Legionellosis Outbreak Data Collection Toolbox
Updated: November 2019
WHO surveillance case definitions
• Combined microbiological and epidemiological case definitions are used for surveillance of
legionellosis. Depending on the diagnostic method used and the result, cases are classified
microbiologically as either confirmed or presumptive.
• Based on the patient’s clinical history, cases are classified as one of the following:
o Legionnaires’ disease (relevant pneumonic illness and microbiological evidence of
infection).
o Pontiac fever or similar illness (relevant non-pneumonic illness and microbiological
evidence of infection).
o Asymptomatic legionellae infection (no illness compatible with microbiological result).
o Legionella infection (microbiological evidence of infection but symptoms not known).
