly, one of the other Legionella species. The disease can be rapidly fatal if not treated aggressively with the appropriate antibiotics, especially in hospital-acquired disease in immunocompromised patients with underlying health conditions.
The first documented outbreak of Legionnaires’ disease was at the 1976 convention of the American Legion, where 221 of the attendees contracted the disease and 34 died. The name of the disease and the genus name came from this first association with the American Legion. Since then, there has been a steady rise in the recognition of outbreaks of Legionnaires’ disease, including a large outbreak in the South Bronx of New York City during three weeks of the summer of 2015, where there were 133 cases and 16 deaths from exposure to a single contaminated cooling tower on top of a hotel building. Hospital-acquired disease is more common and is linked to exposure to the contaminated hot water loops of the premise plumbing in hospitals and nursing homes. Outbreaks from exposure to the hot water loops in hotels has also been documented.