Chlamydophila species

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

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

Laboratory Testing

  • Chlamydophila pneumoniae infection (CDC, 2014)
  • Psittacosis (CDC, 2014)
  • Initial testing
    • CBC with differential
  • Serology
    • Atypical pneumonia presentation
      • 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)
      • PCR – much more sensitive than culture and serology
      • Culture – difficult to grow atypical agents; positive culture confirms diagnosis
    • Suspicion for C. psittaci
      • Order antibody panel if suspicious of C. psittaci
      • Performed using complement fixation, microimmunofluorescence, enzyme immunoassay

Imaging Studies

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

Differential Diagnosis

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


  • Incidence
  • 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, prisons
    • C. psittaci – respiratory inhalation of dried secretions 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 – cough, 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 – 5-19 days
    • Constitutional – fever, chills, headache, myalgias
    • Pulmonary – dry 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
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.

Chlamydia pneumoniae by PCR 0060715
Method: Qualitative Polymerase Chain Reaction

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


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

Legionella pneumophila Antigen, Urine 0070322
Method: Qualitative Enzyme-Linked Immunosorbent Assay

General References

Blasi F, Tarsia P, Aliberti S. Chlamydophila pneumoniae. Clin Microbiol Infect. 2009; 15(1): 29-35. PubMed

Burillo A, Bouza E. Chlamydophila pneumoniae. Infect Dis Clin North Am. 2010; 24(1): 61-71. PubMed

Cunha BA. The atypical pneumonias: clinical diagnosis and importance. Clin Microbiol Infect. 2006; 12 Suppl 3: 12-24. PubMed

Forgie S, Marrie TJ. Healthcare-associated atypical pneumonia. Semin Respir Crit Care Med. 2009; 30(1): 67-85. PubMed

Johansson N, Kalin M, Tiveljung-Lindell A, Giske CG, Hedlund J. Etiology of community-acquired pneumonia: increased microbiological yield with new diagnostic methods. Clin Infect Dis. 2010; 50(2): 202-9. PubMed

Kumar S, Hammerschlag MR. Acute respiratory infection due to Chlamydia pneumoniae: current status of diagnostic methods. Clin Infect Dis. 2007; 44(4): 568-76. PubMed

Villegas E, Sorlózano A, Gutiérrez J. Serological diagnosis of Chlamydia pneumoniae infection: limitations and perspectives. J Med Microbiol. 2010; 59(Pt 11): 1267-74. PubMed

Wolf J, Daley AJ. Microbiological aspects of bacterial lower respiratory tract illness in children: atypical pathogens. Paediatr Respir Rev. 2007; 8(3): 212-9, quiz 219-20. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Kendall BA, Tardif KD, Schlaberg R. Chlamydia trachomatis L serovars and dominance of novel L2b ompA variants, U.S.A. Sex Transm Infect. 2014; 90(4): 336. PubMed

Medical Reviewers

Last Update: August 2016