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Key Features

Essentials of Diagnosis

  • 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

General Considerations

  • 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"

Clinical Findings

  • 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

      • Immunocompromised state

      • Preexisting valvular conditions

      • Male sex

      • Age above 40 years

      • Valvular prosthesis (mechanical or bioprosthesis)

    • 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

    • Spontaneous abortions

    • Intrauterine growth retardation

    • Intrauterine fetal death

    • Premature delivery

    • Oligohydramnios (when infection occurs during first trimester)

Differential Diagnosis

  • Viral, mycoplasmal, and bacterial pneumonias

  • Viral hepatitis

  • Brucellosis

  • Legionnaire disease

  • Murine or scrub typhus

  • Kawasaki disease

  • Tuberculosis

  • Psittacosis


Laboratory Findings

  • 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 ...

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