Legionella

Legionella is a genus of Gram-negative bacteria found mainly in natural and engineered water systems. Some species infect humans and cause Legionnaires’ disease or Pontiac fever.

Pontiac fever: A self-limited, flu-like illness caused by exposure to Legionella bacteria, without pneumonia. It is the milder illness linked to the same bacterial genus.
Legionella pneumophila serogroup 1: A serological subgroup of Legionella pneumophila associated with many cases of Legionnaires’ disease. Many diagnostic tests and surveillance efforts specifically target this subgroup.
1976 Philadelphia Legionnaires’ disease outbreak: An outbreak of severe pneumonia among attendees of an American Legion convention in Philadelphia in 1976. Investigators identified the previously unknown bacterium after this outbreak.
Biofilm: A community of microorganisms attached to a surface and embedded in a self-produced matrix. Biofilms in plumbing can shelter Legionella from environmental stress and disinfection.
Streptococcus pneumoniae: A bacterium that commonly causes community-acquired pneumonia and other infections. It is a frequent pneumonia cause, but does not share Legionella’s characteristic water-aerosol exposure.
Legionella-containing vacuole: A modified compartment inside a host cell where Legionella pneumophila replicates while evading normal destruction. It provides the intracellular niche that allows pathogenic Legionella to multiply.
Urinary antigen test: A diagnostic test that detects Legionella antigens in urine, especially those of L. pneumophila serogroup 1. It enables rapid diagnosis of a major share of Legionella pneumonia cases.
David W. Fraser: An epidemiologist who led investigation of the 1976 Philadelphia outbreak of Legionnaires’ disease. His investigation helped establish the outbreak’s scale and transmission pattern.
Waterborne disease: An illness caused by pathogens transmitted through water or water-associated exposure. Legionella infections belong to this broader class, though inhaled aerosols are the usual route.
Chlamydia pneumoniae: An intracellular bacterium that causes respiratory infections, including pneumonia. Both can cause atypical pneumonia, but their transmission and environmental reservoirs differ.

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