Temporal Trends and Serogroup Distribution of Invasive Meningococcal Disease in Istanbul, Türkiye, 2021-2025.

Objectives

This population-based cohort study evaluates temporal trends, clinical characteristics, and serogroup distribution of Invasive Meningococcal Disease (IMD) in Istanbul, Türkiye, from 2021 to 2025.

Methods

Poisson regression models were used to evaluate changes in incidence rates across age groups over the years, calculating Incidence Rate Ratios (IRRs) and 95% confidence intervals.

Results

A total of 77 confirmed IMD cases were identified. The median age was 7 years (1-17), and 54.5% of patients were male. Serogroup B was the predominant strain, and meningitis was the most frequent clinical presentation. The IMD incidence increased significantly from 0.04 per 100000 population in 2021 to 0.17 per 100000 population in 2025, with an IRR of 1.45 (95% CI: 1.22-1.73; p<0.001). Children aged 0-4 years experienced the highest IMD burden, with incidence increasing significantly from 0.29 per 100000 in 2021 to 1.06 per 100000 in 2025 (IRR=1.35, 95% CI: 1.05-1.74; p=0.019). Intensive care admission was required in 42.9% of patients, while the overall case-fatality rate was 6.5%, increasing to 9.1% among children aged 0-4 years.

Conclusion

Serogroup B predominance and severe 0-4 age vulnerability highlight the importance of sustained surveillance.