Which signs and symptoms suggest pyelonephritis rather than acute simple cystitis?

Fever, chills, flank or back pain, and nausea/vomiting are key indicators of pyelonephritis, which is an infection of the kidney, as opposed to acute simple cystitis, which primarily involves the bladder. The presence of systemic symptoms such as fever and chills suggests a more serious infection that has ascended beyond the bladder. Flank or back pain is particularly indicative of kidney involvement, as this area corresponds to where the kidneys are located. Nausea and vomiting can occur due to the body's response to a more severe infection, as well as possible irritation of the gastrointestinal system from the systemic effects of the infection.

Other symptoms associated with lower urinary tract infections, such as lower abdominal pain, dysuria, and urgency to urinate, are more typical of cystitis and do not indicate kidney involvement. The same is true for symptoms like itching and frequent urination, which may arise from bladder irritation rather than kidney infection. Night sweats and confusion can occur in various infections but are less specific and not necessarily indicative of pyelonephritis compared to the classic symptoms highlighted in the correct answer.