A 48 year-old woman presents to the emergency department with urinary frequency, fever, nausea and vomiting. She went to an urgent care center 5 days ago and was prescribed ciprofloxacin for urinary tract infection. However, she reports, ‘it didn’t do anything for me’. The left flank pain got worse and now she is passing bubbly, very foul smelling urine. Her temperature is 102 °F, heart rate is 108 beats/min, blood pressure is 168/98 mm Hg, respirations are 19 breaths/min, and oxygen saturation is 97% on room air. On physical examination, left costovertebral angle tenderness is present. You ordered some tests and the results are given below. A plain renal radiograph showed extensive bubbles in the parenchyma with a gas crescent surrounding the left kidney within the perinephric space. A CT of the abdomen and pelvis demonstrates gas in the left renal parenchyma. Which of the following is the most important risk factor associated with this disorder?
