A patient presents with a rash and painful knee joints after a hiking trip. What condition should be suspected?

The symptom profile of a rash along with painful knee joints following a hiking trip strongly suggests Lyme disease. This condition is caused by the Borrelia burgdorferi bacteria, which is transmitted to humans through the bite of infected black-legged ticks (often referred to as deer ticks).

The hallmark sign of Lyme disease is often a characteristic rash known as erythema migrans, which may appear as a "bull's-eye" pattern around the bite site. Additionally, joint pain, especially in the knees, is a common manifestation that can occur weeks to months after the initial infection. Given the context of the patient's recent outdoor activity, the exposure to potential tick bites heightens the suspicion for Lyme disease.

While other conditions may also cause rashes and joint pain, they do not have the specific connection to hiking and tick exposure as Lyme disease. For instance, tetanus does not typically present with a rash or joint pain in this context, and allergic reactions usually have a more immediate onset following exposure to an allergen but do not feature joint inflammation. Rocky Mountain spotted fever, another tick-borne illness, includes symptoms of fever and rash but is typically accompanied by more severe systemic effects and specific rash characteristics that are less common in Lyme disease. Thus,