Which of the following is a symptom of pyelonephritis?

Pyelonephritis, an infection of the kidneys, commonly presents with symptoms related to the urinary tract and the kidneys themselves. Back pain is a hallmark symptom of this condition, as inflammation and infection in the kidneys typically cause discomfort in the lower back region. The pain often appears as a dull ache in the flank area, which corresponds to the location of the kidneys.

In contrast, while nausea can occur with various illnesses, it is not as specific to pyelonephritis as back pain. Joint pain and chest pain are generally not associated with kidney infections. Joint pain may suggest other musculoskeletal issues or systemic conditions, and chest pain is typically related to cardiac or pulmonary issues rather than kidney infections. Thus, back pain directly correlates with the location and nature of the kidney infection, making it the most relevant symptom in diagnosing pyelonephritis.