Psittacosis (Ornithosis) Case Definition

This document contains the case definitions for psittacosis which is nationally notifiable within Australia. This definition should be used to determine whether a case should be notified.

Page last updated: 11 May 2018

Version Summary of changes Last reviewed Implementation date
1.0 Initial case definition 2004 2004
  • Confirmed cases no longer require epidemiological evidence.
  • Complement fixation has been removed from laboratory suggestive evidence and included as laboratory definitive evidence.
  • Clinical evidence includes ‘not able to be explained by an alternative diagnosis’.
  • Proximity to an outbreak has been removed from epidemiological evidence and replaced by contact with a confirmed human or animal case.
  • Footnote included to assist in the interpretation of psittacosis serology.
2017 1 July 2018


Both confirmed cases and probable cases should be notified.

Confirmed case

A confirmed case requires laboratory definitive evidence AND clinical evidence

Probable case

A probable case requires laboratory suggestive evidence AND clinical evidence AND epidemiological evidence.

Laboratory definitive evidence

A seroconversion or fourfold or greater rise in either immunoglobulin G (IgG) antibody by microimmunofluorescence (MIF) or complement fixation (CF) antibody against Chlamydophila psittaci - between acute and convalescent sera (collected at least two weeks later) tested in parallel.1


Detection of C. psittaci by nucleic acid testing.


Isolation of C. psittaci by culture.

Laboratory suggestive evidence

Detection of IgM or single high IgG antibody titre2 to C. psittaci by MIF


A single high C. psittaci CF antibody titre.2

Clinical evidence



AT LEAST TWO of the following: fever, headache, myalgia, rigors, dry cough or dyspnoea.


Not explained by an alternative diagnosis

Epidemiological evidence

Direct or indirect exposure to birds or bird products, or contact with a confirmed human or animal case.

  1. C. psittaci MIF antibody is more specific than CF antibody. However, positive serologic findings by both MIF and CF may occur as a result of infection with other Chlamydia species and should be interpreted with caution. This is most likely to occur with primary Chlamydophila pneumoniae infection from 5-15 years of age. Chlamydia spp. infection in those < 5 years of age may not produce a MIF or CF serological response.
  2. MIF IgG antibody can persist for years whereas CF antibody diminishes over months following Chlamydia spp. infection

In this section