Diagnosis of Community Acquired Pneumonia

1
Diagnosis of Community Acquired Pneumonia

• Eva ampachová
• Virology
• Hospital Ceské Budejovice

2
Characteristic symptoms of CAP

• Bacterial
• acute onset, high fever, cough with expectoration
  (purulent), high level of CRP, typical clinical
  findings and X-ray
• Atypical
• slower onset, fever (often without cough),
  expectoration scarce or none, low to moderate CRP
  level, unspecific clinical findings, X-ray
  reveals pneumonia

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Community Acquired Pneumonia (CAP)

• Bacterial
• Pneumococcus, Haemophillus, Moraxella, Gram
  negative rods, others
• Atypical
• Mycoplasma, Chlamydia, Legionella, viruses

4
Agents causing atypical pneumonia

• Mycoplasma pneumoniae
• Chlamydia pneumoniae
• Legionella sp.
• Viruses

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Mycoplasma pneumoniae

• Outbreaks every 4-5 years
• Sporadic cases can be detected
• Predominantly in children and young adults

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Diagnostic of Mycoplasma pneumoniae

• Direct detection of microorganism
• Culture
• Antigen detection
• DNA detection (PCR)
• Antibody detection

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Direct detection of microrganism

• Culture
• Slow, less sensitive
• Antigen detection
• Not widely used, less sensitive
• DNA detection (PCR)
• Promising
• The main problem is a valid sample

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Antibody detection

• Complement binding reaction (CBR)
• Fourfold increase of antibody titre
• Best sensitivity and specificity
• Enzyme immunoassay (EIA)
• IgG, IgA, IgM classes
• Differences in results depending on manufacturer
  of a test

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Comparison of EIA tests

• Five kits from different manufacturers
• All sera tested in IgG, IgA, IgM classes
• Panel of CBR seroconversion and CBR negative
  sera

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Results

• Sensitivity
• IgA 68-97, IgM 87-97
• Specificity
• IgA 76-100, IgM 60-99
• PPV
• IgA 91-99, IgM 90-99
• NPV
• IgA 50-90, IgM 78-91

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Pitfalls in EIA testing

• High sensitivity was combined with low
  specificity and vice versa
• No manufacturer had excelent quality of tests for
  both IgA and IgM
• Correct diagnosis from the first sample could be
  done in approx. 40 of cases,

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Conclusion (Mycoplasma)

• It is essential to choose carefully not only
  manufacturer but also the test used.
• No approach is free of charge. You pay for high
  sensitivity with low specificity
• First sample testing leads to diagnosis in 40 of
  cases

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Chlamydia pneumoniae

• Occurs more frequently in older patients, can
  cause complications in patients with other
  diseases
• Outbreaks occur locally, with no typical
  periodicity
• Most cases are sporadic

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Diagnostic of Chlamydia pneumoniae

• Direct detection of microorganism
• Culture
• Antigen detection
• DNA detection
• Detecton of antibodies

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Direct detection of microorganism

• Culture
• difficult
• Antigen detection
• low sensitivity and specificity
• DNA detection
• Promising
• The main problem is valid sample

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Antibody testing

• EIA
• Mostly genus specific, less sensitive in early
  stage of infection, Ab detected long time after
  resolution of the disease
• Imunofluorescent test (MIF)
• golden standard, time and labour-consuming
• Immunoblott
• Confirmaton method

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Immunoblott results in detection of acute
infection

• Panel of 43 sera from patients with clinical and
  microbiological markers of acute Chlamydia
  pneumoniae infection
• Concordant results (MIF and IB) 63
• Negative or borderline IgA in IB 21
• IB negative, MIF positive 16
• Results of reconvalescent blood sample proved the
  diagnosis
• Infants with C. trachomatis respiratory tract
  infection (6) 100

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Immunoblott in detection of chronic Chlamydia
infection

• Tested on panel of 80 sera with several month
  persistence of IgG and IgA MIF antibodies to
  Chlamydia pneumoniae
• IB positive IgG and IgA 31
• IB positive IgG only 51
• IB negative 18

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Antibodies are not disease. To treat antibody
levels without corresponding illness is a serious
mistake. It leads to impropper use of antibiotics
and it is one of the causes of increasing ATB
resistance.
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Conclusion (Chlamydia)

• IB is a confirmatory method
• IB is less sensitive than MIF (can be negative in
  early phases of acute infection)
• Interpretation of the results should be based on
  laboratory and clinical data and on patients
  history
• So caled persistent infection is diagnostic
  problem. Only long term survey of patient and
  repeated testing may help

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Conclusions

• Diagnosis of Chlamydia pneumoniae and Mycoplasma
  pneumoniae is based mainly on antibody testing
• Culture and PCR have their limits (valid sample)
• Carefull choice of tests and interpretation of
  the results with reasonable knowledge of clinical
  data seems to be essential
• Without interpretation the results might be
  misleading