Which of the following symptoms is characteristic of Rocky Mountain spotted fever?

The distinctive rash on extremities is a key characteristic of Rocky Mountain spotted fever (RMSF), which is caused by the bacterium Rickettsia rickettsii. This rash typically begins as small, flat, pink spots (macules) that develop into petechiae, which are tiny, red or purple spots caused by bleeding under the skin. The rash often appears between the 2nd and 5th day of illness, usually starting on the wrists and ankles before moving inward to the trunk.

RMSF is known for this specific pattern of rash and its rapid progression, which is a critical factor in diagnosing the disease and differentiating it from other conditions. Recognizing the rash, especially in the context of fever and other systemic symptoms, is crucial for prompt treatment with antibiotics, as delayed treatment can lead to severe complications.