Legionella

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Contents 1 More Specific Terms 2 Introduction 3 Epidemiology 4 Pathology 5 Clinical-manifestations 6 Laboratory 7 Management 8 More General Terms 9 Additional Terms 10 References

More Specific Terms

• Legionella anisa
• Legionella birminghamensis
• Legionella bozemanii
• Legionella cherrii
• Legionella cincinnatiensis
• Legionella dumoffii
• Legionella feeleii
• Legionella gormanii
• Legionella hackeliae
• Legionella jordanis
• Legionella lansingensis
• Legionella longbeachae
• Legionella maceachernii
• Legionella micdadei
• Legionella oakridgensis
• Legionella pneumophila
• Legionella sainthelensi
• Legionella tucsonensis
• Legionella wadsworthii

Introduction

• Aerobic gram negative bacilli. Motile. Ubiquitous in aquatic environments. There are 22 Legionella species & 33 serotypes identifiable by a slide agglutination test.

Epidemiology

• natural habitat is water
• epidemics have occurred

• contaminaed air- conditioning cooling towers
• construction or excavation in contaminated soil
• contaminated hospital showers

• most cases occur in summer & early autumn
• 7% of community-acquired pneumonia
• 25% of atypical pneumonias
• 10% of nosocomial infections

Pathology

• aerosolized & inhaled bacteria
• human to human transmission does not occur
• 50% of adults have serologic evidence of prior infection
• risk factors

• debilitated & immunocompromised patients
• COPD
• tobaccoism ( smoking)
• cancer
• diabetes mellitus
• chronic heart disease
• chronic renal failure

Clinical-manifestations

• (see Legionella pneumophila)

Laboratory

• urine Legionella antigen testing

• sensitivity for Legionella pneumophila 60-80%; specificity > 99%

• culture:

• growth on buffered charcoal yeast agar (low yield)
• can detect all forms of Legionella

• direct fluorescent antibody ( DFA): 50% sensitivity
• Dieterle's stain
• serology

• indirect fluorescent antibody (IFA): 50% sensitivity, identifies only serogroup 1
• 4-fold rise in titer over 3 weeks to at least 1:128
• single titer of 1:256
• false positive titers may be seen with

• plague
• tularemia
• leptospirosis
• adenovirus

• DNA probe 70% sensitive, 99% specific [4]

Management

• ( antimicrobial therapy)

• erythromycin

• 500 mg PO every 6 hours for mild cases
• 1 g IV every 6 hours for severe cases
• continue therapy for 21 days

• Rifampin 600 mg PO QD may be synergistic
• alternative antibiotics

• doxycycline
• Bactrim
• clarithromycin
• quinolone

• Legionella endocarditis

• valve replacement
• 3-12 months of antibiotic therapy

More General Terms

• gram-negative aerobic bacteria

Additional Terms

• Legionella antigen in urine
• Legionella culture
• legionellosis
• PCR/southern blot/in-situ hybridization for Legionella

References

1. Harrison's Principles of Internal Medicine, 13th ed. Companion Handbook, Isselbacher et al (eds), McGraw-Hill Inc. NY, 1995, pg 228-29
2. Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 797
3. Medical Knowledge Self Assessment Program (MKSAP) 11, American College of Physicians, Philadelphia 1998
4. Harrison's Principles of Internal Medicine, 13th ed. Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 657

Legionella