The Meningitis and Encephalitis Registry of Lower Saxony, Germany (MERIN) – design and main results of circulating neurotropic pathogen surveillance, 2003 to 2023

BACKGROUND The Meningitis and Encephalitis Registry in Lower Saxony (MERIN), introduced in 2003, monitors circulating neurotropic pathogens in Lower Saxony and Bremen and offers free laboratory diagnostics for patients hospitalised with aseptic meningitis, encephalitis and polio-like symptoms. AIM We aimed to present set-up and operation of MERIN in detail and provide results of the collected data. METHODS Data (work-flow, demographics, sample materials, detected pathogens including non-polio enterovirus (NPEV) genotypes), collected between 2003 and 2023 were extracted from the MERIN database and presented descriptively. Seasonal patterns of detected pathogens were analysed using a Poisson regression model. RESULTS During 21 years of MERIN’s operation, 34,688 samples from 13,813 patients were analysed, 54.6% (7,548/13,813) of which were male. The majority of patients were children, with 58.8% (8,127/13,813) under the age of 10 years. Twenty different pathogens were identified; NPEV infections constituted 56.9% (2,372/4,172) of all diagnoses and were found in 17.2% of patients (2,372/13,813). Borrelia burgdorferi sensu lato , adenovirus and varicella-zoster virus were identified in 7.3% (1,004/13,813), 2.1% (286/13,813) and 1.4% (190/13,813) of patients, respectively. Most frequently occurring NPEV genotypes were echovirus 30 (n = 437), echovirus 6 (n = 223) and coxsackie B virus (n = 103). Polioviruses were not detected. Increased numbers of patients and detected pathogens during summer months resulted in seasonal peaks. CONCLUSION MERIN elucidates the spectrum of circulating pathogens, mostly NPEV, causing symptoms of aseptic meningitis, encephalitis and polio-like symptoms and demonstrates seasonal occurrence of pathogens. MERIN contributes to the German national enterovirus surveillance and documents the polio-free status of Lower-Saxony and Bremen.