Fistula-in-ano in a defined population. Incidence and epidemiological aspects.

The incidence and epidemiology of anal fistula were studied among the inhabitants of the City of Helsinki (population 510,000) during a 10-year period, 1969 to 1978. The mean incidence per 100,000 population was 8.6 for nonspecific and fistula, 12.3 for males and 5.6 for females. Of a total of 458 anal fistulae diagnosed during the period under study, the nonspecific fistulae accounted for 90.4%, the tuberculous fistulae for 0.2%, the postoperative and traumatic fistulae for 3.3% and fistulae originating in anal fissure for 3.3%. Anal fistulae associated with ulcerative colitis comprised 1.5% of the total series and fistulae associated with Crohn's disease 1.3%. At the time of diagnosis of the nonspecific anal fistulae, the mean age of the patients was 38.3 years; the male-female ratio was 1.8: 1. All the patients younger than 15 years of age were male. 35% of anorectal abscesses of nonspecific anal origin developed into a fistula. Sedentary occupations did not show any significance in anal fistula formation.