Legionellosis natural history, complications and prognosis

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

Overview

The fatality rate of Legionnaires' disease has ranged from 5 to 30% during various outbreaks. It should be noted that some people can be infected with the Legionella bacterium and have only mild symptoms or no illness at all.

Natural History

Legionnaires' Disease

• The majority of patients do not develop any symptoms (low attack rate). Patients who demonstrate clinical manifestations (approximately 5% to 10%) usually have other co-morbidities (see Risk Factors.
• Infected individuals usually start to develop symptoms 5-7 following transmission (range: 2 days to 19 days).
• Patients report worsening of symptoms of pneumonia (fever, cough, chest pain, dyspnea) at 4 to 6 days following onset of symptoms.
• The majority of patients report resolution 10 days after symptom onset.
• Approximately 1% to 20% of individuals progress to develop Legionnaires'related complications and death.

Pontiac Fever

• Unlike Legionnaires's disease, the attack rate of Pontiac fever is high, and as many as 90% to 95% of exposed individuals will develop symptoms.
• Pontiac fever is characterized by milder symptoms with a shortt illness duration (typically 1-2 days).
• Symptoms of Pontiac fever typically last for a total of 2 to 5 days.
• Development of Pontiac fever-related complications is very rare.

Complications

Complications may develop among patients who develop Legionnaires' disease. Complications may include:

• Empyema
• Emphysema
• Lung failure
• Acute kidney injury
• Peripheral neuropathy
• Severe sepsis, septic shock, and multiorgan failure

In contrast, Pontiac fever is not usually associated with any complications.

Prognosis

• Without treatment, Legionnaires' disease is associated with a case-fatality rate of approximately 5% to 20%.
• Individuals with significant co-morbidities (e.g. renal failure, advanced COPD) are at higher risk of legionellosis-related death.
• A substantially higher proportion of fatal cases occur during nosocomial outbreaks.
• Pontiac fever has an excellent prognosis and is almost always a self-limited disease.

References

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