Diagnosis and Management of Psittacosis
Diagnosis
Psittacosis diagnosis relies primarily on serologic testing with paired acute and convalescent sera obtained at least 2 weeks apart, demonstrating a fourfold or greater rise in antibody titer to ≥32 by complement fixation (CF) or microimmunofluorescence (MIF) testing. 1
Clinical Presentation to Recognize
- Respiratory symptoms: Nonproductive cough, breathing difficulty, chest tightness with pneumonia (lobar or interstitial infiltrates on imaging) 1
- Systemic features: Abrupt onset of fever, chills, headache, malaise, and myalgia after 5-14 day incubation period 1
- Suggestive findings: Pulse-temperature dissociation (fever without elevated pulse), enlarged spleen, and rash 1
- Extrapulmonary manifestations: Endocarditis, myocarditis, hepatitis, arthritis, keratoconjunctivitis, encephalitis 1
- High-risk exposure: Bird owners, veterinarians, poultry workers, pet shop employees 1, 2
Diagnostic Testing Algorithm
Confirmed case requires compatible clinical illness PLUS one of: 1
- Culture of C. psittaci from respiratory secretions, sputum, pleural fluid, or clotted blood (rarely performed due to technical difficulty and safety concerns) 1
- Fourfold or greater antibody rise to reciprocal titer ≥32 between paired sera (acute and convalescent at ≥2 weeks apart) by CF or MIF 1
- IgM antibody titer ≥16 by MIF 1
Probable case requires compatible clinical illness PLUS: 1
- Epidemiologic link to confirmed case, OR
- Single antibody titer ≥32 by CF or MIF in post-symptom serum
Important Diagnostic Caveats
- CF antibody is NOT species-specific: High titers can result from C. pneumoniae or C. trachomatis infections 1
- Antibiotic treatment delays antibody response: Consider obtaining a third serum sample if initial paired sera are negative 1
- All sera must be tested simultaneously at the same laboratory for accurate comparison 1
- PCR testing offers rapid, specific alternative: Can distinguish C. psittaci from other chlamydial species when epidemiologic and clinical history suggest psittacosis 1
- Contact state public health laboratories for testing availability, as few commercial laboratories differentiate Chlamydia species 1
Management
Treat all suspected psittacosis cases with doxycycline 100 mg orally twice daily for at least 10-14 days after fever resolves, as tetracyclines are the drugs of choice and symptoms typically improve within 48-72 hours. 1, 3
Treatment Regimens
Standard oral therapy: 1
- Doxycycline 100 mg PO twice daily, OR
- Tetracycline hydrochloride 500 mg PO four times daily
Severe illness requiring IV therapy: 1
- Doxycycline hyclate 4.4 mg/kg/day IV divided into two infusions (maximum 100 mg per dose), OR
- Tetracycline hydrochloride 10-15 mg/kg/day IV 1
Alternative for contraindications (children <9 years, pregnant women): 1
- Erythromycin (in vivo efficacy not definitively established but considered best alternative) 1
Critical Management Points
- Duration: Continue treatment for minimum 10-14 days AFTER fever abates to prevent relapse 1
- Response timeline: Expect symptom remission within 48-72 hours; if no improvement, reconsider diagnosis 1
- Relapse risk: Can occur if treatment duration inadequate 1
- Mortality with proper treatment: <1% (compared to 15-20% pre-antibiotic era) 1
Special Populations
Pregnant women: 1
- At risk for severe illness with respiratory failure, thrombocytopenia, hepatitis, and fetal death
- Use erythromycin as tetracyclines are contraindicated 1
Infection Control and Reporting
- Person-to-person transmission is rare: Standard precautions sufficient; isolation, negative pressure rooms, and masks NOT indicated 1
- Report to health authorities: Most states require physician reporting to identify infection sources and control spread 1
- Investigate bird sources: Refer suspected source birds to veterinarians; local/state authorities may conduct epidemiologic investigations 1
- No prophylaxis for contacts indicated due to rarity of person-to-person transmission 1