Chlamydophila species

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

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

Indications for Testing

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

Laboratory Testing

  • Chlamydophila pneumoniae infection (CDC, 2016)
  • Psittacosis (CDC, 2016)
  • Initial testing
    • CBC with differential
  • PCR
    • Much more sensitive than culture and serology
  • Serology
    • Atypical pneumonia presentation
      • Order C. pneumoniae, Mycoplasma pneumoniae and Legionella pneumophila concurrently; routine diagnostic tests to identify etiologic agent of outpatient pneumonia in adults are optional (Infectious Disease Society of America/American Thoracic Society)
      • Confirmed by paired serology for C. pneumoniae (4-fold elevation)
  • Culture
    • Difficult to grow atypical agents; positive culture confirms diagnosis
    • Suspicion for C. psittaci
      • Order antibody panel
      • Performed using complement fixation, microimmunofluorescence, enzyme immunoassay

Imaging Studies

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

Differential Diagnosis


  • Incidence
    • Chlamydophila pneumophilia – overall incidence unknown (CDC, 2015)
    • Chlamydophila psittaci – rare in U.S.; zoonotic disease
  • Age
    • Chlamydophila 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
      • 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


Limited value in the diagnosis of most oculogenital (eg, eyes, genitalia) chlamydial infections

Mycoplasma pneumoniae Antibodies, IgG & IgM 0050399
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

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

Explify Respiratory Pathogens by Next Generation Sequencing 2013694
Method: Massively Parallel Sequencing


Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell D, Dean NC, Dowell SF, File TM, Musher DM, Niederman MS, Torres A, Whitney CG, Infectious Diseases Society of America, American Thoracic Society. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis. 2007; 44 Suppl 2: S27-72. PubMed

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: October 2017