Legionellosis classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Legionellosis may be classified into three types based upon the affected organ systems and the clinical presentation: pulmonary infection (Legionnaires' disease), extrapulmonary infection, and Pontiac fever. Legionellosis may also be classified based on the infectious species responsible for the disease.

Clinical Classification

Legionellosis may be classified into three types based upon affected organ systems and clinical presentation:

Pulmonary Infection (Legionnaires' Disease)

• Legionnaires' disease may further be classified into:

• Healthcare associated Legionnaires' disease
• Pittsburgh pneumonia (caused by L. micdadei)

Extrapulmonary Legionella Infection

• The following organ systems may be involved:

• Cutaneous involvement legionellosis
• Legionella encephalopathy
• Disseminated legionella infection

Pontiac Fever

• A mild flu-like infectious disease without pneumonia. It is often distinguished from Legionnaires' disease by clinical features (see table below).

Characteristic	Legionnaires' disease	Pontiac fever
Clinical features	Pneumonia, cough, fever	Flu-like illness (fever, chills, malaise) without pneumonia
Radiographic pneumonia	Yes	No
Incubation period	2-14 days after exposure	24-72 hours after exposure
Etiologic agent	Legionella species	Legionella species
Attack rate[1]	< 5%	> 90%
Isolation of organism	Possible	Never
Outcome	Hospitalization common Case-fatality rate: 5-30%	Hospitalization uncommon Case-fatality rate: 0%

Microbiological Classification

Legionellosis may also be classified based on the infectious species responsible for the disease. Species of Legionella include:

• L. pneumophila
• L. feeleii
• L. sainthelensi