Legionellosis natural history, complications and prognosis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Yazan Daaboul, M.D.; Serge Korjian M.D.
Overview
In Legionnaires' disease, the majority of exposed patients do not develop any symptoms. Patients who develop clinical manifestations usually report pneumonia-like symptoms that worsen at 4 to 6 days following onset of symptoms and eventually resolve by day 5 to 10 of symptom-onset. Approximately 1% to 35% of individuals progress to develop Legionnaires'-related complications and death. Complications of Legionnaires' disease include empyema, lung failure, acute kidney injury, endocarditis, neurological disease, septic shock, and multi-organ failure. The prognosis is generally good for healthy patients, but patients with co-morbidities are at higher risk of developing complications and death. In contrast, Pontiac fever has a high attack rate but is associated with mild flu-like symptoms that resolve within 1 to 2 days and is almost always self-limited without any complications.
Natural History
Legionnaires' Disease
- The majority of exposed 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).[1]
- Patients report worsening of symptoms of pneumonia (fever, cough, chest pain, dyspnea) at 4 to 6 days following onset of symptoms.[1]
- The majority of patients report resolution 10 days after symptom onset.
- Approximately 1% to 35% 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.[1]
- Pontiac fever is characterized by mild flu-like symptoms with a short illness duration (typically 1-2 days).
- Symptoms of Pontiac fever typically last for a total of 2 to 5 days.[1]
- Development of Pontiac fever-related complications is very rare.
Complications
Complications may develop among patients who develop Legionnaires' disease. Complications may include:[1]
- Empyema
- Emphysema
- Lung failure
- Acute kidney injury
- Endocarditis
- 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 that may be as high as 35%.[1]
- 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.