Clinical Features of Legionnaires' Disease and Pontiac Fever

Key points

  • Legionnaires' disease and Pontiac fever are two illnesses caused by bacteria called Legionella.
  • They present differently in terms of clinical features, symptoms, and complications.
  • The organism can be isolated in Legionnaires' disease cases, but not for Pontiac fever.
A healthcare provider listens to a man's breathing through a stethoscope

Clinical features

Legionnaires' disease

Legionnaires' disease is characterized by illness with pneumonia diagnosed radiographically or clinically.

Evidence of clinically compatible disease can be determined from the medical record in several ways:

  1. Clinical or radiographic diagnosis of pneumonia
  2. Description of clinical symptoms consistent with a pneumonia diagnosis

Pontiac fever

Pontiac fever is a milder, self-limiting illness without pneumoniaA.

Common signs and symptoms

Legionnaires' disease

Clinical symptoms may vary but include acute onset of lower respiratory illness with fever or coughA. Additional symptoms may be present:

  • Chest discomfort
  • Headache
  • Malaise
  • Myalgia
  • Nausea, diarrhea, or abdominal pain
  • Shortness of breath

Pontiac fever

Symptoms include:

  • Chills
  • Fatigue
  • Fever
  • Headaches
  • Malaise
  • Myalgia
  • Nausea or vomiting


Legionnaires' disease

Hospitalization is common. The case-fatality rate is approximately 10%. For healthcare-associated infections, the case-fatality rate averages 25%.

Pontiac fever

Hospitalization is uncommon. The case-fatality rate is extremely low.