RESULTS
A total of 493 124 participants were included in this study. The mean follow-up time for the appendectomy group was 7.05 (±3.91) years, and that for the comparison group was 7.17 (±3.88) years. The distribution of demographics and comorbidities between appendectomy patients and controls is presented in Table 1. The proportions of age groups and gender were not significantly different between the 2 groups. Most of the study population was in the age group of 20–34 years (38.5%) and most participants were male (51.4%). The mean age of the case group was 43.3 (±16.7) years and that of the control group was 43.1 (16.9) years. The proportion of patients with comorbidities was significantly higher in the appendectomy group than in the control group.
Table 2 shows the incidence and HRs of IBDs. The incidence rate of IBDs in the case group was 14.7 per 10 000 person years, and that in the comparison group was 4.92 per 10 000 person years. The IBD risk in patients with appendectomy was 2.78-fold higher than (95% confidence interval [CI] = 2.17-3.55) that in people without appendectomy. Appendectomy increases UC risk by 2.23 times (95% CI = 1.59-3.12). The adjusted HR of CD for appendectomy patients compared with controls was 3.48 (95% CI = 2.42-4.99). Appendectomy increased IBD risk regardless of gender or age groups. The adjusted HR of IBDs was higher in patients with comorbidities (adjusted HR = 3.12, 95% CI = 2.34-4.17) than in participants without comorbidities (adjusted HR = 1.75, 95% CI = 1.11-2.77).
The incident rates and HRs of IBDs stratified based on the follow-up period are presented in Table 3. The adjusted HRs of IBDs for patients with appendectomy relative to controls were 3.99 (95% CI = 2.69-5.91), 2.67 (95% CI = 1.64-4.35), and 1.74 (95% CI = 1.14-2.66) in people with a follow-up time of <3, 3–6, and >6 years, respectively. For UC and CD, the highest adjusted HR was observed in patients with a follow-up time of <3 years.
Table 4 presents the incidence and risk of UC and CD for the appendectomy cohort without appendicitis and with appendicitis compared with those for the nonappendectomy cohort. The incidence and risk of UC (13.4 vs 2.77 per 10 000 person years, adjusted HR = 3.19, 95% CI = 1.86-5.50) and CD (14.8 vs 2.15 per 10 000 person years, adjusted HR = 6.13, 95% CI = 3.54-10.6) were substantially higher in the appendectomy cohort without appendicitis than in the nonappendectomy cohort. However, the incidence and risk of UC (6.08 vs 2.77 per 10 000 person years, adjusted HR = 2.11, 95% CI = 1.49-2.98) and CD (7.39 vs 2.15 per 10 000 person years, adjusted HR = 3.24, 95% CI = 2.24-4.68) were higher in the appendectomy cohort with appendicitis than in the nonappendectomy cohort.
Table 5 lists the incidence and risk of UC and CD among patients of various ages with appendectomy compared with the corresponding controls. The incidence and risk of UC and CD were significantly higher in the appendectomy cohort irrespective of when appendectomy was conducted than in the corresponding controls.
Figure 1 shows that the cumulative incidence of IBDs in patients with appendectomy was significantly higher than that of the comparison group (P value < .001).