33-40: Chlamydophila Psittaci & Psittacosis (Ornithosis)

ESSENTIALS OF DIAGNOSIS

GENERAL CONSIDERATIONS

Psittacosis is acquired from contact with birds (parrots, parakeets, pigeons, chickens, ducks, and many others), which may or may not be ill. The history may be difficult to obtain if the patient acquired infection from an illegally imported bird.

CLINICAL FINDINGS

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. Endocarditis, which is culture-negative, may occur. The radiographic findings in typical psittacosis 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.

The organism is rarely isolated from cultures. The diagnosis is usually made serologically; antibodies appear during the second week and can be demonstrated by complement fixation or immunofluorescence. Antibody response may be suppressed by early chemotherapy.

DIFFERENTIAL DIAGNOSIS

The illness is indistinguishable from viral, mycoplasmal, or other atypical pneumonias except for the history of contact with birds. Psittacosis is in the differential diagnosis of culture-negative endocarditis.

TREATMENT

Treatment is with doxycycline 100 mg orally twice daily for 10–21 days. Erythromycin, 500 mg orally every 6 hours, or azithromycin, 500 mg orally on day 1, and then 250 mg once daily for 4 days, may be effective as well.