A 9-year-old boy has had fever, muscle aches, nausea, vomiting, and diffuse abdominal pain for the past 5 days. Two days ago, his mother noted a rash consisting of multiple 2 to 3 mm blanching, erythematous macules around his wrists and ankles that spread to his chest, back, arms, and thighs today. Choose the true statement regarding this patient:
This rash rarely involves the palms or soles.
+The classic triad of fever, rash, and tick bite occurs in more than 75% of cases.
+A history of tick bite can be elicited in 95% of cases.
+Patients younger than 20 years account for 20% of cases.
+The causative organism is an obligate intracellular bacterium.
This patient has Rocky Mountain spotted fever, an acute febrile tick-borne illness caused by Rickettsia Rickettsii. RMSF is most common in the states of the mid-eastern seaboard but has been reported in nearly every state. The female dog tick, Dermacentor variabilis, is the vector in the east; the vector in the west is the wood tick, D. andersoni. The disease is seasonal, with most cases occurring from April to September. Sixty percent of cases occur in patients younger than 20 years. The onset is usually abrupt, with high fevers, shaking chills, myalgias, abdominal pain, and a severe headache. Variations from this pattern should not dissuade one from the diagnosis and the classic triad of fever, rash, and a tick bite is apparent in less than 5% of patients. Classically, a macular rash begins on the wrists, palms, ankles, and soles 2–6 days after the onset of fever and spreads centripetally. The rash evolves to dark, nonblanching, and petechial or ecchymotic lesions. Empiric treatment with doxycycline should be initiated prior to serologic tests or skin biopsy results. The mortality rate is 8–20% for untreated patients.