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* Author for correspondence: S.-I. Cho, M.D. Sc.D., Professor, Department of Epidemiology, School of Public Health, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea. (Email: [email protected])
INTRODUCTION
Mumps is an acute febrile illness characterized by swelling of parotid glands. The mumps incidence decreased dramatically after the widespread use of vaccine, mostly in combination with vaccines for measles and rubella (measles–mumps–rubella (MMR) vaccine). Mumps vaccination has been used globally during several decades, but the disease is still one of the leading pathogen among vaccine-preventable outbreaks in the world today [1]. More recently, mumps resurgence was noted in many countries despite high two-dose MMR vaccination coverage [2]. Suggested causes of resurgence vary by country and region, but there are evidences that insufficient vaccine efficacy, mismatch between vaccine and circulating virus, and intense social contacts may have contributed to the mumps outbreaks [3–5].
In South Korea, MMR vaccine has been included in NIP (National Immunization Program) since 1985 [6]. The vaccination schedule was updated with two MMR doses given at 12–15 months and 4–6 years in 1997. Following that, reported mumps cases decreased from 5000 to 8000 cases annually to <2000 cases per year [7]. In 2000s, however, the resurgence of mumps was noted primarily among school-aged children and adolescents.
The geographic differences in outbreak during the 2000s resurgence have not been assessed previously. As mumps tend to cluster geographically where susceptible population reside in close proximity, spatial analyses may bring important insight to detect and predict the incidence patterns of mumps. In this study, we sought to understand spatial patterns in mumps incidence to give an indication to the geographical risk of the disease in the settings with high MMR vaccination coverage.
METHODS
South Korea occupies around 100 032 km2, with population of approximately 50·2 million in 2013. It is divided into 16 provinces (si-do), which are subdivided into 252 districts (si-gun-gu). We grouped the provincial level according to their geographical proximities: Seoul-Incheon-Gyeonggi (northwest); Daejeon-Chungcheong (midwest); Gwangju-Jeolla (southwest); Gangwon (northeast); Daegu-Gyeongbuk (mideast); and Busan-Gyeongnam (southeast) (Supplementary Material).
In Korea, the case-based surveillance that used a set of case definition for suspected and confirmed mumps cases is being practiced. It is obligatory for all physicians to report the laboratory-confirmed or clinically suspected mumps...