Q fever overview

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ahmed Younes M.B.B.CH [2]

Q fever Microchapters
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Patient Information
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Q fever from other Diseases
Epidemiology and Demographics
Risk Factors
Screening
Natural History, Complications, and Prognosis
Diagnosis
History and Symptoms
Physical Examination
Laboratory Findings
Chest X Ray
CT
MRI
Other Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Surgery
Primary prevention
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Overview

Q fever is caused by infection with Coxiella burnetii. This organism is uncommon but may be found in cattle, sheep, goats and other domestic mammals, including cats and dogs. The infection results from inhalation of contaminated particles in the air, and from contact with the vaginal mucus, milk, feces, urine, or semen of infected animals. The incubation time is 9-40 days. It is considered to be possibly the most infectious disease in the world, as a human being can be infected by a single bacterium.

Historical prespective

The disease was first described by Edward Holbrook Derrick in Australia and the pathogen was first described in 1937 by Frank Macfarlane Burnet.

Classification

According to the onset of symptoms, Q fever can be classified as acute or chronic.

Pathophysiology

Q fever is a disease caused by C. burnetii, an intracellular, gram-negative proteobacterium. The disease can have a wide range of clinical presentations and affect many organ systems due to the unique virulence factors of the organism.

Causes

Q fever is caused by the bacteria C. burnetii, which lives in domestic animals such as cattle, sheep, goats, birds, and cats. Some wild animals and ticks also carry the bacteria. Q fever may be contracted through drinking raw (unpasteurized) milk, or after inhaling dust or droplets in the air that are contaminated with animal feces, blood, or birth products.

Differential diagnosis

Q fever must be differentiated from other diseases that cause atypical pneumonia such as Mycoplasma pneumonia and legionellosis.

Epidemiology and demographics

C. brutenii is found everywhere except Antarctica and New Zealand. The disease is slightly more prevalent in the elderly and in the male population.

Risk factors

The organism is present mainly in the secretions of cattle and sheep. Any occupation that involves contact with cattle and sheep increases the risk of contracting the disease.

Natural history, complications, and prognosis

Acute Q fever has a good prognosis even without treatment. Chronic Q fever has a less favorable prognosis.

History and symptoms

Acute Q fever presents with flu-like symptoms, pneumonia, and hepatitis. Chronic Q fever almost always presents with endocarditis and sometimes gives musculoskeletal and vascular manifestations.

Physical examination

Patients with Q fever usually appear ill. Physical examination of patients with Q fever is usually remarkable for fever, pneumonia, and hepatomegaly.

Laboratory Findings

Laboratory findings consistent with the diagnosis of Q fever include positive serology for antibodies (especially indirect immunofluorescence (IIF), positive PCR, and elevated liver enzymes.

Chest X Ray

On chest X-ray, Q fever is characterized by either signs of atypical pneumonia (hazy, nonlocalized airspace opacities) or it may show signs of typical pneumonia (lobar consolidation and occasional pleural effusions) in few patients.

CT

Chest CT scan may be helpful in the diagnosis of Q fever. Findings on CT scan suggestive of Q fever include scattered consolidation and opacities or lobar consolidation in one specific lobe.

MRI

There are no additional MRI findings associated with Q fever. Chest X-ray and CT are usually sufficient to diagnose Q fever.

Other imaging findings

There are no other specific imaging findings for Q fever.

Other diagnostic studies

There are no additional diagnostic findings for Q fever.

Medical Therapy

The mainstay of therapy for Q fever is doxycycline. The chronic form is more difficult to treat and can require up to two years of treatment with doxycycline and hydroxychloroquine. Q fever in pregnancy is especially difficult to treat because doxycycline is contraindicated in pregnancy and so preferred treatment is trimethoprim/sulfamethoxazole.

Surgery

Surgical intervention is not recommended for the management of Q fever.

Primary prevention

Effective measures for the primary prevention of Q fever include educating the public on sources of infection, appropriate disposal of the placenta, birth products, fetal membranes, and aborted fetuses at facilities housing sheep and goats and restricting access to barns and laboratories used in housing potentially infected animals.

Secondary prevention

There are no secondary preventive measures available for Q fever.