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CDC Diagnostic Criteria for Psittacosis (Ornithosis)

1996 Case Definition

Clinical description

An illness characterized by fever, chills, headache, photophobia, cough, and myalgia

Laboratory criteria for diagnosis

  • Isolation of Chlamydia psittaci from respiratory secretions, or
  • Fourfold or greater increase in antibody against C. psittaci by complement fixation (CF) or microimmunofluorescence (MIF) to a reciprocal titer of greater than or equal to 32 between paired acute- and convalescent-phase serum specimens, or
  • Presence of immunoglobulin M antibody against C. psittaci by MIF to a reciprocal titer of greater than or equal to 16

Case classification

  • Probable: a clinically compatible case that is epidemiologically linked to a confirmed case or that has supportive serology (e.g., C. psittaci titer of greater than or equal to 32 in one or more serum specimens obtained after onset of symptoms)
  • Confirmed: a clinically compatible case that is laboratory confirmed


The serologic findings by CF also may occur as a result of infection with Chlamydia pneumoniae or Chlamydia trachomatis. The MIF might be more specific for infection with C. psittaci, but experience with and availability of this newer test are more limited.

Related Criteria

Case Definition of Staphylococcal Toxic Shock Syndrome (TSS)

Case Definition of Streptococcal Toxic-Shock Syndrome (Streptococcal TSS) and Necrotizing Fasciitis




  1. Compendium of measures to control Chlamydia psittaci infection among humans (psittacosis) and pet birds (avian chlamydiosis), 2000. Centers for Disease Control and Prevention. MMWR Recomm Rep. 2000 Jul 14;49(RR-8):3-17. [Medline]

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Created: September 27, 2005
Last Modified: 10-23-2010



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