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Key Features

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Essentials of Diagnosis
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  • Residing or travel in endemic area when ticks are active

  • Fever, rash (palms and soles), gastrointestinal symptoms, headache

  • Tick bite reported (50%)

  • Thrombocytopenia, hyponatremia

  • Definitive diagnosis by specific serology

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General Considerations
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  • Caused by Rickettsia rickettsii

  • Most severe rickettsial infection

  • Occurs predominantly along the eastern seaboard; in the southeastern states; and in Arkansas, Missouri, and Oklahoma

  • About 2000 cases occur in the United States each year

  • Most cases occur in children exposed in rural areas from April to September

  • Infection can be acquired from dog ticks

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Clinical Findings

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Symptoms and Signs
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  • Incubation period is 3–12 days (mean, 7 days)

  • High fever (> 40°C, often hectic), usually of abrupt onset

  • Myalgia

  • Severe and persistent headache (retro-orbital), photophobia

  • Vomiting, abdominal pain, and diarrhea

  • Rash

    • Occurs in more than 95% of patients

    • Appears 2–6 days after fever onset

    • Begins as macules and papules involving palms, soles, and extremities

    • Becomes petechial and spreads centrally from the extremities

    • Reflects infection of endothelial cells, which also causes vascular leak and resulting edema, hypovolemia, and hypotension

  • Conjunctivitis, splenomegaly, pneumonitis, meningismus, and confusion may occur

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Differential Diagnosis
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  • Meningococcemia

  • Measles

  • Meningococcal meningitis

  • Staphylococcal sepsis

  • Epstein-Barr virus infection

  • Enteroviral infection

  • Leptospirosis

  • Colorado tick fever

  • Scarlet fever

  • Endemic typhus (murine typhus)

  • Kawasaki disease

  • Ehrlichiosis

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Diagnosis

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Laboratory Findings
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  • Thrombocytopenia

  • Hyponatremia

  • Early mild leukopenia

  • Proteinuria

  • Mildly abnormal liver function tests

  • Hypoalbuminemia

  • Hematuria

  • CSF pleocytosis

  • Serologic diagnosis

    • Achieved with indirect fluorescent or latex agglutination antibody methods

    • Informative only 7–10 days after onset of the illness

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Diagnostic Procedure
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  • Skin biopsy with specific fluorescent staining is a specific and moderately sensitive method available during the first week of the illness

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Treatment

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  • Must be started early, most often on the basis of a high clinical suspicion prior to rash onset in endemic areas

  • Doxycycline

    • Treatment of choice for children, regardless of age

    • Dosing: 2 mg/kg every 12 hours (IV or PO; maximum 100 mg per dose) for 2 or 3 days after the temperature has returned to normal for a full day

    • Duration: minimum of 10 days is recommended

  • Tick attachment lasting 6 hours or longer is needed, so removing tick within that timeframe can be preventive

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Outcome

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Prognosis
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  • Complications and death result from severe vasculitis, especially in the brain, heart, and lungs

  • Mortality rate is 5–7%

  • Persistent neurologic deficits occur in 10–15% of children who recover

  • Delay in therapy is an important determinant of sequelae and mortality

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References

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Lin  L, Decker  CF: Rocky Mountain spotted fever. Dis Mo 2012;58(6):361–369
[PubMed: 22608123] .
CrossRef
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Woods  CR: Rocky mountain spotted fever in children. ...

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