Legionellosis classification

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

Overview

Legionellosis (Legionella spp. infection) can be classified into three types based upon the affected organ systems and the clinical presentation: pulmonary infection (Legionnaires' disease), extrapulmonary infection, and Pontiac fever.

Classification

Legionellosis (Legionella spp. infection) can 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

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%