An older adult presents with left-side "rib pain," fever, and papular eruptions on the chest. What is the most likely cause of the patient's symptoms?

The symptoms presented—a combination of left-side rib pain, fever, and papular eruptions on the chest—strongly suggest herpes zoster, also known as shingles. This viral infection arises from the reactivation of the varicella-zoster virus, which causes chickenpox.

In older adults, the incidence of herpes zoster is higher due to waning immunity. The rib pain aligns with the dermatomal distribution of the zoster rash, often described as localized pain that can precede the appearance of the rash by a few days. The papular eruptions on the chest indicate the vesicular rash characteristic of herpes zoster, which typically appears in a dermatomal pattern and is often painful.

Fever may accompany the onset of shingles as the body mounts an immune response to the reactivated virus. The combination of these symptoms makes herpes zoster the most likely cause of this patient's presentation, contrasting with other options such as eczema, which generally presents with pruritic, eczematous lesions without the characteristic dermatomal pain and systemic symptoms. Intertrigo is typically associated with inflammation of skin folds, and actinic keratosis involves premalignant skin lesions usually caused by sun exposure, neither of which align with