Enhancing detection of severe enterovirus infections: A data linkage study of ICD-10 codes with national enterovirus laboratory data, Denmark, 2010 to 2023

INTRODUCTIONEnteroviruses cause symptoms ranging from mild skin manifestations to severe neurological diseases, such as polio. Despite global eradication efforts, poliovirus was detected via environmental surveillance in multiple European countries in 2024 and 2025.AIMWe aimed to assess the epidemiology of enteroviruses in Denmark, using national laboratory surveillance and hospital discharge registries, and to determine the accuracy of enterovirus registration.METHODSHospital admission data from 1 January 2010 to 31 December 2023 were linked to laboratory surveillance enterovirus data to identify and categorise admissions with an enterovirus-specific ICD-10 code and/or enterovirus-positive test. The accuracy of diagnosis coding and positive enterovirus tests was assessed against an estimated 'true population' using a capture‒recapture analysis.RESULTSAmong patients with an ICD-10 enterovirus code and a positive enterovirus test (n = 1,186), 69% had a central nervous system diagnosis. Patients with ICD-10 enterovirus codes only (n = 3,434) were younger and primarily had hand, foot and mouth disease. Patients positive for enterovirus without an enterovirus diagnosis (n = 3,263) frequently exhibited respiratory symptoms. The combined accuracy of ICD-10 codes and enterovirus tests was 46.3% (95% confidence interval (CI): 44.3-48.4) against an estimated 'true population' of 28,193 (95% CI: 26,929-29,457) enterovirus infections.CONCLUSION: It is important to combine laboratory data and ICD-10 codes to gain comprehensive understanding of the enterovirus epidemiology and identify areas for improvement in enterovirus surveillance. Despite exceptional registries, the Danish system may still overlook early cases of emerging or severe enterovirus infections because of limited clinical awareness of these infections and the challenges associated with voluntary test registrations.