COVID-19 and Appendicitis: Insights from a Retrospective Study

To identify whether a relationship exists between COVID-19 and appendicitis and compare the incidence of appendicitis during three pandemic years to the year prior to the pandemic, we conducted two observational retrospective studies: a propensity score-matched (PSM) cohort and a repeated monthly cross-sectional study. We used data from the Military Health System (MHS) Data Repository, which contains data about healthcare provided to active-duty service members, retirees, and their dependents. For the PSM cohort of 753,138 individuals, patients with COVID-19 between July 2020 and June 2021 from the MHS were matched to two similar people without COVID-19. Survival analysis using a conditional Cox proportional hazards model explored these relationships. For the cross-sectional study we used a separate, unmatched MHS cohort of 10,402,021 individuals. Poisson regression generated incident rate ratios (IRRs) of any appendicitis or complicated appendicitis by year, comparing three pandemic years to one pre-pandemic year. COVID-19 was associated with appendicitis or appendectomy within the first year of infection (hazard ratio: 1.13, 95% confidence interval: 1.02–1.26). The IRRs for both any appendicitis and complicated appendicitis were significantly less than one when comparing individual pandemic years to the pre-pandemic year. COVID-19 is associated with appendicitis. Rates of any appendicitis and complicated appendicitis were lower in each individual pandemic year.