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Q Fever (Coxiella burnetii)
1999 Case Definition
Clinical description
Acute infection:
A febrile illness usually accompanied by rigors, myalgia, malaise,
and retrobulbar headache. Severe disease can include acute hepatitis,
pneumonia, and meningoencephalitis. Clinical laboratory findings
may include elevated liver enzyme levels and abnormal chest film
findings. Asymptomatic infections may also occur.
Chronic infection:
Potentially fatal endocarditis may evolve months to years after
acute infection, particularly in persons with underlying valvular
disease. A chronic fatigue-like syndrome has been reported in
some Q fever patients.
Laboratory criteria for diagnosis
- Fourfold or greater change in antibody titer
to C. burnetii phase II or phase I antigen in paired
serum specimens ideally taken 3-6 weeks apart, or,
- Isolation of C. burnetii from a clinical
specimen by culture, or
- Demonstration of C. burnetii in a
clinical specimen by detection of antigen or nucleic acid.
Case classification
Probable: a clinically
compatible or epidemiologically linked case with a single supportive
Immunoglobulin G (IgG) or Immunoglobulin M (IgM) titer. Cutoff
titers are determined by individual laboratories. CDC tests for
IgG antibodies with an indirect immunofluorescence assay (IFA),
and uses a titer of 1:128 as the cutoff for significant antibody.
Confirmed: a clinically compatible or
epidemiologically linked case that is laboratory confirmed.
See also:
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