30-year trends in admission rates for encephalitis in children in England and effect of improved diagnostics and measles-mumps-rubella vaccination: a population-based observational study

Background Encephalitis is a serious neurological disorder, yet data on admission rates for all-cause childhood encephalitis in England are scarce. We aimed to estimate admission rates for childhood encephalitis in England over 33 years (1979-2011), to describe trends in admission rates, and to observe how these rates have varied with the introduction of vaccines and improved diagnostics. Methods We did a retrospective analysis of hospital admission statistics for encephalitis for individuals aged 0-19 years using national data from the Hospital Inpatient Enquiry (HIPE, 1979-85) and Hospital Episode Statistics (HES, 1990-2011). We analysed annual age-specific and age-standardised admission rates in single calendar years and admission rate trends for specified aetiologies in relation to introduction of PCR testing and measles-mumps-rubella (MMR) vaccination. We compared admission rates between the two International Classification of Diseases (ICD) periods, ICD9 (1979-94) and ICD10 (1995-2011). Findings We found 16 571 encephalitis hospital admissions in the period 1979-2011, with a mean hospital admission rate of 5 . 97 per 100 000 per year (95% CI 5 . 52-6 . 41). Hospital admission rates declined from 1979 to 1994 (ICD9; annual percentage change [APC] -3 . 30%; 95% CI -2 . 88 to -3 . 66; p< 0 . 0001) and increased between 1995 and 2011 (ICD10; APC 3 . 30%; 2 . 75-3 . 85; p< 0 . 0001). Admissions for measles decreased by 97% (from 0 . 32 to 0 . 009) and admissions for mumps encephalitis decreased by 98% (from 0 . 60 to 0 . 01) after the introduction of the two-dose MMR vaccine. Hospital admission rates for encephalitis of unknown aetiology have increased by 37% since the introduction of PCR testing. Interpretation Hospital admission rates for all-cause childhood encephalitis in England are increasing. Admissions for measles and mumps encephalitis have decreased substantially. The numbers of encephalitis admissions without a specific diagnosis are increasing despite availability of PCR testing, indicating the need for strategies to improve aetiological diagnosis in children with encephalitis.