Incidence of fistula-in-ano complicating anorectal sepsis: a prospective study.

The incidence of fistula-in-ano following anorectal abscesses was studied prospectively in 50 consecutive patients. A total of 13 patients (26 per cent; 95 per cent confidence limits: 14-40) had a fistula diagnosed either in the acute phase or during follow-up within 6 months. Half of the fistulas diagnosed at follow-up were unrecognized by the patients and no fistulas developed in patients where culture from the abscess only revealed skin-derived bacterias. X-ray examination was of no value in the diagnosis of anal fistula.