Trends in Streptococcus pneumoniae serotypes and antimicrobial resistance in Italy (2007–2023): A mixed-effects model analysis of invasive pneumococcal disease

Introduction Invasive pneumococcal disease (IPD) remains a significant public health concern despite the widespread implementation of pneumococcal conjugate vaccines (PCVs). Shifts in serotype distribution and antimicrobial resistance (AMR) patterns, particularly in the post-PCV13 era, necessitate ongoing surveillance to inform vaccine and treatment policies. Methods We conducted a retrospective analysis of laboratory-confirmed IPD cases reported in the Veneto Region of north-eastern Italy between 2007 and 2023. Data were obtained from regional surveillance systems and included serotype, clinical presentation, demographics, and antimicrobial susceptibility. Trends in IPD incidence were modelled using negative binomial generalised linear mixed models (GLMM). Serotype distribution and AMR patterns were examined over time and in relation to age, sex, and clinical syndrome. Results A total of 59 pneumococcal serotypes were identified. Serotype 3 was most frequent, followed by 8 and 19 A. Significant increases were observed for serotype 8, while vaccine-included serotypes (e.g., 6 A, 23 F, 7 F) declined. AMR remained stable overall, with erythromycin and clindamycin resistance observed in 17.3 % and 13.2 % of isolates, respectively. Resistance was concentrated in serotypes 14, 15 A, and 19 A. Serotype 8 showed high prevalence but low resistance rates. The overall IPD incidence remained stable; however, a modest upward trend was observed in pre-COVID19 pandemic years. Conclusion Our findings highlight the evolving pneumococcal landscape in the post-PCV13 era, with emerging serotypes contributing significantly to IPD burden. The observed serotype-specific AMR patterns underscore the importance of integrated surveillance to support regionally tailored immunisation strategies and empirical therapy choices. Expanded-valency vaccines may offer broader protection against emerging serotypes.