The Organism and Epidemiology

• More than 30 species of Legionella have been identified but 90% human disease is caused by Legionella pneumophilia. There are 14 serogroups of Legionella pneumophilia though more than 80% of reported cases of Legionellosis are caused by serogroup 1 (1,2).
• Water is the primary reservoir of the organism. Warm temperatures (45-50 oC), nutrient biofilms and commensal bacteria, all of which are found in large water distribution systems, promote growth of Legionella (9).
• Legionella is one of the top 3 or 4 causes of community acquired pneumonia accounting for 2-15% of pneumonias in hospitalized patients (6). Cases are likely underreported owing to the difficulties with recovering the organism (7).

Laboratory

• There are several methods for diagnosing Legionella.It should be noted, however, that culture remains the gold standard and is important in that it allows speciation and typing of the isolate.
• Urinary antigen testing is becoming increasingly popular but can ONLY detect infections due to serogroup 1.
• PCR detection shows promise but is not yet available clinically.
• Report any cases of Legionella pneumonia to HEIC IMMEDIATELY at 3-3855.

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Prevention

• Chlorine-Dioxide disinfection systems are being installed in all in-patient care buildings
• Water must be run DAILY in all patient care rooms to ensure flushing of chlorine dioxide throughout the system. Both hot and cold water of the faucets and showerheads should be run for at least 5 minutes each.

Patient Care

• Sterile water is used for rinsing nebulizers & other semi-critical respirator-care equipment
• Physicians are advised to routinely send sputum and BAL specimens and urinary antigens for Legionella in high-risk patients with pneumonia
• All bronchoscopy specimens, tracheal aspirates and pleural fluid from patients suspected of having nosocomial pneumonia should be submitted for Legionella culture
• Water cultures are done semi-annually in buildings that house high-risk patients

Companion Documents:

• Centers for Disease Control (CDC), Prevention of Legionnaires’ Disease in Health Care Facilities, 1994.
• State of Maryland, Report of the Maryland Scientific Working Group to Study Legionella in Water Systems in Healthcare Institutions, June 14, 2000.

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