Symptoms of Legionnaires' Disease
Legionnaires' disease presents as pneumonia with respiratory symptoms (cough, dyspnea, sputum production) accompanied by high fever, but cannot be reliably distinguished from other pneumonias based on clinical features alone. 1
Core Respiratory Manifestations
- Respiratory distress is universally present in patients requiring hospitalization, with cough, dyspnea, and sputum production as primary symptoms 2
- Fever is a hallmark feature, typically high-grade and persistent 1
- Rales and altered breath sounds may be detected on physical examination, though these findings are neither sensitive nor specific 1
- Severe cases frequently require ventilatory support, with 14 of 17 ICU patients in one series needing mechanical ventilation 2
Characteristic Extrapulmonary Features
While no single finding is pathognomonic, certain extrapulmonary manifestations suggest Legionnaires' disease when present together:
- Hyponatremia (low sodium levels) is a suggestive laboratory finding 1
- Central nervous system manifestations including confusion, altered mental status, or encephalopathy 1
- Elevated lactate dehydrogenase levels (≥700 U/mL) may be present 1
- Gastrointestinal symptoms can occur as part of the systemic illness 3
Severe Disease Indicators
- Profound shock requiring hemodynamic support is commonly encountered in ICU patients 2
- Acute renal failure develops frequently in severe cases 2
- Multiorgan failure can occur, with complications including jaundice, rhabdomyolysis, and polyneuropathy 2
- Mortality rates range from 5-25% in immunocompetent hosts and up to 40% in ICU patients, immunocompromised patients, or those with nosocomial infection 1, 4
Critical Diagnostic Pitfall
Several studies demonstrate that individual cases of Legionnaires' disease cannot be reliably distinguished from other causes of community-acquired pneumonia based on initial clinical findings, laboratory results, or chest radiographs alone. 1 This means that while the constellation of high fever, hyponatremia, CNS manifestations, and elevated LDH may suggest the diagnosis, these features lack sufficient sensitivity and specificity for definitive clinical diagnosis 1
Risk Factor Clues
Suspect Legionnaires' disease particularly when pneumonia occurs with:
- Recent travel with overnight stay outside the home 1
- Exposure to spas, hot tubs, or cooling towers 1
- Recent changes in domestic plumbing 1
- Underlying immunosuppression, including transplant recipients, hematologic malignancy, or end-stage renal disease 1
- Advanced age, smoking, diabetes, or chronic lung disease 1
Temporal Presentation
The clinical features are nonspecific at presentation, requiring high clinical suspicion based on epidemiologic risk factors rather than symptom patterns 2, 3 Laboratory confirmation typically requires days to weeks when relying on serologic testing, emphasizing the need for empiric treatment in suspected cases 2