Rocky Mountain Spotted Fever

Key Features

Essentials of Diagnosis

• 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

General Considerations

• 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

Clinical Findings

Symptoms and Signs

• 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

Differential Diagnosis

• 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

Diagnosis

Laboratory Findings

• 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

Diagnostic Procedure

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

Treatment

• 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

Outcome

Prognosis

• 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

References