An Outbreak of Japanese Encephalitis in Adults in Northern China, 2013: A Population-Based Study

Background: A Japanese encephalitis (JE) epidemic occurred in 2013 in China. The aim of this study was to determine the spatial-temporal pattern of JE cases in adults occurring in 2013, as well as identify potential hotspots of incidences in the afflicted regions in China. Methods/Principal Findings: To generate a spatial-temporal pattern of JE cases in China, epidemiological and demographic data between 2011 and 2013 were collected. Our results indicate that the total number of JE cases in 2013 was significantly higher compared with those in 2011 and 2012. While the incidence of JE in individuals aged less than 15 years decreased in 2013, the incidence rate increased substantially in those aged 15 years and older. The population aged over 40 years was associated with the greatest increase of JE. Demographic analysis revealed a consistent increase in the proportion of JE cases aged 15 years and older in 2013 (42%) compared with that in 2012 (15%). In addition, JE cases from areas located between 35 degrees N, 114 degrees E and 40 degrees N, 120 degrees E in northern China were found to account for 27.17% of total JE cases nationwide in 2013, compared with 2.21% and 3.13% in 2011 and 2012, respectively. In these northern regions, the group aged 15 years and older represents the predominant population with JE, accounting for 73% of total cases. Further cluster analysis identified a large number of hotspots of JE in adults (>15 years of age) in northern China. Conclusions/Significance: Unlike the JE epidemics primarily in children below 15 years old in southern China, a significant outbreak of JE occurred in northern China in 2013, with the older age groups being the primary population affected. The increasing incidence of JE in adults has become an important public health issue and poses a new challenge to the successful prevention and control of JE in China, as well as other countries in East Asia.