A patient presents with a rash six days after returning from a camping and hiking trip in the woods. The rash is macular and started on the ankles and then spread to the rest of the lower extremities, including the soles. Which is the most likely diagnosis?

• A. Rocky Mountain spotted fever
• B. Typhoid fever
• C. Lyme disease
• D. Q fever

Answer: (A)

Rickettsial illness transmitted by ticks classically presents after outdoor exposure with a fever and a macular rash that begins on the extremities and moves inward. The pattern described—rash starting on the ankles and spreading up the legs, with involvement of the soles—fits Rocky Mountain spotted fever well. The incubation after a camping trip in the woods is in the typical range, and the rash often starts on wrists or ankles and can extend to the trunk and to the palms and soles as it progresses. This distribution helps distinguish it from other illnesses.

Lyme disease usually starts with an erythema migrans at the tick bite site, a localized expanding rash rather than a rash that begins at the ankles and spreads widely, and it doesn’t characteristically involve the soles. Typhoid fever features rose spots on the abdomen or trunk rather than a spreading rash starting on the legs. Q fever often presents with fever and flu-like symptoms and does not have the classic widespread rash pattern seen here.

Because RMSF can be serious, prompt treatment with doxycycline is important if suspicion is high, even before confirmatory tests.