Table 4 Standardised incidence ratios and 95% CI of developing Crohn's disease by the time since appendectomy, stratified by cause of appendectomy.

Time since appendectomy (years)	Overall SIR (95% CI)	Appendicitis or mesenteric lymphadenitis SIR (95% CI)	Perforated appendicitis SIR (95% CI)	Non‐perforated appendicitis SIR (95% CI)	Mesenteric lymphadenitis SIR (95% CI)	Non‐inflamed appendix* SIR (95% CI)
<0.5	8.69 (7.68 to 9.84)	7.16 (6.08 to 8.44)	12.12 (8.92 to 16.46)	6.10 (4.99 to 7.46)	6.93 (3.30 to 14.53)	12.12 (10.03 to 14.63)
0.5–<1	3.16 (2.58 to 3.89)	2.85 (2.20 to 3.69)	5.99 (3.86 to 9.28)	2.11 (1.50 to 2.97)	3.78 (1.42 to 10.06)	3.89 (2.78 to 5.44)
1–4	1.86 (1.69 to 2.05)	1.66 (1.47 to 1.87)	2.38 (1.85 to 3.05)	1.42 (1.22 to 1.64)	2.86 (1.99 to 4.12)	2.36 (2.02 to 2.76)
5–9	1.25 (1.12 to 1.39)	1.15 (1.01 to 1.31)	1.23 (0.88 to 1.70)	1.12 (0.96 to 1.30)	1.31 (0.86 to 2.01)	1.51 (1.25 to 1.81)
10–14	1.03 (0.91 to 1.17)	0.88 (0.75 to 1.03)	1.28 (0.90 to 1.82)	0.73 (0.59 to 0.89)	1.45 (0.97 to 2.17)	1.44 (1.17 to 1.77)
15–19	0.98 (0.84 to 1.15)	0.85 (0.69 to 1.03)	1.05 (0.65 to 1.68)	0.81 (0.64 to 1.03)	0.80 (0.43 to 1.50)	1.31 (1.02 to 1.69)
⩾20	1.09 (0.93 to 1.27)	1.01 (0.82 to 1.23)	0.84 (0.45 to 1.55)	0.96 (0.76 to 1.22)	1.48 (0.91 to 2.41)	1.25 (0.97 to 1.61)

SIR, Standardised incidence ratio.

*Non‐inflamed appendix includes appendectomy patients without appendicitis or mesenteric lymphadenitis.