Mumps-Related Disease Burden in Japan: Analysis of JMDC Health Insurance Reimbursement Data for 2005-2017.

Background: Mumps vaccination coverage is low in Japan, partly because of its voluntary nature. Although pediatric cases of mumps virus infection are captured by the National Epidemiological Surveillance of Infectious Diseases program under the Infectious Disease Law, there are currently no data regarding the occurrence of mumps and its complications in adults.
Methods: We investigated the annual incidence rates of mumps and its complications based on health insurance reimbursement data for 5,209,660 individuals aged 0-64 years for 2005-2017, obtained from JMDC Inc., to estimate the mumps-related disease burden during this period.
Results: There were three mumps outbreaks (2006, 2010, and 2016) during 2005-2017. The annual incidence of mumps was highest in individuals aged 0-5 years (808-3,792 per 100,000 persons), followed by those aged 6-15 years (658-2,141 per 100,000 persons). The incidence of mumps was higher in females than in males (male/female ratio, 0.90). Among mumps-related complications, the overall incidence (per 1,000 mumps cases) was highest for orchitis (6.6), followed by meningitis (5.8), deafness (1.3), pancreatitis (0.5), and encephalitis (0.3). No cases of oophoritis were noted. The overall incidence of mumps-related complications was 2.5 times higher in males than in females.
Conclusions: This study revealed the disease burden due to mumps and its complications in Japan during 2005-2017. These data suggest the need for mumps-prevention measures in adolescents and adults, as well as in children.