Epidemiologic surveillance of Japanese encephalitis in Kaijiang county, 2002-2006

Objective　The present study was designed to investigate the epidemiological characteristics and prevalence of Japanese encephalitis (JE) in Kaijiang, Sichuan. Methods　Case study of JE was performed from 2002 to 2006, ELISA was used to detect IgM from blood samples of acute phase cases and IgG from blood samples of children under age 10 taken in May each year and swine blood samples taken in June and July each year. Results　The annual average incidence was 3.25/lakh with higher rate observed in plain/hill area than in mountain area (P0.01). The cases which occurred in July and August accounted for 65.93% of the total cases, male cases were more than female cases. The cases among children aged 1-6 years accounted for 83.52%. During 2003-2006, the antibody positive rate in children showed an increase trend without statistical difference by gender (P0.05), but with significant difference by age (P0.01). The annual difference on the positive rate of JE among pigs was significant statistically (P0.01) with the peak occurred in mid or late July, 2002-2005 and mid-June, 2006. The serological confirmation rate of clinical cases was 72.13%. Conclusion　The peak of JE antibody positive rate in pigs and the peak of human case shifted to an earlier date than usual in 2006, which may be due to elevated temperature, increased mosquito density and immunity level. Therefore, it is vital to increase the vaccination coverage rate of JE vaccine for children under 7 years of age and improve mosquito control activity to control the incidence and prevalence of JE.