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Psittacosis / Ornithosis (Chlamydophila psittaci)
1990 Case Definition

NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. Surveillance case definitions are not intended to be used by healthcare providers for making a clinical diagnosis or determining how to meet an individual patient’s health needs.

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.