Q fever

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Q fever is caused by infection with Coxiella burnetii. Coxiella burnetii is a zoonotic bacteria, meaning it is transmitted from animals to humans. It was first described in 1935, in abattoir workers in Australia, as a disease of unknown origin.  The disease was therefore called “query fever”.  

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The incubation period is 2 to 8 weeks. Infection is asymptomatic in at least half of cases.  

A person with acute Q fever can present with a variety of symptoms. Commonly reported signs include:  

• fever (lasting 7 to 14 days)  
• chills/sweats (requiring changes of clothes and bed linen) 
• severe headache (especially behind the eyes) 
• photophobia (sensitivity to light) 
• extreme fatigue and myalgia (muscle aches) 
• anorexia and weight loss 
• diarrhoea and nausea 
• cough. 

A minority of infected cases (1% or less) may develop pericarditis (inflammation of the lining of the heart muscle), myocarditis (inflammation of the heart muscle) or neurologic complications such as meningoencephalitis (inflammation of the meninges, the layers of tissue that cover the brain) and encephalomyelitis (inflammation of the myelin in the brain and spinal cord, the protective coating of nerves). Pneumonia and hepatitis can be seen in more severe acute infections.  Q fever infection during pregnancy can lead to premature delivery, intrauterine foetal growth restriction or miscarriage. 

Q fever infection can result in chronic disease, most commonly endocarditis (inflammation of the inner lining of the chambers and valves of the heart). Osteomyelitis (inflammation of the bone), vascular infection (infection of arteries and veins), aortic graft infection, chronic hepatitis (inflammation of the liver), and inflammatory lesions of the spleen and lungs can also occur. Chronic disease predominantly occurs in those with predisposing conditions like heart valve issues, vascular abnormalities, and immunosuppression. 

Q fever fatigue syndrome (QFS) occurs in approximately 10 to 15% of people who contract Q fever and refers to symptoms that continue more than 12 months after the acute infection. Typical features of QFS include extreme fatigue, body aches, concentration and memory problems, and headaches. 

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Transmission occurs via the inhalation of infected aerosols or contaminated soil, dusts or water droplets. The bacteria is shed by infected animals through their milk, urine, faeces, placental tissue or birth fluids. Infection can also occur via contact with wool or other fomites (contaminated items) and through wounds or splashes to the eye. 

Bacterial reservoirs for human infection primarily include cattle, sheep, and goats; however, other animals can also be infected. Ticks are an important vector in the transmission cycle among animals but are not involved in human transmission. 

Coxiella burnetii is highly infectious and can survive in air, soil, water and dust for more than a year. Pasteurisation can inactivate the bacteria. 

Dịch tễ học 

People at highest risk of exposure to Q fever are those in close contact with animals and animal products. This includes abattoir and other meat industry workers, farmers, veterinarians, stockyard workers, shearers, animal transporters and many others exposed to ruminants or their products. 

The reported incidence of Q fever in Australia is relatively low, with approximately 500 cases per year between 2017 and 2022. However, a 2019 study of NSW and QLD blood donors estimated that 30% to 40% of people with Q fever in the past had not been diagnosed with the disease. Coxiella burnetii has been found in most countries that have conducted surveillance (exceptions include New Zealand, Norway, Iceland and French Polynesia). 

Phòng ngừa 

In addition to appropriate workplace design, safe work practices and land use planning, vaccination has an important role to play in reducing transmission of Coxiella burnetii to humans. 

Q-Vax is recommended for those aged over 15 years, in specific high-risk occupational groups. Vaccination requires a single dose only to be administered subcutaneously. Booster doses are not recommended. 

Q-Vax has been available in Australia since 1989, with efficacy estimated at 83–100%.  

Precautions and contraindications 

Before vaccination, both serological (blood) and skin testing must be performed. If previous infection is confirmed, vaccination is contraindicated due to the risk of adverse events.  

People with a known egg allergy who require vaccination should be referred to an immunologist, allergist or specialist immunisation service.  

Q fever vaccination is not routinely recommended in pregnancy or if breastfeeding. 

Vaccination is not recommended in those aged under 15 years due to a lack of safety and efficacy data for this age group. 

Phản ứng phụ 

Common side effects following Q fever vaccination are phản ứng tại chỗ tiêm, headache, fever, chills and sweating. Induration (hard, tight swelling) or oedema (fluid build-up) at the injection site is an uncommon side effect and occurs in less than 1% of recipients. 

Documentation

Administration of Q fever vaccines must be reported to the Đăng ký Chủng ngừa Úc (AIR). 

Historically the Q fever Register has stored information on individuals’ Q fever immune status, including vaccination and test results.  From 15 April 2024, the Q fever Register has closed. Until 30 June 2025, those with an existing Q fever Register record can access their vaccination/natural immunity eStatement via the Register and take it to an immunisation provider to be reported to AIR.

• The Department of Health: Q fever
• Australian Immunisation Handbook: Q fever chapter
• Health Direct Australia: Q fever
• Australian Q fever Register