Rocky Mountain Spotted Fever

Key Features

• Caused by Rickettsia rickettsii, a parasite of ticks, transmitted by tick bites

• Most cases occur in only five states: North Carolina, South Carolina, Tennessee, Oklahoma, and Arkansas

• Most cases occur in late spring and summer

• Typical incubation period is 2–14 days (median, 7 days)

• Mortality rate is over 70% in untreated patients

Clinical Findings

• Initial symptoms include fevers, chills, headache, nausea and vomiting

• Cough and pneumonitis often occur early in the disease

• In more severe cases, delirium, lethargy, seizures, stupor, and coma may also appear

• Rash (not always found) begins as a faint macule that progresses to large maculopapules and often petechiae

• Rash begins on the wrists and ankles, characteristically involves palms and soles, and spreads to arms, legs, and trunk

• Splenomegaly, hepatomegaly, jaundice, myocarditis (which may mimic an acute coronary syndrome), adrenal hemorrhage, polyarticular arthritis, or uremia are occasionally present

• About 3–5% of recognized cases in the United States are fatal

Diagnosis

• Thrombocytopenia

• Hyponatremia

• Hepatitis

• CSF low glucose

• Immunohistologic staining for R rickettsii in skin biopsy specimens and serologic testing are the keys to a definitive diagnosis

Treatment

• Doxycycline (100 mg orally twice daily for 4–10 days) or chloramphenicol (50–100 mg/kg/day in four divided doses, orally or intravenously for 4–10 days) are usually highly effective

• Prevention: protective clothing and avoiding tick bites