Chlamydophila species


Indications for Testing

  • C. pneumoniae – atypical pneumonia presentation
  • C. psittaci – atypical pneumonia and history of bird exposure

Laboratory Testing

  • Initial testing – CBC with differential
  • Serology
    • Order C. pneumoniae, M. pneumoniae and Legionella pneumophila concurrently; routine diagnostic tests to identify etiologic agent of outpatient pneumonia in adults is optional (Infectious Disease Society of America/American Thoracic Society)
    • Confirmed by paired serology for C. pneumoniae (four-fold elevation)
    • Order antibody panel if suspicious of C. psittaci
    • Performed using complement fixation, microimmunofluorescence, enzyme immunoassay
  • PCR – much more sensitive than culture and serology
  • Culture – difficult to grow atypical agents; positive culture confirms diagnosis

Imaging Studies

  • Chest x-ray – no distinctive chest x-ray pattern

Differential Diagnosis

Clinical Background

Chlamydophila is a genus of bacteria in the Chlamydiaceae family that causes atypical pneumonias, which may become life threatening.


  • Incidence – C. pneumophilia – 100/100,000 in U.S.
  • Age
    • C. pneumoniae – peak incidence is late childhood to young adulthood
      • ~50% of young adults in the U.S. will have evidence of past infection by age 20
      • Reinfection throughout life is common
  • Transmission
    • C. pneumoniae – respiratory secretions
      • May produce epidemics in close-quarter settings such as military barracks
    • C. psittaci – respiratory inhalation during exposure to infected birds (zoonoses)
      • Does not require prolonged contact with infected bird
      • May be an occupation-related disease


  • C. psittaci and C. pneumoniae are obligate, intracellular, gram-negative bacteria

Clinical Presentation

  • C. pneumoniae
    • Incubation – 7-10 days
    • Constitutional – leukocytosis and fever are often lacking; may resemble Mycoplasma pneumoniae infections
    • Pulmonary – bronchitis, pneumonia, exacerbations of chronic bronchitis and asthma
    • Upper respiratory tract – laryngitis, otitis media, sinusitis, pharyngitis
    • Dermatologic – erythema nodosum
    • Neurologic – meningitis (uncommon)
    • Cardiac – endocarditis, myocarditis (uncommon)
  • C. psittaci
    • Incubation – 7-14 days
    • Constitutional – fever, chills, headache, myalgias
    • Pulmonary – cough, pleural rub, rales, dyspnea, pneumonia
    • Gastrointestinal – diarrhea, nausea, anorexia, abdominal pain
    • Hepatitic – hepatitis
    • Dermatologic – faint macular rash may occur (Horder spots), erythema multiforme, erythema nodosum
    • Neurologic – cranial nerve palsies, cerebellar involvement, transverse myelitis, meningitis
    • Cardiac – endocarditis, myocarditis, pericarditis

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Chlamydia pneumoniae by PCR 0060715
Method: Qualitative Polymerase Chain Reaction

Confirm C. pneumoniae as infectious agent in nasal wash, nasopharyngeal aspirate, bronchoalveolar lavage (BAL) or pleural fluid

More sensitive than IFA and culture

Chlamydia Antibody Panel, IgG & IgM by IFA 0065100
Method: Semi-Quantitative Indirect Fluorescent Antibody

Differentiate between Chlamydophila species (C. psittaci, C. pneumoniae)

Differentiate early IgM response to infection from persistent low-level titer

Because of cross-reactivity, a C. pneumoniae-specific reaction will exhibit titers two-fold or greater than C. trachomatis or C. psittaci serology

Anti-chlamydial IgM antibody is very cross-reactive and will often represent titers to multiple, non-infecting chlamydial species

If results are equivocal, retest sera 2-3 weeks after first test
Mycoplasma pneumoniae Antibodies, IgG & IgM 0050399
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay
Testing to evaluate for acute mycoplasma infection    
Legionella pneumophila Antigen, Urine 0070322
Method: Qualitative Enzyme-Linked Immunosorbent Assay

Rapid diagnostic test for Legionella

Additional Tests Available
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

May help differentiate between bacterial and viral pneumonias

Chlamydia Antibody Panel, IgG by IFA 0065139
Method: Semi-Quantitative Indirect Fluorescent Antibody
Chlamydia Antibody Panel, IgM by IFA 0065105
Method: Semi-Quantitative Indirect Fluorescent Antibody
Mycoplasma pneumoniae by PCR 0060256
Method: Qualitative Polymerase Chain Reaction

Evaluate for Chlamydia infection

Legionella Species by Qualitative PCR 2010125
Method: Qualitative Polymerase Chain Reaction

Rapid diagnostic test for Legionella, particularly in patient partially treated with empirical antibiotics