Clinical Features
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Legionellosis is bacterial respiratory disease caused by Legionella that can present as either Legionnaires’ disease or Pontiac fever. Legionnaires’ disease is a common cause of severe pneumonia requiring hospitalization, while Pontiac fever generally resolves on its own.
The following table summarizes key clinical differences between Legionnaires’ disease and Pontiac fever.
| Legionnaires’ disease | Pontiac fever | |
|---|---|---|
| Clinical features | Fever, myalgia (body aches), and cough are included in the CSTE case definition. These symptoms are typical but may not always be present in all patients and are considered optional for meeting the CSTE case definition. Additional symptoms may be present, such as shortness of breath, headache, confusion, nausea, or diarrhea. | A milder illness without pneumonia is included in the CSTE case definition, often a flu-like illness (fever, chills, myalgia, malaise). |
| Pneumonia (clinical or radiographic) | Yes | No |
| Pathogenesis | Replication of organism | Possibly an inflammatory response to endotoxin |
| Incubation period | 2 to 10* days after exposure | 24 to 72 hours after exposure |
| Percent of persons who become ill, when exposed to the source of an outbreak | Less than 5% | Greater than 90% |
| Treatment | Antibiotics | Supportive care (self-resolving) |
| Isolation of organism | Possible | Never possible |
| Outcome | Hospitalization common Case-fatality rate: 10%, (25% for healthcare-associated) |
Hospitalization uncommon Case-fatality rate: 0% |
* The incubation period for Legionnaires’ disease is most commonly 2 to 10 days from the time of exposure to symptom onset, with an average of 5 to 6 days but has been reported to be up to 19 days in rare cases. For routine surveillance purposes, exposure histories are collected for the 10 days prior to onset. However, in outbreak settings where it is important to consider a wide range of possible sources, use of a 14-day incubation period is often desirable.
- Page last reviewed: June 1, 2017
- Page last updated: June 1, 2017
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