Which bacterial pathogen is the likely cause of a rash starting on the palms and spreading to the lower arms after a camping trip?

The likely cause of a rash that starts on the palms and spreads to the lower arms after a camping trip is Rickettsia rickettsii. This bacterium is known to cause Rocky Mountain spotted fever (RMSF), which is characterized by its distinctive rash and is transmitted by tick bites. The rash typically begins on the wrists and ankles, then spreads to the palms and soles, which aligns with the symptom described in the question.

Rickettsia rickettsii poses a particular risk for individuals who engage in outdoor activities, especially in areas where infected ticks are prevalent. The characteristic palmar rash and the contextual clue of a camping trip strongly support this diagnosis, making it a key feature when identifying the pathogen responsible for these symptoms.

In comparison, other pathogens listed in the choices have different clinical presentations and are associated with distinct epidemiological patterns. While Coxiella burnetii is related to Q fever and typically doesn't present with such a rash, Ehrlichia chaffeensis is associated with human monocytic ehrlichiosis and usually presents with fever and possibly petechial rash but not characteristically on the palms. Anaplasma phagocytophilum causes human granulocytic anaplasmosis and likewise does not