# Changing Clinical Spectrum of Invasive Meningococcal Disease in France (2014–2025): Impact of Age and Meningococcal Lineage on Atypical Presentations

## TL;DR

This study shows that invasive meningococcal disease in France has changed over time, with more cases presenting in atypical ways, influenced by age and bacterial lineage.

## Contribution

The study identifies age and meningococcal lineage as key factors shaping the clinical spectrum of invasive meningococcal disease in France.

## Key findings

- Atypical presentations like bacteraemic pneumonia and abdominal forms are increasingly common in invasive meningococcal disease.
- Abdominal presentations are strongly associated with serogroups W and Y and clonal complex cc11, and are linked to higher early mortality.
- Older age and specific meningococcal lineages are linked to distinct clinical manifestations of invasive meningococcal disease.

## Abstract

Invasive meningococcal disease (IMD) is classically associated with meningitis and septic shock, but an increasing proportion of cases present with atypical, extra-meningeal manifestations. Following the COVID-19 pandemic, major epidemiological shifts have occurred in France, including a rebound in IMD incidence and changes in circulating serogroups and clonal complexes. We conducted a nationwide retrospective study including all laboratory-confirmed IMD cases analysed by the French National Reference Centre between July 2014 and June 2025. Clinical presentations were coded as non-exclusive entities. Associations with age, serogroup, clonal complex, antimicrobial susceptibility and early mortality (≤72 h) were assessed using descriptive analyses and multivariable logistic regression models. Among 4328 IMD cases, sepsis/shock (61.1%) and meningeal involvement (54.9%) predominated, while atypical forms were frequent, including bacteraemic pneumonia (7.7%), abdominal presentations (8.0%) and arthritis (6.0%). Bacteraemic pneumonia was strongly associated with older age and serogroups W and Y, whereas abdominal forms predominated in adolescents and young adults and were independently associated with serogroups W and Y and clonal complex (cc) cc11. Abdominal presentations were independently associated with early mortality (adjusted odds ratio [aOR] 2.40) but not meningococcal pneumonia. Abdominal presentations were associated with serogroup W (aOR 2.27; 95% CI 1.35–3.83) and serogroup Y (aOR 2.92; 95% CI 1.79–4.75) and with cc11 (aOR 1.77; 95% CI 1.07–2.94). In contrast, cc23 was associated with lower odds of abdominal involvement (aOR 0.42; 95% CI 0.25–0.70). Overall, atypical presentations now represent a substantial proportion of IMD in France and are strongly shaped by age and meningococcal lineage. These findings highlight diagnostic challenges, prognostic heterogeneity and the need for continued integrated clinical, microbiological and genomic surveillance in the context of evolving vaccination strategies.