To identify patients with a diagnosis of Clostridium difficile–associated disease (CDAD) in the ambulatory care setting and determine the relationship of symptom onset and diagnosis to prior hospitalization and exposure to antimicrobials.

Single-center, retrospective study.

Medical records were reviewed for outpatients and hospitalized patients with a stool assay positive for C. difficile toxin A from January 1998 through March 2005. Patients with recurrent CDAD or residing in an extended-care facility were excluded. CDAD in patients who had been hospitalized in the 100 days prior to diagnosis was considered potentially hospital-associated.

Of the 84 patients who met the inclusion criteria, 75 (89%) received a diagnosis 1-60 days after hospital discharge (median, 12 days), and 71 (85%) received a diagnosis within 30 days after discharge. Of the 69 patients whose records contained information regarding time of symptom onset, 62 (90%) developed diarrhea within 30 days of a previous hospital discharge, including 7 patients with symptom onset prior to discharge and 9 with onset on the day of discharge. The median time from symptom onset to diagnosis was 6 days. Of 84 patients, 77 (92%) had received antimicrobials during a prior hospitalization, but 55 (65%) received antimicrobials both as inpatients and as outpatients.

If all cases of CDAD diagnosed within 100 days of hospital discharge were assumed to be hospital-associated, 71 (85%) of 84 patients with CDAD were identified within 30 days, and 75 (89%) of 84 were identified by day 60. Continued outpatient antimicrobial exposure confounds determination of whether late-onset cases are community- or hospital-associated.