Epidemiology of Japanese encephalitis in counties in three gorges reservoir area and non-three gorges reservoir area, Chongqing, 2004-2014

Objective To understand the epidemiological characteristics of Japanese encephalitis (JE) in Chongqing during 2004-2014, and provide evidence for JE prevention and control. Methods The Descriptive epidemiological analysis was conducted by using the incidence data of JE in the counties in and outside three gorges reservoir area (TGRA) in Chongqing during the periods before (2004-2008) and after (2009-2014) the inclusion of JE vaccination in immunization program. Results From 2004 to 2014, the average incidence of JE was 0.82/lakh in TGRA counties and 1.12/lakh in non-TGRA counties, and the case-fatality rate was 3.25% and 2.82%, respectively. The incidence trends of JE in TGRA counties and in non-TGRA counties were similar, and more cases occurred in males than in females. The cases were mainly reported during July-August, and most cases were aged 15 years (98.77%). In TGRA counties, the JE incidence decreased from 1.34/lakh during 2004-2008 to 0.36/lakh during 2009-2014. In non-TGRA counties, the JE incidence decreased from 1.62/lakh during 2004-2008 to 0.68/lakh during 2009-2014, the difference was significant (P 0.01). In non-TGRA counties, the case fatality was 3.96% during 2004-2008 and 0.45% during 2009-2014, and in TGRA counties, the case fatality was 3.54% during 2004-2008 and 2.36% during 2009-2014. After routine JE immunization, the incidence of JE in age group 0-14 years in TGRA counties were lower than 0.05/lakh except age groups 3 years and 4 years, but the incidence of JE in age group 0-14 years in non-TGRA counties were lower than 0.10/lakh. Conclusion The incidence pattern and seasonal distribution of JE in Chongqing (both in TGRA counties and in non-TGRA counties) were similar to national ones. After routine JE immunization, the incidence of JE in age group 0-14 years declined significantly in TGRA counties, suggesting that the environmental change in TGRA had no obvious impact on JE incidence and the JE immunization measure was effective, but improvements are still needed to protect risk populations.