Recently, we have noticed an increase in the number of patients with mumps in Incheon, Korea. The aim of this study is to estimate the regional trend in mumps incidence and to evaluate the factors related to the recent increase.

We reviewed the medical records of 66 patients with mumps who had been admitted to Incheon St. Mary's Hospital from July 1999 to June 2009. We compared the differences in records between "outbreak, 2009" and "nonoutbreak, 2000-2008."

Of the 66 patients, 35 (53%) were admitted in 2009, and 31 (47%) were admitted between 2000 and 2008. Most of the patients admitted during the outbreak were over 15 years of age (80.0%), were born before 1993 (77.1%), and had received a single dose of mumps vaccine (62.9%). There were no significant differences in contact history, present address, clinical manifestations, and complications, except for orchitis, between the two groups.

There was a sharp increase in the number of inpatients with mumps who were born before 1993 and who were over 15 years of age. We recommend that a booster vaccination be considered for adolescents and young adults born before 1993 who are susceptible to mumps infection due to their reduced opportunities for receiving two doses of mumps vaccine.