Acute pyelonephritis Quiz: Ace Your Exams

An 87-year-old woman is brought to the emergency department from a nearby skilled nursing facility with confusion and vomiting for the past day. According to the nursing staff, the patient was in her usual state of health before the last 24 hours, during which she was complaining of nausea. She is normally alert and oriented to person, place and time. She has a past medical history of diabetes and hypertension, and she was recently discharged from the hospital after having an obstructed kidney stone removed and a postoperative course complicated by recurrent urinary retention. Her temperature is 38°C (100.4°F), pulse is 107/min, respirations are 22/min, blood pressure is 121/64 mmHg, and oxygen saturation is 96% on room air. She is oriented to person but not to place or time. Physical examination shows tenderness to palpation over her left flank. A Foley catheter is in place and draining dark brown urine. Which of the following is the strongest risk factor for this patient’s current clinical condition?