Q fever (Coxiella burnetii infection)
Q fever, caused by inhalation of Coxiella burnetii aerosols from infected livestock, most often produces a self-limited febrile illness with atypical pneumonia or hepatitis, but it is a major cause of culture-negative endocarditis when infection becomes chronic. Acute disease is treated with doxycycline for 2 weeks; endocarditis requires combination therapy for more than 18 months.
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What this article covers
- Overview
Zoonotic intracellular bacterial infection acquired by inhalation: Q fever is caused by Coxiella burnetii, acquired through inhalation of contaminated aerosol particles of dust, earth, or feces, or…
- Epidemiology
Livestock exposure is the dominant epidemiologic link: cattle and sheep are the most common sources, with goats also implicated; assisting in the birthing of these animals (exposure to amniotic fluid…
- Risk factors
Direct contact with birth products of infected livestock (cattle, sheep, goats): the single strongest risk factor, given the high bacterial concentration in amniotic fluid and placental tissue.
- Pathophysiology
Inhalational entry into the respiratory tract: aerosolized C burnetii organisms are inhaled and infect alveolar macrophages, from which the organism disseminates hematogenously.
- Clinical features
Fever as the dominant, often isolated, presenting feature: an acute self-limited febrile illness is the most common presentation, frequently with an atypical pneumonia picture (nonproductive cough…
- Differential diagnosis
Brucellosis: overlapping zoonotic exposure and undulant fever pattern with hepatosplenomegaly; discriminated by blood or bone marrow culture growing Brucella species and by a history of unpasteurized…
- Diagnosis
The diagnosis is established by serology, not culture, because C burnetii is fastidious and rarely recovered from standard blood cultures: acute infection is confirmed by a phase II antibody…
- Management
For acute Q fever pneumonitis or hepatitis, start doxycycline 100 mg PO or IV twice daily for 14 days, the treatment of choice for this presentation.
- Complications
Culture-negative infective endocarditis: the most serious chronic complication, with risk of valve destruction, heart failure, and embolic events if untreated or under-treated.
- Prognosis
Acute Q fever is usually self-limited, with most patients recovering fully, particularly with prompt doxycycline therapy.
- Prevention
Avoid direct contact with birth products of livestock, particularly assisting unprotected in the birthing of cattle, sheep, or goats, which carries the highest bacterial burden and transmission risk.
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Related articles
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Brucellosis is a zoonotic infection from unpasteurized dairy, undercooked meat, or animal contact causing undulant fever, hepatosplenomegaly, arthralgia, and depression, diagnosed by extended-incubation blood or marrow culture and serum agglutination titer, and treated with doxycycline plus rifampin or gentamicin for six weeks.
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