Changes in the epidemiology of acute mastoiditis according to the implementation of pneumococcal vaccination in a Spanish population

Purpose: To describe the epidemiology of acute mastoiditis over a 20-year period (2000-2019) in the pediatric population attended in our institution, and to evaluate changes in the etiology according to the implementation of pneumococcal conjugate vaccines (PCV). Methods: : Retrospective, observational study including children < 16 years diagnosed with acute mastoiditis between January 2000 and December 2019 at a tertiary hospital in Madrid (Spain). The study was grouped into four 5-year periods (2000-2004, 2005-2009, 2010-2014, and 2015-2019) and the percentage change (PC) in the incidence rate and in the prevalence of each microorganism isolated were estimated to characterize trends, with log-transformed data models. Result: 219 episodes from 209 patients were included. The incidence rate of AM remained stable during the study period, with an average of 2.2 cases/10,000 emergency department visits/year. There was a significant decrease in the prevalence of S. pneumoniae (PC: -22.4% [95% CI: −34.9, -7.4]; p=0.025), from 19% in the pre-PCV period (2000-2005) to 9% in the last period. Serotypes contained in the PCV13 significantly decrease from 92% in the pre-PCV13V period to 33% in the post-PCV13V period (p=0.022). S. pyogenes was the main microorganism isolated in the last study period, showing a significant increase in its prevalence from 5% in the third to 19% in the last period (p=0.046). Conclusions: : Although the incidence of AM in children remained stable in our study, the prevalence of S. pneumoniae significantly decreased in the post-PCV era, with S. pyogenes becoming the main microorganism isolated after the implementation of PCV13.