We use the term acute complicated urinary tract infection (UTI) to refer to an acute UTI with any features that suggest that the infection extends beyond the bladder . These include fever (eg, >99.9°F/37.7°C), other signs or symptoms of systemic illness (including chills, rigors, or altered mental status), flank pain, and costovertebral angle tenderness. By this definition, pyelonephritis is a complicated UTI, regardless of patient characteristics