Legionellacea are gram-negative aerobic bacilli. They are difficult to visualize on Gram's stain.
Water is the primary reservoir of the organism.
Isolation can be difficult as Legionella species do not grow on standard bacteriologic media. The incidence of nosocomial disease likewise varies depending on the techniques used to make the diagnosis and on the patient population studied. While these finding are seen in some cases, it is now widely recognized that Legionnaires' disease may present in a variety of ways. Radiographs are likewise non-specific although the majority of infiltrates are alveolar and not interstitial. Laboratory There are several methods for diagnosing Legionella in addition to culture and these are summarized in the table below.