Overview
Q fever is an infection caused by Coxiella burnetti, a rickettsia and Gram-negative bacteria, often acquired from the inhalation of dust from infected animals such as cattle and sheep. It is characterised by a sudden onset of fever and headaches and can cause atypical pneumonia.
Its name comes from ‘Query fever’, which came from the first clinician in Australia who investigated an outbreak of fever affecting employees working in a Brisbane abattoir.
Pathophysiology
Upon being inhaled, Coxiella burnetti proliferates within macrophages and monocytes, avoiding phagocytosis. Infected pulmonary macrophages can spread the infection to other organs including the liver, spleen, and bone marrow. The immune response leads to the formation of non-necrotising granulomata in the liver and bone marrow (doughnut granulomata), leading to organ dysfunction.
The degree of infection depends on how much bacteria is present and the immune response. In some people, infected monocytes produce interleukin 10 (IL-10), which reduces the ability of macrophages to kill the pathogen, resulting in more severe and persistent disease. People at risk of severe disease include pregnant people, pre-existing cardiovascular disease, HIV, and immunosuppressive states.
Epidemiology
- Q fever is rare in the UK, even in people who work with animals, with around 904 cases between 2000 and 2015
Presentation
Overview
Symptoms usually occur 2-3 weeks post-exposure. Features include:
- A flu-like prodrome lasting >2 weeks with fever, headaches, malaise, and myalgia
- Atypical pneumonia may occur
- Elevated transaminase results may be seen on liver function tests
- Rarely, it can cause infective endocarditis – usually in people with existing heart disease
In some people, they can develop persistent symptoms lasting >6 months.
Investigations
Investigation findings can include:
- Liver function tests (LFTs): may show elevated transaminases and alkaline phosphatase
- Serology or polymerase chain reaction (PCR): confirms diagnosis
Management
Overview
Management may include the use of doxycycline.
