eMedicine Specialties > Emergency Medicine > Infectious Diseases

Legionnaires Disease

Author: Frank C Smeeks lll, MD, Chief Medical Officer, Frye Regional Medical Center
Contributor Information and Disclosures

Updated: Jun 1, 2009

Introduction

Background

An outbreak of serious pulmonary infections among people attending a convention of the American Legion in Philadelphia during the US Bicentennial celebration in July 1976 prompted the description of Legionnaires disease and its causative organism, Legionella pneumophila.

A nonpneumonic variant caused by the same species is called Pontiac fever, named for an outbreak of the described disease in Pontiac, Michigan, in 1968.

Pathophysiology

Legionella species are poorly staining, obligate, aerobic, gram-negative bacilli. Serogroup 1 is most frequently identified in clinical disease, but 18 serogroups of L pneumophila are presently known. Other than L pneumophila, 34 species of Legionella have been identified, mostly from immunocompromised patients with pneumonia.

Although pneumonia is the most common presenting problem, other pulmonary manifestations are frequent. The constitutional, cardiac, gastrointestinal, neurologic, renal, musculoskeletal, hepatic, and hematologic abnormalities variably seen with this disease are elaborated in Clinical.

Frequency

United States

Since the initial identification of 235 cases in 1976¹ , Legionnaires disease has become recognized as the most common cause of atypical pneumonia in hospitalized patients. It is the second most common cause of community-acquired bacterial pneumonia. Legionnaires disease is reportable in the United States. The Centers for Disease Control and Prevention (CDC) received reports of 1241 cases in 1995, indicating an incidence of 0.48 cases per 100,000 people.¹ This represents passive disease surveillance. More active surveillance methods estimate that upwards of 20,000 cases occur annually in the United States. Prevalence reports of Legionella have increased with time likely due to the availability of more effective testing modalities. However, it is also possible that Legionella infections are increasing in frequency for environmental, population, or behavioral reasons. 

International

Outbreaks have been recognized throughout North America, Africa, Australia, Europe, and South America.

Mortality/Morbidity

• Legionnaires disease has a 25% mortality rate. However, this figure should be interpreted cautiously because of possible underreporting of comorbid disease.
• Legionnaires disease is frequently associated with gastrointestinal symptoms, including nausea, vomiting, diarrhea, and abdominal pain.
• Neurologic symptoms are also common, including lethargy, altered mental status, and nonfocal neurologic examination findings.
• Hyponatremia is common in Legionnaires disease.
• Rhabdomyolysis and renal failure may be seen in this disease.

Sex

Men are affected more frequently than women.

Age

• The weighted mean age for patients with Legionnaires disease is 52.7 years, with increasing incidence until age 79.
• The incidence in persons younger than 35 years is less than 0.1 cases per 100,000 people.
• Older patients have higher mortality rates.

Clinical

History

• The classical presentation begins with an incubation period of 2-10 days.
• Patients often experience a prodrome of 1-2 days of mild headache and myalgias, followed by high fever, chills, and multiple rigors.
• Cough is present in 90% of cases; cough usually is nonproductive at first but may become productive as the disease progresses.
• Other pulmonary manifestations include dyspnea, pleuritic chest pain, and hemoptysis, which may be present in as many as one third of cases.
• Gastrointestinal symptoms include nausea, vomiting, diarrhea, and anorexia.
• Neurologic symptoms include headache, lethargy, altered mental status, and rarely, focal symptoms.
• Musculoskeletal symptoms include arthralgias and myalgias.
• Nonpulmonary symptoms are prominent early in the disease.

Physical

• The vital signs may reveal high fever and tachypnea. Relative bradycardia may occur in up to 66% of patients.
• Absence of inflammation of the upper respiratory tract is common and is a clinically useful indicator.
• Chest auscultation findings may be normal or may reveal rales, rhonchi, or signs of consolidation.
• Pericarditis and endocarditis may be present.
• Hepatomegaly may be seen in rare cases.
• The neurologic examination findings or the patient's mental status may be abnormal.
• The patient may have blood-streaked sputum.
• Mild, generalized abdominal pain and bloating may be present.
• The rest of the physical examination may be unremarkable, but signs and symptoms of risk factors for the disease should be sought.

Causes

• Investigations of outbreaks have documented aerosol transmission from contaminated water sources, including the following (Note: No person-to-person spread of Legionella is documented.):
  • Cooling systems
  • Showers
  • Decorative fountains
  • Humidifiers
  • Respiratory therapy equipment
  • Whirlpool spas
• Risk factors for Legionnaires disease include the following:
  • Smoking
  • Diabetes
  • Cancer, particularly hematological or pulmonary malignancy
  • AIDS
  • End-stage renal disease
  • Chronic cardiopulmonary disease
  • Advanced age
  • Alcohol abuse
  • Surgery

• Search for CME/CE on This Topic »

• Legionnaires Disease (Infectious Diseases)
• Legionella Infection (Pediatrics: General Medicine)
• Pneumonia, Atypical Bacterial (Radiology)
• Pneumonia, Community-Acquired (Infectious Diseases)

• Severe Legionnaires Disease Complicated by Multi-organ Dysfunction in a Previously Healthy Patient: A Case Report
• Nosocomial Legionellosis: Prevention and Management