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Legionella
Aerobic gram negative bacilli. Motile. Ubiquitous in aquatic environments. There are 22 Legionella species & 33 serotypes identifiable by a slide agglutination test.
Epidemiology:
1) natural habitat is water
2) epidemics have occurred
a) contaminaed air-conditioning cooling towers
b) construction or excavation in contaminated soil
c) contaminated hospital showers
3) most cases occur in summer & early autumn
4) 7% of community-acquired pneumonia
5) 25% of atypical pneumonias
6) 10% of nosocomial infections
Pathology:
1) aerosolized & inhaled bacteria
2) human to human transmission does not occur
3) 50% of adults have serologic evidence of prior infection
4) risk factors
a) debilitated & immunocompromised patients
b) COPD
c) tobaccoism (smoking)
d) cancer
e) diabetes mellitus
f) chronic heart disease
g) chronic renal failure
Clinical manifestations: (see Legionella pneumophila)
Laboratory:
1) Legionella antigen in tissue/body fluid
- direct fluorescent antibody (DFA): 50% sensitivity
- Legionella antigen in urine
- sensitivity for Legionella pneumophila 60-80%; specificity > 99%
2) Legionella serology
a) indirect fluorescent antibody (IFA): 50% sensitivity, identifies only serogroup 1
b) 4-fold rise in titer over 3 weeks to at least 1:128
c) single titer of 1:256
d) false positive titers may be seen with
1] plague
2] tularemia
3] leptospirosis
4] adenovirus
3) Legionella identified in isolate
- Dieterle's stain
4) Legionella identified by culture:
- growth on buffered charcoal yeast agar (low yield)
- can detect all forms of Legionella
5) Legionella DNA 70% sensitive, 99% specific [4]
6) Legionella rRNA
Management:
1) antimicrobial therapy
a) erythromycin
- 500 mg PO every 6 hours for mild cases
- 1 g IV every 6 hours for severe cases
- continue therapy for 21 days
b) Rifampin 600 mg PO QD may be synergistic
c) alternative antibiotics
- doxycycline
- Bactrim
- clarithromycin
- quinolone
2) Legionella endocarditis
a) valve replacement
b) 3-12 months of antibiotic therapy
Related
Legionella antigen in urine
Legionella DNA
Legionella identified by culture
legionellosis
Specific
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
General
gram-negative aerobic bacteria
Properties
KINGDOM: monera
DIVISION: SCHIZOMYCETES
References
- Harrison's Principles of Internal Medicine, 13th ed.
Companion Handbook, Isselbacher et al (eds), McGraw-Hill
Inc. NY, 1995, pg 228-29
- Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed)
Lippincott-Raven, Philadelphia, 1998, pg 797
- Medical Knowledge Self Assessment Program (MKSAP) 11, 19American
College of Physicians, Philadelphia 1998, 2021
- Harrison's Principles of Internal Medicine, 13th ed.
Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 657