B.W., a 35-year-old woman, is admitted to a 10-bed medical ward for the treatment of Streptococcus..

B.W., a 35-year-old woman, is admitted to a 10-bed medical ward for the treatment of Streptococcus pneumoniae meningitis. On arrival, she is started on ceftriaxone (Rocephin) 2 g IV every 12 hours and improves during the next few days. On day 7 of antibiotic therapy, she complained of feeling warm, with cramping abdominal pain and diarrhea. She began passing mucoid, greenish, foul-smelling watery stools, and had a temperature of 101?F. Microscopic examination of a stool sample was positive for fecal leukocytes. The physician’s assessment of B.W.’s clinical and laboratory findings is antibiotic-associated diarrhea (AAD), most likely caused by C. difficile. What are the primary risk factors for this patient’s AAD?