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Copyright Notice & Disclaimer
Statement
Because several diseases affecting humans can be caused by other species of
Chlamydia, the disease resulting from the infection of humans with C.
psittaci is frequently referred to as psittacosis. Most C. psittaci
infections in humans result from exposure to psittacine birds.
During 1987-1996, 619 cases of psittacosis in humans were reported to the
Centers for Disease Control and Prevention (CDC) (2). Because the diagnosis of
psittacosis can be difficult, these 619 cases represent an underestimation of
the actual number of cases. During the 1980's, public health surveillance
indicated that exposure to caged pet birds accounted for 70% of the psittacosis
cases for which the source of infection was known; of these, owners of companion
birds or bird fanciers were the largest group of affected persons (43%). Pet-shop employees accounted for an additional 10% of cases. Other persons at
risk include pigeon fanciers and persons whose occupation places them at risk of
exposure (e.g., employees in poultry-slaughtering/processing plants,
veterinarians, veterinary technicians, laboratory workers, workers in avian
quarantine stations, farmers, and zoo workers). Because human infection can
result from transient exposure to infected birds or their contaminated
droppings, persons with no identified avocational or occupational risk may
become infected.
Human infection with C. psittaci usually occurs through the inhalation
of the organism aerosolized from respiratory secretions or dried feces of
infected birds. Other sources of exposure can include bird bites, mouth-to-beak
contact, and handling the plumage and tissure of infected birds. Brief exposures
can lead to symptomatic infection; therefore, history of contact with birds may
not be elicited from some patients with psittacosis.
C. psittaci from mammalian species can occasionally cause disease in
humans. Certain strains of C. psittaci infect sheep, goats, and cattle,
causing chronic infection of the reproductive tract, placental insufficiency,
and abortion in these species. Transmission of these strains to humans exposed
to birth fluids and placentas of infected animals has been reported. Feline
keratoconjunctivitis agent is a strain of C. psittaci that typically
causes rhinitis and conjunctivitis in cats. Transmission of this strain to
humans appears to occur rarely.
Human-to-human transmission has been suggested, but not proven. Standard
precautions are sufficient for patients with psittacosis and specific isolation
procedures (e.g., private room, negative pressure airflow, masks) are not
indicated.
Illness onset occurs following and incubation period of 5 to 14 days. The
severity of the disease resulting from C. psittaci infection ranges from
inapparent to systemic illness with severe pneumonia. Although mortality rates
of 15% to 20% were reported during the preantibiotic era, death occurs in <1%
of properly treated patients.
Cases of symptomatic infection are typically characterized by abrupt onset of
fever, chills, headache, malaise, and myalgia. A nonproductive cough usually
develops and may be accompanied by dyspnea and chest tightness. A
pulse-temperature dissociation, splenomegaly, and rash are sometimes observed
and are suggestive of psittacosis in patients with community-acquired pneumonia. Auscultatory findings may underestimate the extent of pulmonary involvement. Radiographic findings include lobar or interstitial infiltrates. The
differential diagnosis of psittacosis-related pneumonia includes infection with
Coxiella burnetti, Mycoplasma pneumodiae, Chlamydia pneumoniae,
Legionella spp, and respiratory viruses (e.g., influenza). C.
psittaci can affect organ systems other than the respiratory tract and
result in endocarditis, myocarditis, hepatitis, and fetal death has been
reported in pregnant women.
A patient is considered to have a confirmed case of psittacosis
if
- C. psittaci is cultured from clinical specimens or
- clinical illness is compatible with chlamydiosis and the antibody titer is
increased by greater than fourfold (i.e., to >32) as demonstrated by a
complement-fixation (CF) or microimmunofluorescence (MIF) test for C.
psittaci by either paired sera obtained at least 2 weeks apart or
detection of IgM antibody (i.e., >16) by MIF against C. psittaci.
A patient is considered to have a probable case of psittacosis
if there is
- a clinically compatible illness that is epidemiologically linked to a
confirmed case or
- a single antibody titer >32 by MIF or CF is present in at least one
serum speciment obtained after onset of symptoms.
These case definitions were established by CDC and the Council of State and
Territorial Epidemiologists for epidemiologic purposes (3). They should not be
used as sole criteria for establishing clinical diagnoses.
Return
to Psittacosis Index
Diagnosis almost always is established by using serologic methods in which
paired sera are tested for Chlamydia antibodies by CF test. However,
because Chlamydia CF antibody is not species specific, high CG titers
also may result from C. pneumoniae and Chlamydia trachomatis
infection. Acute- and convalescent-phase serum specimens should be obtained as
soon as possible after onset of symptoms and greater than or equal to 2 weeks
after onset of symptoms, respectively. Because treatment with tetracycline may
delay or diminish the antibody response, a third serum sample may help confirm
the diagnosis. All sera should be tested simultaneously at the same laboratory.
If indicated by epidemiologic and clinical history, MIF assays can be used to
distinguish C. psittaci infection from infection with other chlamydial
species. Information about laboratory testing is often available at state
laboratories. In humans, the infective agent can be isolated from sputum,
pleural fluid, or clotted blood during acute illness before treatment with
antibiotics.
Tetracyclines are the drugs of choice for treating psittacosis in humans;
most persons respond to oral therapy (100 mg of doxycycline administered twice a
day or 500 mg of tetracycline hydrochloride administered four times a day). For
initial treatment of severely ill patients, doxycycline hyclate may be
administered intravenously at a dosage of 4.4 mg/kg (2 mg/lb) body weight per
day divided into two daily infusions (up to 100 mg per dose). Tetracycline
hydrochloride may also be given intravenously (10-15 mg/kg body weight/day
divided into four daily doses), but a preparation for injection is no longer
available in the United States. Remission of symptoms usually is evident within
48-72 hours. However, relapse may occur, and treatment must continue for at
least 10-14 days after fever abates. Although its in vivo efficacy has not been
determined, erythromycin is probably the best alternative agent for persons for
whom tetracycline is contraindicated (e.g., children aged <9 years and
pregnant women).
Most states require physicians to report cases of psittacosis in humans to
the appropriate health authorities. Timely diagnosis and reporting may aid in
identifying the source of the infection and in controlling the spread of
disease. Because single-serum titers are both insensitive and nonspecific for
diagnosis of psittacosis, confirmation with paired acute- and convalescent-phase
sera is recommended.
Birds that are suspected sources of human infection should be referred to
veterinarians for evaluation and treatment. Local and state authorities may
conduct epidemiologic investigations and institute additional disease-control
measures.
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