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Essentials of Diagnosis
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Exposure to sheep, goats, cattle; some laboratory-acquired infections
Acute or chronic febrile illness: headache, cough, prostration, and abdominal pain
Pneumonitis, hepatitis, or encephalopathy; less often, endocarditis, vascular infections or chronic fatigue syndrome
A common cause of culture-negative endocarditis
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General Considerations
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Q fever, a reportable and significantly underestimated disease in the United States, is caused by the gram-negative intracellular coccobacillus Coxiella burnetii
Human infection occurs via inhalation of aerosolized bacteria (in dust or droplets) from feces, urine, milk, or products of conception of infected animals
Ingestion and skin penetration are other recognized routes of transmission
There is a known occupational risk for animal handlers, slaughterhouse workers, veterinarians, laboratory workers, and other workers exposed to animal products
In the United States, over 60% of cases do not report an exposure to potentially infectious animals; drinking raw milk may be an infectious exposure
Human-to-human transmission does not seem to occur, but maternal-fetal infection can occur
Infection post-liver transplant has been reported
Chronic Q fever is now termed "persistent localized infections"
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Asymptomatic infection is common
For the remaining cases, a febrile illness develops after an incubation period of 2–3 weeks, usually accompanied by headache, relative bradycardia, prostration, and muscle pains
Clinical course may be acute, chronic (duration 6 months or longer), or relapsing
Pneumonia and granulomatous hepatitis are the predominant manifestations in the acute form
Less common manifestations include
Skin rashes (maculopapular or purpuric)
Fever of unknown origin
Myocarditis
Pericarditis
Aortic aneurysms
Aseptic meningitis
Encephalitis
Orchitis
Iliopsoas abscess
Spondylodiscitis
Tenosynovitis
Granulomatous osteomyelitis (more often seen in children)
Regional (mediastinal)
Diffuse lymphadenopathies
Culture-negative endocarditis is most common presentation in patients with persistent focalized infections
Risk factors include
Clinical manifestations of endocarditis are nonspecific with fever, night sweats, and weight loss
Sudden cardiac insufficiency, stroke, or other embolic and mycotic aneurysms can develop
Rarely, urticaria, edema, erythema nodosum, and arthralgias are reported
New infection or reactivation of Q fever can occur in pregnant women and is associated with
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Differential Diagnosis
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Elevated liver biochemical tests
Leukocytosis
A fourfold rise between acute and convalescent sera by indirect immunofluorescence is diagnostic of the infection
Real-time PCR for C burnetii DNA is helpful only in early stage of infection
Diagnostic tests using Immuno-PCR and combining PCR with ELISA improve the sensitivity and specificity during ...