Introduction

Q fever is an infectious disease usually acquired from working in close quarters with live animals. It is caused by the Gram-negative bacterium Coxiella burnetii. 

It was named “q” (for query) fever in 1937 in Queensland, Australia, and the infective organism was subsequently simultaneously identified in the US and Australia. It has now been identified almost world-wide, except in New Zealand and Antarctica.

Due to non-specific symptoms is often difficult to diagnose. It is widespread in the animal kingdom, but found mainly in cattle, sheep and goats, although almost any wild animal can be infected. It is most commonly transmitted to humans through inhalation.

It causes both an acute and chronic illness, but is thought to be widely under-diagnosed in the acute phase. The chronic disease occurs in <5% of cases, but can be fatal.

A vaccine exists, although the practicalities of immunisation can be somewhat tricky.

Epidemiology

  • Thought to be vastly under-diagnosed due to the asymptomatic nature of the majority of presentations
  • Most common in Asutralia –¬†about 2.5 cases per 100 000 per year
    • 6 per 100 000 in QLD
    • 3 per 100 000 in NSW
    • Rare in other parts of Australia
  • In Europe and the USA, there are about 0.1 cases per 100 000 per year
    • One study in the UK showed that about 21% of dairy herds were infected
    • Animals rarely become ill, but do show increased rate of abortion and stillbirth when infected
  • There are times of outbreak. The largest outbreak recorded was in the Netherlands in 2010, when 4,000 cases were reported
  • Most commonly affects middle aged males (likely due to this demographic being most likely to work with livestock or in slaughterhouses)

Transmission

Coxiella burnetti bacteria are shed in most bodily fluids, but particularly in birth products. As such, it may be easily widely spread in the environment in manure. It can also be found living in dust and soil, where it may survive for many months or even years.

It is most commonly transmitted to humans through inhalation of dust or contaminated other aerosols.

  • It can also be contracted by drinking raw milk
  • It can also be transmitted through cuts from infected sharp objects, or needle stick injuries from animals
  • It may also be transmitted from human to human via sexual transmission, vertical transmission, blood products and autopsy of infected cadavers

It has an incubation period of 2-3 weeks, sometimes up to 6 weeks.

Presentation

  • 60% of cases are asymptomatic
  • Infection typically provides lifelong immunity

Acute infection

  • Flu-like symptoms
    • Fevers – can last up to 10 days
    • Myalgia
    • Headache
    • Nausea
    • Cough
    • Rash –¬†maculopapular
  • Hepatitis
  • Pneumonia
    • More commonly an atypical type
  • Rarely
    • Myocarditis
    • Pericarditis
    • Neurological complications
  • Mortality in acute Q fever <2%

Chronic infection

  • Anywhere from one month to several years after primary infection
  • Fever
  • Hepatomegaly and splenomegaly (50%)
  • Clubbing
  • Abdominal pain
  • Chest pain
  • Night sweats
  • Endocarditis
    • Occurs in about 2% of patients
    • Fatal if untreated
    • If treated, 10 year mortality is about 20%
  • Bone and joint infections
    • <1% of cases
    • Common when Q fever occurs in children (although children are rarely infected)
  • Vascular infections
    • Especially at sites of previous aneurysm or graft
    • Mortality rates of about 20-25%

Q fever fatigue syndrome

QFS affects about 10-15% of patients. It is a chronic syndrome that occurs after acute infection, and includes on-specific fatigue type symptoms such as:

  • Lethargy
  • Fatigue
  • Myalgia
  • Arthralgia
  • Sleep disturbance
  • Memory issues

Diagnosis

  • Requires a level of clinical suspicion to be considered as a differential
  • Culture for coxiella burnetti should be avoided
    • It is difficult to culture
    • When it is successfully cultured it is a high risk for laboratory technicians
    • When requesting a blood culture and Q fever is a differential this should be clearly states on the referral form
  • Q fever serology¬†or¬†Q fever PCR¬†are the preferred methods of testing
    • These are usually both performed in conduction with one-another
    • PCR results are quick, but less accurate
    • Serology testing often requires x2 samples, 7 days apart to confirm the diagnosis
      • Seroconversion takes up to 3 weeks after symptom onset
    • PCR can be done on a single sample but has a higher false negative rate
    • Consider consulting an infectious diseases specialist for advice on diagnosis if Q fever is suspected
  • FBC usually raised
  • CRP usually raised
  • LFTs may be elevated
  • Transoesophageal echo¬†should be considered in all patients thought to be suffering from chronic Q fever
  • CXR – if any evidence of pneumonia

Management

  • Docycline 100mg BD for 14 days is the recommended treatment
  • Refer to infectious diseases specialist
  • Chronic Q fever
    • Requires long-term antibiotics – often 18 months or more
      • Taking doxycycline for this long is unpleasant. It frequently causes oesophagi’s and may also cause photosensitivity. Patients should avoid air products within 2 hours of taking doxycycline.
    • Involve infectious diseases specialist as soon as possible
    • If any prosthetic implants (e.g. prosthetic heart valves, aneurysm repairs) or if immunocompromised, MDT specialist care should be sought as soon as possible
    • Measure antibody titres every 6 months

Vaccination

Q fever vaccine (Q-Vax(R)) has been available since 1989. Efficacy 83-100%.

The vaccine is recommended to anyone at risk of Q fever – including anyone who works with live animals or untreated raw animal products.

  • Hypersensitivity reaction can¬†occur¬†if the vaccine is given to anybody who has previously been infected with Q fever or had previous vaccination
  • As such, pre-vaccination testing is required for anybody wishing to be vaccinated. This usually includes:
    • Detailed history and review of medical records for any previous vaccinations or diagnoses
    • Skin testing for cellular immunity
      • Similar to the TB skin test
      • Skin (scratch) and serological testing done on the same day
      • Patient need to return 7 days alter to have the skin lesion examined for signs of reactivity
    • Serological testing
      • Both skin and serological testing should be used together
  • Not recommended for those <15 or during pregnancy
  • Once skin and serological testing confirms no previous infection or vaccination, then a single dose of the vaccine is all that is needed.

Bioterrorism

Q fever is considered important as a potential bioterrorism agent. It is very stable in the natural environment, highly infectious and an aerosol agent, could easily be produced in large quantities and can cause serious disease.

References

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