Background The study was designed to examine the epidemiology of appendicitis and risk factors of perforation and appendectomy. Methods Retrospective analysis of the California Office of Statewide Health Planning and Development Patient Discharge Data was performed from 1995 to 2009. Patients with appendicitis were identified by ICD-9 diagnosis code. Population statistics from the RAND Corporation were used to calculate incidence rates. Risk factors of perforation and appendectomy were also calculated. Results A total of 608,116 patients with appendicitis (70 % non-perforated) were included. The incidence increased at an average rate of 0.5 cases/100,000 population/ year (p <0.001), with annual incidence peaking during the third quarter. Children age 10-14 had the highest rates of appendicitis (169.6 cases/100,000). The lifetime cumulative incidence rate is 9.0 %. Appendicitis is most common in whites and Hispanics and less common in African Americans and Asians. Risks of perforation include Hispanic or Asian race, young or old age, and nonprivate insurance. The adjusted odds of appendectomy increased since 1995 in patients with non-perforated appendicitis (OR 1.5, 95 % CI (1.3-1.7); p <0.001), but it decreased in patients with perforated appendicitis (OR 0.4, 95 % CI (0.4-0.5); p <0.001). Conclusions This is the largest epidemiological study of appendicitis to our knowledge in recent years. Incidence has increased over time and is higher in the summer months. Whites and Hispanics have higher rates of appendicitis, but Hispanics and Asians and patients with non-private insurance, have higher odds of perforation. Surgical management of perforated appendicitis has decreased over time. It is unknown why the incidence has increased, displays seasonality, and varies by race.
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