Legionella 101

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Legionella 101

• Danae Bixler, MD, MPH

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Legionella Basics

• Does the patient meet the case definition?
• Clinical criteria
• Legionnaires, OR
• Pontiac Fever.
• Laboratory criteria
• Positive culture, OR
• Positive DFA, OR
• 4-fold rise in antibody titer, OR
• Positive urinary antigen.

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Legionellosis

• Pneumonia (atypical)
• Rapidly progressing infiltrates involving one or
  more lobes
• Indistinguishable clinically from pneumonia
  due to other causes
• Caused by Legionella species bacteria
• At least 43 species
• 65 serotypes

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Clinical Features of Legionnaires
DiseaseEpidemiologic Reviews, 1991 13329 and
Chest, 1994 1051817

• Headache
• Fever
• Myalgia
• Cough
• Dyspnea gt respiratory failure
• Pleuritic chest pain
• Extrapulmonary manifestations
• Diarrhea / abdominal symptoms
• Delirium / CNS

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Legionnaires Disease vs. Pontiac
FeverEpidemiologic Reviews, 1991 13329 and
Chest, 1994 1051817.

• Legionnaires
• Incubation period 2-10 days
• Atypical pneumonia
• Older individuals chronic underlying disease
• Mortality 5-30
• Low attack rate (5)

• Pontiac Fever
• Incubation period mean 36 hours
• Influenza-like illness
• Persons without chronic medical conditions
• Self-limited
• High attack rate (95)

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Legionellosis (Legionella pneumophila) 1996 Case
Definition

• Clinical description
• Legionellosis is associated with two clinically
  and epidemiologically distinct illnesses
  Legionnaires disease, which is characterized by
  fever, myalgia, cough, pneumonia, and Pontiac
  fever, a milder illness without pneumonia.
• Laboratory criteria for diagnosis
• Case classification
• Confirmed a clinically compatible case that is
  laboratory confirmed
• Comment
• The previously used category of "probable case,"
  which was based on a single IFA titer, lacks
  specificity for surveillance and is no longer
  used.

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Diagnosis of LegionellosisAm J Med, 2001
11041-48 and Cleve Clin J Med, 2001 68318-322.

• Sputum culture
• Selective media
• Sputum of patients with suspected Legionella
  should be cultured regardless of quality
• Sensitivity
• 10 compared to serology
• 61 compared to DFA
• Better if transtracheal / endotracheal
• Slow - growing

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Diagnosis of LegionellosisAm J Med, 2001
11041-48 and Cleve Clin J Med, 2001 68318-322.

• Direct Fluorescent Antibody (DFA) stain of sputum
• Rapid test that requires large numbers of
  bacteria to be visualized
• Technically demanding
• Useless with non-expectorating patients unless
  bronchoscopy or tracheal aspiration are performed
• Sensitivity about 50 (vs. all diagnostic
  modalities) dependent on serotypes included in
  the panel
• Specificity close to 100

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Diagnosis of LegionellosisAm J Med, 2001
11041-48 and Cleve Clin J Med, 2001 68318-322.

• Urinary antigen assay
• Inexpensive and rapid
• Sensitivity 53 70
• May not turn positive until after 5 days of
  illness
• May remain positive for up to 6 weeks in some
  patients
• Only detects L pneumophila serogroup 1 however
  serogroup 1 accounts for most disease

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Diagnosis of LegionellosisAm J Med, 2001
11041-48 and Cleve Clin J Med, 2001 68318-322.

• Serologic Testing
• Requires acute and convalescent samples
• May require 8 10 weeks or more for
  seroconversion to occur
• High prevalence of antibodies in the general
  population limits utility of a single titer.
• Sensitivity 75 80

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Diagnosis of LegionellosisAm J Med, 2001
11041-48.

• PCR
• Fast
• Sensitivity about 70
• Potentially may be used for sputum, urine,
  environmental samples
• Research status
• Has the potential to affect clinical management

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Diagnosis - Summary

• No one test offers
• Rapid results
• Sensitivity
• Some physicians may, . . . treat first and not
  bother to ask questions later. Am J
  Med, 2001 11041-18.

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Legionellosis (Legionella pneumophila) 1996 Case
Definition

• Clinical description
• Laboratory criteria for diagnosis
• Isolation of Legionella from respiratory
  secretions, lung tissue, pleural fluid, or other
  normally sterile fluids, or
• Demonstration of a fourfold or greater rise in
  the reciprocal immunofluorescence antibody (IFA)
  titer to greater than or equal to 128 against
  Legionella pneumophila serogroup 1 between paired
  acute- and convalescent-phase serum specimens, or
  
• Detection of L. pneumophila serogroup 1 in
  respiratory secretions, lung tissue, or pleural
  fluid by direct fluorescent antibody testing, or
• Demonstration of L. pneumophila serogroup 1
  antigens in urine by radioimmunoassay or
  enzyme-linked immunosorbent assay
• Case classification

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Case 1
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Case 1
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Case 2
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Case 2
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Case 3
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Case 3
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Conclusions

• Case ascertainment
• Must meet one clinical criterion AND one
  laboratory criterion
• WVEDSS is your friend
• For sporadic cases
• Do investigate
• Travel
• Hospital stay
• Dont test the water