Clinical Features: In humans, fever, chills, headache, muscle aches, and a dry cough. Pneumonia is often evident on chest x-ray.

Etiologic Agent: Chlamydia psittaci, a bacterium

Incidence: Since 1996, fewer than 50 confirmed cases were reported in the United States each year. Many more cases may occur that are not correctly diagnosed or reported.

Sequelae: Endocarditis, hepatitis, and neurologic complications may occasionally occur. Severe pneumonia requiring intensive-care support may also occur. Fatal cases have been reported.

Transmission: Infection is acquired by inhaling dried secretions from infected birds. The incubation period is 5 to 19 days. Although all birds are susceptible, pet birds (parrots, parakeets, macaws, and cockatiels) and poultry (turkeys and ducks) are most frequently involved in transmission to humans.

Risk Groups: Bird owners, pet shop employees, and veterinarians. Outbreaks of psittacosis in poultry processing plants have been reported.

Surveillance: Psittacosis is a reportable condition in most states.

Trends: Annual incidence varies considerably because of periodic outbreaks. A decline in reported cases since 1988 may be the result of improved diagnostic tests that distinguish C.psittaci from more common C. pneumoniae infections.

Challenges: Diagnosis of psittacosis can be difficult. Antibiotic treatment may prevent an antibody response, thus limiting diagnosis by serologic methods. Infected birds are often asymptomatic. Tracebacks of infected birds to distributors and breeders often is not possible because of limited regulation of the pet bird industry.