Microbiological investigations into an outbreak of Pontiac fever due to Legionella micdadei associated with use of a whirlpool.

In the investigation of a large outbreak of non-pneumonic legionellosis at a leisure complex in Lochgoilhead, Scotland all direct cultures of environmental samples were initially negative for legionellae. Legionellae readily infect appropriate protozoa under suitable conditions, and following immunofluorescence to select specimens for special study, Legionella micdadei was isolated from whirlpool water via co-cultivation with Acanthamoeba polyphaga. L micdadei was also isolated, along with host amoebae, from the whirlpool filter. The use of amoebae in the isolation of legionellae from environmental (and other) sources can be of great value, especially if specimens shown by indirect immunofluorescence to contain legionellae fail to yield legionellae on routine culture.