A 65-year-old man presents with fever and a maculopapular rash after a camping trip. What is the most likely diagnosis?

The presentation of fever and a maculopapular rash following a camping trip suggests an infectious disease often associated with tick bites, guiding toward specific diagnoses prevalent in outdoor environments. Rocky Mountain spotted fever, caused by the Rickettsia rickettsii bacteria and transmitted through tick bites, typically presents with symptoms like fever, rash, and a history of exposure to areas where ticks are prevalent, such as during camping trips.

The rash associated with Rocky Mountain spotted fever often starts as maculopapular but may progress to petechial, making it distinctive. Given the timeline of symptom onset after outdoor exposure and the classic symptoms, the likelihood of contracting Rocky Mountain spotted fever is significant.

In contrast, while Lyme disease could also be a consideration, it typically presents with erythema migrans (a characteristic "bull's-eye" rash) rather than a maculopapular rash. Furthermore, Lyme disease's initial presentation often includes localized symptoms around the tick bite site, which may not explain the systemic febrile condition seen here.

Cellulitis would generally manifest with localized pain, swelling, and erythema instead of a maculopapular rash, while syphilis usually presents with different types of rashes and typically occurs