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, septic shock, and multisystem organ failure. The prognosis is generally good for healthy patients, but patients with co-morbidities 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 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.[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
- 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.