[Epidemiological characteristics and related influencing factors on Japanese encephalitis in Hainan Province].

OBJECTIVE

To understand the epidemiological characteristics and the influencing factors of Japanese encephalitis (Abbreviated JE) at different periods in Hainan province, and to provide evidence for JE control strategies.

METHODS

Data on JE had been collected since 1952 and related incidence, mortality, fatality rates of JE and the rate of JE vaccination were calculated for four periods: the natural epidemic period (1952-1978), period for inactivated JE vaccine promotion (1979-1986), national immunization program period (1987-1990) and the promotion of live-attenuated JE vaccine period (1991-2007). History on the immunity of JE and data from the monitoring programs on cases and insect vectors were also analyzed.

RESULTS

The average annual incidence in natural epidemic period was 7.12/100,000, which was also the highest among the 4 periods with the mortality rate as 0.89/100,000. The average annual incidence was 0.11/100,000 which was the lowest while the mortality rate was 0.01/100,000 in the period when live-attenuated JE vaccination was under promotion. Since the establishment of JE surveillance system was set up in Hainan province in 2002, the specimen collection rate of JE reported suspected cases had reached 92.8%, while the incidence of confirmed JE cases fluctuated between 0.05/100,000 and 0.2/100,000. Of the confirmed cases, 86% did not have clear history of JE vaccination. The annual average protective rate reached 95.69% in 2004-2007. The density of insect vectors was high in Hainan province. The infection rate of JE in host animal swine, kept rising from April to October, and in some surveillance points, the rate reached 99.3%. The density of insect vector plotted in trans-curve with the infection of host animals.

CONCLUSION

The application of live-attenuated JE vaccine was found to have had significant protective effect on JE in susceptible children. It helped reducing the incidence and controlling the epidemics of JE. It appears feasible to include live-attenuated JE vaccine into the expanded immunization program.