Legionellosis may be classified into three clinically different diseases, all of which vary in disease presentation, organ system affected, and severity: pulmonary infection (Legionnaires’ disease), extrapulmonary infection, and Pontiac fever, which has causes only mild disease. Legionellosis may also be classified based on the causative species.

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

Legionnaires’ disease may further be classified into:

• Community-acquired Legionnaires’ disease, which is most commonly caused by L. pneumophila ^[1]
• Healthcare associated Legionnaires’ disease which is also most commonly caused by L. pneumophila ^[2]
• Pittsburgh pneumonia which is caused by L. micdadei ^[3]

Legionella can skin infection soft tissue infection, endocarditis, wound infection, joint infection, and graft infection.

• Pontiac fever produces a mild, self-limiting, non-fatal illness without symptoms or radiologic findings of pneumonia. A comparison of Pontiac fever and Legionnaires’ disease is as follows:

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

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