[Relationship between Echovirus Epidemics and Incidence of Aseptic Meningitis following Mumps Vaccination Based on Previous Japanese Reports: Possibility of Misclassification of Echovirus Infection in Previous Reports].

Objectives: In Japan, the vaccination for mumps has been on a voluntary basis since 1993 because of safety concerns arising from the high incidence of aseptic meningitis associated with Japanese mumps vaccine strains. However, recent reports on the voluntary mumps vaccination have described the decreased incidence of postvaccination aseptic meningitis for unknown reasons. To explore the underlying reason for this decrease, we analyzed the influence of echoviruses, the most common causative viruses for community-acquired aseptic meningitis, on the previously reported incidence of aseptic meningitis following mumps vaccination.

Methods: We used available data on the yearly number of cases of echovirus detection from the Infectious Agents Surveillance Reports issued by the National Institute of Infectious Diseases as well as previously reported nationwide data on the incidence of postvaccination aseptic meningitis.

Results: The incidence of postvaccination aseptic meningitis tended to be higher during the period of an echovirus epidemic and lower during the period without such as epidemic.

Conclusions: The present ecological trend analysis suggests the influence of echovirus epidemics on the previous reported incidence of aseptic meningitis following mumps vaccination. It is necessary to carry out a differential diagnosis of echovirus infection to identify the true causative viruses in aseptic meningitis following mumps vaccination.