Clinical Presentation of Legionella Infection
Legionella infection presents as pneumonia with fever, cough, and dyspnea, but is distinguished by characteristic extrapulmonary features including gastrointestinal symptoms (particularly diarrhea), neurological manifestations (especially confusion), hyponatremia, and elevated liver enzymes. 1
Respiratory Manifestations
- Pneumonia is the hallmark presentation, with cough, dyspnea, and sputum production, though these respiratory symptoms alone cannot distinguish Legionella from other pneumonias. 1
- Physical examination may reveal rales and altered breath sounds, though these findings lack sensitivity and specificity. 1
- Chest radiography typically shows infiltrates, but radiographic patterns are not diagnostic. 2
Fever Pattern
- High-grade fever is characteristic, typically persistent and often reaching 40°C (104°F). 1, 3
- Fever may be accompanied by chills and rigors. 2
Distinguishing Extrapulmonary Features
The following features should raise clinical suspicion for Legionella specifically:
Gastrointestinal Symptoms
- Diarrhea is a key distinguishing feature that points toward Legionella as the causative pathogen. 3
- Abdominal pain may occur and can occasionally dominate the clinical picture, potentially mimicking acute cholecystitis. 4
Neurological Manifestations
- Confusion and altered mental status are common and clinically important features. 1, 3
- Encephalopathy may develop in severe cases. 1
Laboratory Abnormalities
- Hyponatremia (low sodium) is a suggestive laboratory finding that should prompt consideration of Legionella. 1, 3
- Elevated lactate dehydrogenase levels may be present. 1
- Hepatic dysfunction with elevated liver enzymes can occur, occasionally presenting with an atypical 2:1 AST:ALT ratio pattern. 5, 3
Clinical Pitfalls
A critical pitfall is that nonrespiratory symptoms can predominate, leading to misdiagnosis. 3 Cases have been reported where patients initially presented with primarily gastrointestinal or hepatic symptoms, delaying recognition of pneumonia. 4, 5
The absence of typical environmental exposure does not exclude the diagnosis, as cases occur without clear history of exposure to water systems, hot tubs, or cooling towers. 2
Severity Indicators
- Mortality ranges from 5-25% in immunocompetent patients but increases to 40% in ICU patients, immunocompromised individuals, or those with nosocomial infection. 1
- Severe cases may progress to acute respiratory distress syndrome requiring mechanical ventilation. 2
- Multiorgan failure can develop in immunosuppressed patients or severe presentations. 5
High-Risk Populations to Consider
Maintain heightened suspicion in patients with: