Psittacosis: Diagnosis and Treatment
Most Likely Diagnosis
The most likely diagnosis is psittacosis (parrot fever), caused by Chlamydia psittaci, given the classic triad of abrupt fever with severe headache, dry cough, and recent parrot exposure. 1
Clinical Presentation
The patient's presentation is textbook for psittacosis:
- Abrupt onset of fever, chills, severe headache, malaise, and myalgias are the hallmark symptoms 1
- A nonproductive (dry) cough typically develops, often accompanied by breathing difficulty and chest tightness 1
- The incubation period is typically 5-14 days after bird exposure, though longer periods have been reported 1
- Even brief, transient exposure to infected birds or their contaminated droppings can produce symptomatic infection 2
Suggestive Clinical Signs
- Pulse-temperature dissociation (fever without elevated pulse), splenomegaly, and rash are sometimes observed and strongly suggest psittacosis in patients with community-acquired pneumonia 1
- Auscultatory findings often underestimate the extent of pulmonary involvement 1
- Radiographic findings typically show lobar or interstitial infiltrates 1
First-Line Treatment
Doxycycline is the drug of choice for psittacosis and should be initiated immediately upon clinical suspicion, even before laboratory confirmation. 3, 4
Treatment Protocol
- Early and specific treatment with tetracycline antibiotics, specifically doxycycline, should be started as soon as psittacosis is suspected 4
- The CDC explicitly recommends prompt treatment with doxycycline without waiting for laboratory confirmation 4
- With appropriate treatment, less than 1% of properly treated patients die, compared to 15-20% mortality in the pre-antibiotic era 1
Alternative Therapy
- Second-line options include erythromycin or azithromycin for patients who cannot tolerate tetracyclines 5
Diagnostic Confirmation
While treatment should not be delayed, diagnostic confirmation can be pursued:
- Paired sera tested for Chlamydia antibodies by complement-fixation test showing ≥4-fold rise to a titer ≥32 confirms the diagnosis 3
- Culture of C. psittaci from respiratory secretions is definitive but not routinely available 1
- IgM antibody detected by microimmunofluorescence (MIF) to a reciprocal titer ≥16 confirms acute infection 1
Differential Diagnosis
The differential diagnosis of psittacosis-related pneumonia includes Coxiella burnetii (Q fever), Mycoplasma pneumoniae, Chlamydia pneumoniae, Legionella species, and respiratory viruses such as influenza. 1
Potential Complications
Psittacosis can affect organ systems beyond the respiratory tract:
- Endocarditis, myocarditis, hepatitis, arthritis, keratoconjunctivitis, and encephalitis may occur 1
- Severe illness with respiratory failure, thrombocytopenia, hepatitis, and fetal death has been reported in pregnant women 1
Common Pitfalls
- Some patients may not recall or report bird contact because even brief exposures can cause infection 1
- The disease is difficult to diagnose and often goes unreported, leading to underestimation of actual case numbers 1
- Psittacosis should be considered in any patient with atypical pneumonia accompanied by severe headache, especially with bird exposure history 6