Despite decline in mumps encephalitis, all-cause encephalitis continues to rise
Although hospital admissions for encephalitis related to measles and mumps has decreased significantly in England, the incidence of all-cause childhood encephalitis is increasing, according to a recent study published in Lancet Infectious Diseases.
“Childhood encephalitis is of great health importance, with long-term morbidity occurring in up to 50% of affected individuals. However, little is known about the epidemiology of all-cause childhood encephalitis in England because previous studies have either involved a specific etiological group — for example, viral encephalitis — or a predominantly adult population,” Mildred A. Iro, MBBS, from the University of Oxford, and colleagues wrote. “Study of the epidemiology in terms of etiology and time trends is important to aid further understanding of patterns of the disease, gain useful information for future research and aid priority setting in the prevention and treatment of encephalitis.”
The researchers examined data on hospital admission rates for childhood encephalitis, collected between 1979 and 2011, to estimate and describe trends in admission rates, as well as reflect upon how vaccines and improved diagnostics have affected this data.
The researchers conducted a retrospective analysis of admission statistics for pediatric admissions for encephalitis from the ages of 0 to 19 years, provided by the Hospital Inpatient Inquiry (1979-1985) and Hospital Episode Statistics (1990-2011).
Annual age-specific and age-standardized admission rates in each calendar year were analyzed in addition to trends in admission rates with a noted etiology with the introduction of PCR testing and measles-mumps-rubella (MMR) vaccines. Two International Classifications of Diseases (ICD) periods were compared: ICD9 (1979-1994) and ICD10 (1995-2011).
During the observed timeframe, 16,571 hospital admissions for encephalitis occurred (5.97 in 100,000 per year). Although hospital admission rates decreased in ICD9 (-3.30% annual change; 95% CI -2.88 to -3.85; P <.0001), rates increased in ICD10 (3.30% annual change; 2.75 to 3.85; P <.0001).
Although severe reductions were observed in admissions for measles (97%) and mumps encephalitis (98%) following the introduction of the two-dose MMR vaccine, the rates of hospital admission for children with encephalitis with unknown etiology rose 37% after PCR testing.
“Although the reason for the initial decline in all-cause encephalitis is unclear, a major component is probably the reduction in measles and mumps encephalitis admissions with MMR vaccination — including a reduction in cases of unspecified etiology that were, in fact, caused by mumps and measles,” Iro and colleagues wrote. “The reasons for the increase in all-cause encephalitis in the later years need consideration.” —by Katherine Bortz
Disclosure: The researchers report no relevant financial disclosures.