Prevalence of anal fistula in the United Kingdom

Table 1 Overall prevalence of anal fistula with and without Crohn’s disease

	2014	2015	2016	2017
Prevalence of AF, n	1143	938	688	579
Prevalence of AF, n/10000 patients	2.34	2.22	1.93	1.82
Standardization to
UK (95%CI)	2.31 (2.18-2.44)	2.19 (2.05-2.33)	1.89 (1.75-2.03)	1.80 (1.65-1.94)
EU (95%CI)	2.36 (2.22-2.50)	2.23 (2.08-2.37)	1.94 (1.79-2.08)	1.83 (1.68-1.98)

AF: Anal fistula; n: Number; CI: Confidence interval; UK: United Kingdom; EU: European Union.

Table 2 Prevalence of anal fistula without Crohn’s disease

		2014	2015	2016	2017
Prevalence of AF, n		891	726	514	437
Prevalence of AF, n/10000 patients		1.83	1.72	1.44	1.38
Gender	Female, n (%)	365 (43.7)	288 (44.6)	197 (44.4)	180 (44.9)
Age	0-19, n (%)	53 (5.9)	29 (4.0)	24 (4.7)	21 (4.8)
	20-39, n (%)	314 (35.2)	249 (34.3)	162 (31.5)	137 (31.4)
	40-59, n (%)	344 (38.6)	320 (44.1)	230 (39.5)	197 (45.1)
	60-79, n (%)	147 (16.5)	112 (15.4)	112 (21.8)	70 (16.0)
	80+, n (%)	33 (3.7)	16 (2.2)	13 (2.5)	12 (2.7)
Standardization to
	UK (95%CI)	1.80 (1.68-1.92)	1.69 (1.57-1.81)	1.41 (1.29-1.53)	1.35 (1.23-1.48)
	EU (95%CI)	1.84 (1.72-1.97)	1.73 (1.60-1.85)	1.45 (1.32-1.58)	1.39 (1.26-1.52)
Direct AF Read codes1
Prevalence of Direct AF, n		586	466	347	265
Prevalence of Direct AF, n/10000 patients		1.20	1.10	0.97	0.84
Standardization to
	UK (95%CI)	1.18 (1.09-1.28)	1.09 (0.99-1.19)	0.96 (0.86-1.06)	0.83 (0.73-0.92)
	EU (95%CI)	1.21 (1.11-1.31)	1.11 (1.01-1.21)	0.98 (0.87-1.08)	0.84 (0.74-0.94)
Most commonly used Read codes:
Anal fissure and fistula, n		360	245	186	139
Fistula-in-ano, n		250	224	167	141
Indirect AF Read codes2
Prevalence of Indirect AF, n		391	324	214	199
Prevalence of Indirect AF, n/10000 patients		0.80	0.77	0.60	0.63
Standardization to
	UK (95%CI)	0.79 (0.71-0.87)	0.75 (0.67-0.83)	0.60 (0.58-0.50)	0.61 (0.52-0.69)
	EU (95%CI)	0.81 (0.73-0.89)	0.77 (0.69-0.86)	0.61 (0.53-0.69)	0.63 (0.54-0.72)
Most commonly used Read codes:
Anal fistula operations, n		135	98	65	69
Laying open of anal fistula NEC, n		106	87	59	41
Excision of fistula in ano, n		94	74	61	55

AF: Anal fistula; n: Number; CI: Confidence interval; UK: United Kingdom; EU: European Union; NEC: Not elsewhere classified;

¹Direct codes: Read codes directly identifying anal fistula (e.g. anal fissure and fistula, and fistula-in-ano);

²Indirect codes: Read codes identifying procedures or surgeries related specific to anal fistulas (e.g., excision of fistula in ano, and anal fistula operations); One patient can have multiple Direct and Indirect anal fistula codes.

Table 3 Prevalence of anal fistula with Crohn’s disease

		2014	2015	2016	2017
Prevalence of AF, n		252	212	174	142
Prevalence of AF, n/10000 patients		0.52	0.50	0.49	0.45
Gender	Female, n (%)	66 (43.3)	53 (42.4)	51 (46.8)	42 (43.8)
Age	0-19, n (%)	###	###	###	###
	20-39, n (%)	115 (45.6)	96 (45.3)	75 (43.4)	79 (55.6)
	40-59, n (%)	89 (35.3)	81 (38.2)	73 (42.2)	45 (31.7)
	60-79, n (%)	32 (12.7)	23 (10.8)	16 (9.2)	13 (9.2)
	80+, n (%)	###	###	###	###
Standardization to
	UK (95%CI)	0.51 (0.45-0.57)	0.50 (0.43-0.56)	0.48 (0.41-0.55)	0.44 (0.37-0.52)
	EU (95%CI)	0.52 (0.45-0.58)	0.50 (0.43-0.57)	0.48 (0.41-0.56)	0.44 (0.37-0.51)
Direct AF Read codes1
Prevalence of Direct AF, n		149	125	109	96
Prevalence of Direct AF, n/10000 patients		1.31	1.30	0.31	0.30
Standardization to
	UK (95%CI)	0.30 (0.25-0.35)	0.29 (0.24-0.34)	0.30 (0.24-0.36)	0.30 (0.24-0.36)
	EU (95%CI)	0.30 (0.26-0.35)	0.29 (0.24-0.35)	0.30 (0.25-0.36)	0.30 (0.24-0.36)
Indirect AF Read codes2
Prevalence of Indirect AF, n		147	125	102	70
Prevalence of Indirect AF, n/10000 patients		0.30	0.30	0.29	0.22
Standardization to
	UK (95%CI)	0.30 (0.25-0.34)	0.29 (0.24-0.34)	0.28 (0.23-0.34)	0.22 (0.17-0.27)
	EU (95% CI)	0.30 (0.25-0.35)	0.29 (0.24-0.35)	0.28 (0.23-0.34)	0.22 (0.17-0.27)

AF: Anal fistula; n: Number; CI: Confidence interval; UK: United Kingdom; EU: European Union;

¹Direct codes: Read codes directly identifying anal fistula (e.g., anal fissure and fistula, and fistula-in-ano);

²Indirect codes: Read codes identifying procedures or surgeries related specific to anal fistulas (e.g., excision of fistula in ano, and anal fistula operations); One patient can have multiple Direct and Indirect anal fistula codes; ### masking due to small patient numbers (n: 1-5).

Table 4 Prevalence of comorbidities in anal fistula with and without Crohn’s disease

	2014		2015		2016		2017
	without CD	with CD	without CD	with CD	without CD	with CD	without CD	with CD
Prevalence of AF, n	891	252	726	212	514	172	437	142
Prevalence of AF with any comorbidity	148	39	124	28	96	26	82	18
per 10000 patients	0.30	0.08	0.29	0.07	0.27	0.07	0.26	0.06
per 100 AF patients	16.61	15.48	17.08	13.21	18.68	15.03	18.76	12.68
Prevalence of comorbidities per 100 AF patients1
HIV	0	###	###	###	0	###	###	###
Anal carcinoma	###	0	###	0	###	0	###	0
Radiation in the pelvic area	1.91	###	1.79	###	1.75	###	3.43	###
Diabetes mellitus type 1 or 2	8.98	5.16	8.13	5.19	10.12	5.20	8.92	4.93
Diverticulitis, colon/rectum	4.38	###	4.96	###	5.84	3.47	5.26	###
Hidradenitis suppurativa	0.90	###	1.38	###	1.95	3.47	1.60	4.23
Proctitis	1.46	4.76	2.20	3.77	1.36	4.62	1.83	###
Congenital anal fistula	0	0	###	0	0	0	0	0

AF: Anal fistula; n: Number; HIV: Human immunodeficiency virus;

¹No patients with anal tuberculosis, anal syphilis, anal gonorrhoea, anal chlamydia, lymphogranuloma venereum were detected; ### masking due to small patient numbers (n: 1-5).