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Legionnaires' disease
OVERVIEW: Legionnaires' disease was coined for an epidemic of lower respiratory tract disease occurring in Philadelphia in 1976 in war veterans. The causative bacterium was identified and named Legionella pneumophila and may cause pneumonia or flu-like illness.
System(s) affected: Pulmonary, Gastrointestinal
Genetics: None known
Incidence/Prevalence in USA: 2-4/100,000/year; 1-4% of community acquired pneumonias; up to 20% of nosocomial pneumonias; thought to be under reported
Predominant age: 15 months-84 years, increased after age 50
Predominant sex: Male > Female
SIGNS AND SYMPTOMS: • Range of illness from asymptomatic seroconversion, mild febrile illness, to severe pneumonia
• Incubation 2-10 days
• Fever, chills
• Malaise, weakness, lethargy
• Anorexia
• Myalgia
• Headache
• Watery diarrhea in up to 50%
• Nausea and vomiting in 10-20%
• Dry cough which may become productive
• Pleuritic chest pain in up to 33%
• Relative bradycardia in up to 67% of patients
• Neuropsychiatric symptoms of confusion, disorientation, obtundation, depression, hallucinations, insomnia, seizures in up to 25%
• Blood streaked sputum; gross hemoptysis rare
• Hyponatremia
• Hypophosphatemia
• Elevated serum transaminases
• Hypotension (17%)
• Wound infections with Legionella have been reported
CAUSES: Legionella pneumophila, a weakly gram negative organism widely distributed in soil and water, acquired by inhalation of infected aerosols
RISK FACTORS: • Smoking
• Alcohol abuse
• Immunosuppression/HIV
• Chronic cardiopulmonary disease
• Surgery
• Advanced age
• Renal failure
DIAGNOSIS DIFFERENTIAL DIAGNOSIS: Other bacterial pneumonias, atypical pneumonias with mycoplasma and chlamydia, viral pneumonias
LABORATORY: • Sputum:
• Gram stain many neutrophils, few organisms
• Direct immunofluorescence 33-70% sensitive
• DNA probe 70% sensitive
• Cultures 80% sensitive
• Urine radioimmunoassay (RIA):
• > 70% sensitivity + 100% specificity
• Intended for detection of L. pneumophila serogroup 1 (which accounts for 70-80% of isolates)
• Blood:
• Indirect immunofluorescence 40-60% sensitive in three weeks and 90% sensitive after 6 weeks (acute and convalescent titers/seroconversion)
• Cultures 20% sensitive. Buffered charcoal yeast extract (BCYE) medium required.
• Polymerase chain reaction
• Experimental; not proven to be more sensitive than culture
Drugs that may alter lab results: N/A
Disorders that may alter lab results: Direct immunofluorescence can cross react with Pseudomonas and Bacteroides species, E. coli, Haemophilus
PATHOLOGICAL FINDINGS: Multifocal pneumonia with alveolitis and bronchiolitis, with fibrinous pleuritis, and may have serous or serosanguinous pleural effusion. Abscess formation in up to 20%.
SPECIAL TESTS: Silver and Gimenez stains for lung tissue/specimens
IMAGING: • Chest x-ray
• Not specific for Legionella
• Commonly with lower lobe patchy alveolar infiltrate with consolidation, usually unilateral
• Cavitation or abscess, especially in immunocompromised
• Pleural effusion in up to 50%
• May take from 1-4 months for the x-ray to return to normal. Progression of infiltrate may be seen despite antibiotic therapy.
DIAGNOSTIC PROCEDURES: Transtracheal aspiration or bronchoscopy for sputum/lung samples
TREATMENT APPROPRIATE HEALTH CARE: Severity of illness and support available in the outpatient setting will dictate the appropriate site for care
GENERAL MEASURES: • Supportive care
• Maintaining oxygenation, hydration, and electrolyte balance while providing antibiotic therapy
SURGICAL MEASURES: N/A
ACTIVITY: As tolerated
DIET: As tolerated
PATIENT EDUCATION: Can educate patients regarding prevention/avoidance measures, lowering their risk status, and if infected already, about the expected course of the disease
MEDICATIONS DRUG(S) OF CHOICE: • Azithromycin 500 mg po qd
• Clarithromycin 500 mg po bid
• Levofloxacin 500 mg po or IV every 24 hours
• Ciprofloxacin IV 400 mg every 8 hours or po 750 mg every 12 hours
• Addition of rifampin 600 mg q 12 hours po or IV should be provided along with above in very ill patients
Contraindications: Hypersensitivity reactions
Precautions: Liver disease
Significant possible interactions:
• Erythromycin can increase theophylline, carbamazepine, and digoxin levels and can increase activity of oral anticoagulants
• Rifampin may decrease the effectiveness of oral anticoagulants, steroids, digoxin, quinidine, oral contraceptives and hypoglycemic agents
ALTERNATIVE DRUGS: • Erythromycin 30-60 mg/kg/day po or IV divided into four doses for 10-21 days
• Tetracyclines may be used along with rifampin
• Doxycycline IV 200 mg every 12 hours x 2 doses, then 100 mg bid or po 200 mg x 1 dose, then 100 mg bid
• Minocycline 100 mg IV or po every 12 hours
• Trimethoprim-sulfamethoxazole IV or po 5 mg/kg TMP every 8 hours
FOLLOW UP PATIENT MONITORING: • Respiratory status, hydration and electrolyte status should be monitored closely
• Chest x-ray not useful to monitor clinical response
PREVENTION/AVOIDANCE: Heating water to 60-70 degrees centigrade may help prevent water contamination. UV light or copper-silver ionization are bactericidal.
POSSIBLE COMPLICATIONS: • Dehydration
• Hyponatremia
• Respiratory insufficiency requiring ventilator support
• Endocarditis
• Disseminated intravascular coagulation
• Renal failure
• Multiple organ dysfunction syndrome (MODS)
• Coma
• Death in 10% of treated non-immunocompromised patients, and in up to 80% of untreated immunocompromised patients
• Bacteremia or abscess formation in immunocompromised
EXPECTED COURSE AND PROGNOSIS: • Recovery is variable, some patients experience rapid improvement with defervescence in 3-5 days and recovery in 6-10 days, while others may have a much more protracted course despite treatment
• Mortality rate can approach 50% with nosocomial infections
MISCELLANEOUS ASSOCIATED CONDITIONS: Pontiac fever - self limited flu-like illness with pneumonia
AGE-RELATED FACTORS:
Pediatric: Less common
Geriatric: Increased incidence in those over age 50
Others: N/A
PREGNANCY: N/A
SYNONYMS: • Legionella pneumonia
• Legionellosis
ICD-9-CM: 482.83 Pneumonia due to other gram negative bacteria
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