UC Irvine

BACKGROUND: As more patients with appendicitis are treated with antibiotics, factors associated with recurrence may help inform individualized prognostication and decision-making. METHODS: This cohort study, using data from the Comparison of Outcomes of Antibiotic Drugs and Appendectomy trial, examined patients treated with antibiotics who did not undergo appendicectomy in the first 30 days. Patients who had appendicectomy between 30 days and 1 year were compared with those who did not. Marginalized logistic regression models were used to calculate adjusted risk differences (RDs) to estimate the association between baseline patient factors and the risk of undergoing an appendicectomy between 30 days and 1 year. RESULTS: Of 601 patients treated with antibiotics who did not undergo appendicectomy within 30 days (mean age 38.0 years; 217 women (36.1 per cent)), 144 had an appendicectomy and 56 were lost to follow-up between 30 days and 1 year. The estimated rate of appendicectomy between 30 days and 1 year was 28.6 (95 per cent c.i. 25.0 to 32.8) per cent. After adjustment for other factors, nausea, vomiting, or anorexia at baseline presentation was associated with an increased rate of appendicectomy between 30 days and 1 year (adjusted RD 17.52, 95 per cent c.i. 8.64 to 26.40). The presence of an appendicolith (adjusted RD 3.64, -6.08 to 13.36), or an abscess, perforation, or fat stranding on initial imaging (adjusted RD -7.23, -17.41 to 2.95) was not strongly associated with appendicectomy between 30 days and 1 year. CONCLUSION: Most factors commonly associated with appendicitis severity were not strongly associated with an increased risk of undergoing appendicectomy in the longer term after treatment with antibiotics.