Legionnaires' disease outbreak investigation toolbox

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Definition of Legionellosis

Legionellosis is the collective term for all cases of Legionella infection and includes Legionnaires' disease and Pontiac fever.

Table 1: Infection definitions



Legionnaires' disease

pneumonic form of the disease caused by L. pneumophila or other Legionella species

Pontiac fever[1]

acute, self-limiting influenza-like illness without pneumonia. When observed the illness has a high attack rate, though given the non-specific nature of symptoms un-linked cases are rarely seen

Non-pneumonic cases of legionellosis

occasionally, L. pneumophila urinary antigen positive cases are detected which do not fit into the definition of Pontiac fever and have no evidence of any pneumonia

[1] Another species of Legionella , L. micdadei , is responsible for a similar form of the illness without pneumonia called Lochgoilhead fever after an outbreak in Lochgoilhead, Scotland. The incubation period can be up to 9 days. A high percentage of those exposed to this agent tend to be affected. However, there have been no recorded deaths associated with either Pontiac or Lochgoilhead fevers.