Epidemiological trends in viral CNS infections in a French university hospital from 2019 to 2024, as revealed by multiplex PCR testing of cerebrospinal fluid samples

OBJECTIVES: This study aimed to characterize the epidemiology of viral infections in cerebrospinal fluid (CSF) samples over a six-year period spanning the COVID-19 pandemic, with a focus on children under 6. METHODS: In a retrospective, single-centre study at a tertiary hospital, 5294 CSF samples were analyzed between January 2019 and December 2024. Of the 4,673 deduplicated samples, 234 (5.1%) were positive for at least one virus. 111 (47.4%) of the 234 came from children under the age of six. RESULTS: Patients infected with Picornaviridae (enterovirus or parechovirus) were significantly younger than those infected with Herpesviridae (mean age: 7.7 vs 38.3 years, respectively; p<0.0001). We observed two age peaks in Picornaviridae positivity (before 6 months, and between 2 and 14 years) and one in Herpesviridae positivity (between 6 months and 2 years). As expected, the prevalence of Picornaviridae was significantly higher in summer (p=0.0002), while that of Herpesviridae did not change greatly over time. The prevalence of enterovirus infections was significantly lower during the COVID-19 pandemic period; this might reflect the influence of public health measures, changes in healthcare-seeking behaviour, and/or natural variability. CONCLUSIONS: Our epidemiological study of viral CNS infections highlighted a strongly age-dependent distribution and decreased enterovirus circulation during the COVID-19 period.