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Psittacosis / Ornithosis (Chlamydophila psittaci)
1990 Case Definition

Clinical Description

An illness characterized by fever, chills, headache, photophobia, lower or upper respiratory disease, and myalgia

Laboratory Criteria for Diagnosis

  • Isolation of Chlamydia psittaci from a clinical specimen, OR
  • Fourfold or greater increase in psittacosis complement-fixing (CF) antibody titer (greater than or equal to 32) between two serum specimens obtained greater than or equal to 2 weeks apart and studied at the same laboratory

Case Classification


Probable A clinically compatible illness that is epidemiologically linked to a confirmed case, or with supportive serology (i.e., a psittacosis CF titer of greater than or equal to 32 in one or more serum specimens obtained after onset of symptoms)


A clinically compatible illness that is laboratory confirmed


The serologic findings noted above may also occur as a result of infection with Chlamydia trachomatis or Chlamydia pneumoniae.