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Key Features

Essentials of Diagnosis

  • Fever, chills, and cough; headache common

  • Atypical pneumonia with slightly delayed appearance of signs of pneumonitis

  • Contact with infected psittacine bird 7–15 days previously

  • Isolation of chlamydiae or rising titer of complement-fixing antibodies

General Considerations

  • Etiologic agent is Chlamydia psittaci, a bacterium

  • Infection is acquired by inhaling dried secretions from infected psittacine birds (parrots, parakeets, pigeons, chickens, ducks, and many others), which may or may not appear ill

  • The incubation period is 6–19 days

  • Exposure history may be difficult to obtain if the patient acquired infection from an illegally imported bird

Clinical Findings

Symptoms and Signs

  • The onset is usually rapid, with fever, chills, myalgia, dry cough, and headache

  • Signs include temperature-pulse dissociation, dullness to percussion, and rales

  • Pulmonary findings may be absent early

  • Dyspnea and cyanosis may occur later

  • Culture-negative endocarditis

Differential Diagnosis

  • Other atypical pneumonia (eg, viral pneumonia, Mycoplasma pneumoniae, Chlamydophila pneumoniae)

  • Unusual presentations of typical bacterial pneumonia

  • Hypersensitivity pneumonitis


Laboratory Tests

  • The diagnosis is usually made serologically by a rise in titer of complement-fixing antibody in convalescent versus acute serum

  • Antibodies appear during the second week

  • Antibody response may be suppressed by early chemotherapy


  • The radiographic findings are those of atypical pneumonia, which tends to be interstitial and diffuse in appearance, though consolidation can occur

  • Psittacosis is indistinguishable from other bacterial or viral pneumonias by radiography



  • Tetracycline, 500 mg every 12 hours intravenously or orally, or doxycycline, 100 mg every 12 hours orally, for 14–21 days

  • Erythromycin, 500 mg every 6 hours orally, may also be effective



  • Endocarditis, hepatitis, and neurologic complications may occasionally occur

  • Severe pneumonia requiring intensive care support may also occur

  • Fatal cases have been reported


  • Traceback of infected birds to distributors and breeders often is not possible because of limited regulation of the pet bird industry


  • Excellent with early treatment


Hogerwerf  L  et al. Chlamydia psittaci (psittacosis) as a cause of community-acquired pneumonia: a systematic review and meta-analysis. Epidemiol Infect. 2017;145:3096.
[PubMed: 28946931]  

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