Legionella pneumophila

Cell Wall: Gram Negative Shape: Coccoid Rod
Metabolism: Obligate Aerobe Life cycle: Facultative Intracellular
  • L. pneumophila survives and replicates in watery environments and infects via inhalation of aerosolized droplets. Outbreaks of disease are due to contamination of the water supply. The organism does not appear to spread from person-to-person.
Clinical Consequences
  • Overview
    • Inhaled organisms are phagocytosed by alveolar macrophages but resist being killed inside the phagosome. They replicate within the phagosome, evading humoral immunity, and lyse the cell, subsequently being phagocytosed by freshly recruited marcophages. Infection is asymptomatic in many individuals but can result in clinical disease with two possible patterns as described below.
  • Pontiac Fever
    • Is a flu-like illness characterized by constitutional symptoms such as myalgia, fever, chills, and fatigue. The syndrome is self-limited and resolves within several days.
  • Legionnaries' Disease
    • Legionnaries' Disease is characterized as an atypical community-acquired pneumonia due to its relatively non-productive cough and unimpressive production of purulent sputum. Constitutional symptoms are common with extremely high fevers. Disease can progress to a serious illness that is fatal in a small minority of individuals.
  • First Choices: Azithromycin
  • Alternative Choices: Bactrim