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What is it?

This illness was named “Q (for query) fever” in 1937 when the first cases of the disease were reported but very little was known about it. Since then, the cause and routes of the disease have been discovered but the name has been retained.

Q fever is caused by an intracellular bacterium called Coxiella burnetii. The name is derived from the Australian and American researchers who discovered the microorganism. Macfarlane Burnet and Edward Derrick isolated it from patients in Queensland and Herald Cox recovered bacteria from ticks collected in Montana.

Characteristically, this bacterium has two states or phases. Bacteria obtained directly from patients are in phase I, but those obtained from laboratory cultures present in phase II.

Q fever can have acute or chronic stages and there is increasing recognition of a post Q Fever Fatigue Syndrome (QFS).

Acute Q fever has an incubation period of 15 to 25 days and commonly presents as an influenza-like illness with fever, severe headache often worst behind the eyes, rigors, drenching sweats, muscle pain and acute weight loss. There is usually some evidence of liver disease. In addition, acute infection can include pneumonia with a cough and chest pain. The acute illness lasts 2 to 6 weeks. About 20 per cent of acutely ill people may develop QFS lasting more than 6 months after resolution of the acute disease.

A small number of people who suffer acute Q fever will go on to develop chronic Q fever. This can occur months or years after acute illness. Most commonly chronic Q fever is a result of the organism infecting the heart valves (endocarditis) however other sites of infection such as bone (osteomyelitis) or the liver (hepatitis) are recognised. People with pre-existing heart disease or underlying immunosuppression are at greatest risk of developing chronic Q fever after an acute episode.

Disease is endemic to much of the world including Australia. Diagnosis of Q fever is not easy, as signs and symptoms are non-specific. A history of exposure to cattle, sheep or goats may be a useful pointer to the diagnosis, but there are many other routes of transmission.


Last Review Date: October 13, 2016