The Analysis Of Spatio-temporal Character Of Malaria Epidemic Situation And Its Determinants

Background:Malaria is one of the important verminosis caused by a parasite that is transmitted to humans by a female mosquito's bite.Some 3.2 billion people live in areas at risk of malaria transmission in 107 countries.Each year 300 million are diagnosed with malaria and more the one million people die of malaria.There were serious malaria epidemics in our country during 1950's and 1960's.Huge progress has been made in preventing and treating malaria after efforts for over half a century.The incidence rate of malaria reached the lowest level at the end of last century, and started to increase again at the central Anopheles sinensis area represented by Anhui province located 32°north latitude since 2000.Some small and large outbreaks at local areas were also reported.The complexity of malaria,its transmission and infection risks is determined by parasite,human host,environment and the interactions between them.The GIS,GPS and RS(abbreviated as 3S technology) have become the new methods and technical measures to study malaria and other zoonotic and vector-borne diseases.The combination of statistics and space technology has become the new research direction.Objectives:The study explores the spatio-temporal characters of malaria epidemic situation and its determinants in Anhui province since 1990 in order that provide empirical evidence for the prevention and control policy of malaria's in the Anhui and similar districts. In addition to it also pave a way for the synthetic technology for malaria research field by using spatial statistics and 3S technologies,which can be used in the other similar study.Methods:The surveillance data of malaria epidemic was collected and digital maps at the county(1:1 000 000),township(1:50 000) levels were processed.The township level data for the temperature,precipitations,altitude,NDVI,humidity and water environment,also including the population and GDP was extracted through the spatial analysis technology, and the corresponding GIS database was created.Then collecting village level data for the life styles,behavior factors,and disease diagnosis and treatment information of local residents in the high incidence rate area in Huaibei districts by the sample field survey, and water body locations can be obtained by GPS localizer.The village level analysis database was also created accordingly.Spatio-temporal scanning cluster analysis, time-series analysis,principal component analysis and logistic regression model,and Poisson regression model was used and the software used includes Arc GIS 9.0, SaTScan7.0,SAS9.1 and SPSS13.0.Results:1.The Huaibei area in Anhui province from 2004 to 2006 is the hot spot of malaria epidemic since 1990s',the duration of malaria transmission season was extended in Huaibei area.2.Longitudinally significant correlation was found between malaria incidence rate and environmental factors(temperature and precipitation).The positive correlation existed between the 'increase' of monthly average temperature and monthly malaria incidence rates when the data were staggered to allow a lag of 0-3 month.The increasing monthly precipitation was accompanied by increase of monthly malaria incidence rate when they were transformed by 1-3 month lag.The correlations were significant for the malaria incidence rates with at least one month lag.This indicated that the relationship between precipitation and malaria incidence was relatively slow.3.The incidence of malaria was related to temperature,precipitation,NDVI and altitude at township level analysis in Anhui province.Winter/the lowest temperature,annual precipitation,altitude and NDVI are the influencing factors for malaria.When other variables in the model are controlled,the higher the value of former 3 factors is the less chance of the malaria occurs.However,the increase of NDVI increases the chances to have malaria.4.The poor life style and local behavior of residents in this area put them in higher risk to get infected.The results show that if the percentage of outdoor sleeping increases by 1%, the relative ratio of infected malaria will increase 8%.The cultivation of bean crop will increase the risk of infected malaria. 5.The ARIMA time series model established based upon the incidence data of Jan.2000 to May.2007,forecast that the incidence of malaria in June 2007 is 5.437/100 000(CI 2.308/100 000,12.808/100 000).The real incidence is 5.334/100000.The relative forecast error is 1.9%.Conclusions:This study mainly answered the reasons of the rebound of malaria epidemics in the new spatio-temporal hot spot at Anhui province since 2000.The combination of 3S spatial analysis techniques and statistics were used to identify the main factors explaining the differences of incidence rate between southern and northern areas.In addition to the terrain and natural environment in Huaibei area,the tillage style and poor lifestyle behavior factors increased contact with mosquito,so this increased the chance to be infected for the residents.The results nail down the focus of malaria prevention and control,which is of momentous current significance for the anti-malaria.The results did not support that the effects of the timeliness of malaria diagnosis,but based upon the theory of controlling infectious source,it is very important to find and treat patient timely in order to control the malaria.The research will lay a solid foundation for early warning and early forecast in the central areas such as Anhui.Moreover,time series model can be used to fit the changing trends of malaria incidence rate at different times.If the population immunization status,population mobility, prevention measures and other susceptibility indicators are relative stable,it can be used to forecast the incidence of malaria in the future,and to provide services for prevention and control of malaria epidemics.