| ObjectivesTo determine the malaria-prone areas in China and the law that malaria changes in seasons by summarizing the temporal-spatial distribution characteristics of malaria and its distribution characteristics in human population in China in recent years; to build a model for malaria risk prediction by analysing temporal-spatial distribution characteristics of malaria in the Huaihe River Basin and the relationship between malaria occurrence and environmental factors and thereby revealing the temporal-spatial clustering of malaria and the environmental factors that affect malaria occurrence and transmission; to provide a reference method and technique for the study of the temporal-spatial distribution of other insect-borne infectious diseases as well as provide a reference for the monitoring, early warning and scientific prevention and control in the malaria-prone areas.Methods1. Methods for data collection and processingNetwork-based report data of malaria epidemics, population information, data from weather monitoring stations, branch distribution of river and GDP per capita in the study areas were collected, Excel was used to compare, screen, arrange in order and sort the data, as well as the environmental data and incidence data were correlated by unifying the criteria for mutual relationship between different data; Kriging was used to estimate the meteorological data in unknown areas; and SuperMap GIS was used to compute the drainage density in all districts and counties of the Huaihe River Basin.2. Analytical methods2.1Building geographic information database The incidence of malaria in different study areas and different years was related with the1:4,000,000electronic map, and ArcGIS9.0was used to build a geographic information database at national province (municipality and autonomous region)-level and and at county (city and district)-level of the Huaihe River Basin.2.2Descriptive analysis methodsDescriptive epidemiology was used to analyse the temporal and spatial distribution characteristics of malaria and its distribution characteristics in human population in whole China in terms of time, space and population, and the map by ArcGIS was used to show the spatial distribution characteristics of malaria in whole China and the Huaihe River Basin.2.3Temporal-spatial clustering analysisSaTScan was used to perform purely spatial clustering analysis, purely temporal clustering analysis and purely temporal-spatial clustering analysis to explore the temporal-spatial clustering areas and epidemic periods of malaria in the Huaihe River Basin and to determine the temporal-spatial distribution characteristics of malaria-prone areas in the Huaihe River Basin.2.4Partial correlation analysis and Spearman rank correlation analysisPartial correlation analysis was used to determine the relationship between malaria occurrence and meteorological factors; Spearman rank correlation analysis was used to measure the relationship between malaria occurrence and drainage density and GDP per capita.2.5Binomial logistic regression and negative binomial regression analysisBinomial logistic regression was used to explore whether there are natural factors that affect malaria occurrence; negative binomial regression analysis was used to explore the environmental factors that affect malaria transmission to build a negative binomial regression model and evaluate it.Results1. The distribution characteristics of malaria in whole China1.1Overview of malaria epidemics in whole ChinaIn2006-2010, a total of154,711cases with malaria were reported in whole China, where94cases died, the average annual incidence was2.34per100,000, and the occurrence decreased gradually year by year. Of the cases, tertian malaria accounted for79.42%, falciparum malaria accounted for5.02%and the rest that were not classified accounted for15.56%. Of the dead cases, falciparum malaria accounted for80.85%, tertian malaria accounted for11.7%and the rest that were not classified accounted for7.45%. Of the reported cases, the laboratory-diagnosed cases accounted for63.06%and the clinically diagnosed ones accounted for36.94%.1.2The spatial distribution of malaria epidemics in whole ChinaOver the five years, the total number of malaria occurrence in Anhui, Hainan and Yunnan province accounted for77.48%of the total one in whole China. The average annual incidence in the three provinces ranked the top three, reaching27.29per100,000,23.28per100,000and11.73per100,000respectively, the one in Henan,Guizhou, Hubei and Tibet came second, accounting for1per100,000-5per100,000, and the one in most parts of Northeast and Northwest China was lower than0.1per100,000. Of the cases with tertian malaria, the ones in Anhui province were the most in number, accounting for58.59%, the ones in Yunnan and Henan province came second, accounting for15.58%and11.52%respectively, and the one in each remaining province and region was lower than4%, where no such cases were reported over the5years in Inner Mongolia. Of the cases with falciparum malaria, the ones in Yunnan province were the most in number, accounting for69.07%, and the one in each remaining province and region was lower than6%, where no such cases were reported over the5years in Tibet and Ningxia.1.3The temporal distribution of malaria epidemics in whole ChinaThe malaria epidemics were mainly clustered in summer and fall season (July-October), where the incidence was highest in August. The incidence was lower in winter season (November-February), where the one in February was lowest. The malaria occurrence in different areas tended to be differently seasonal, and further such seasonal occurrence declined year by year.1.4The distribution of malaria epidemics in human population in whole ChinaRegarding the sex, the male patients with malaria were the majority, accounting for64.8%. Regarding the occupation, the farmers accounted for63.67%, and the students and urban residents came second, accounting for14.52%and10.12%respectively. Regarding the age, the incidence of malaria in over-66-aged seniors was higher, reaching3.41per100,000, and the one in infants aged0-5was lower, reaching1.32per100,000.2. Temporal-spatial clustering analysis of malaria in the Huaihe River Basin2.1The temporal-spatial distribution characteristics of malaria in the Huaihe River BasinIn2006-2010, the total number of malaria occurrence in the Huaihe River Basin accounted for62.42%of the total one in whole China. In the Basin, the average annual incidence was11.53per100,000, approximately5times that in whole China, and the occurrence tended to decline year by year. In Guoyang, Mengcheng, Lixin and Suixi County and Lieshan District of Anhui province and Yongcheng City of Henan province, there was a higher average annual incidence reaching100per100,000. In the Basin, the malaria occurrence was mainly clustered in July-October, where the incidence was highest in August. The incidence was lowest in February. The seasonal occurrence declined year by year.2.2Spatial clustering analysisIn2006, in the clustering area, the coordinates of center were (33.92N,116.77E) and the radius was71.64km covering Suixi County and14neighboring counties. In2007-2009, the coordinates of center were (33.27N,116.56E), and the radius was92.78km covering Mengcheng County and29neighboring counties. In2010, the coordinates of center were (33.27N,116.56E), and the radius was109.80km covering Mengcheng County and35neighboring counties.2.3Temporal clustering analysisIn2006, the relative time when malaria was prone to occur fell in July-November. In2007-2009, such time fell in June-October. In2010, the time fell in May-October.2.4Space-time clustering analysisIn2006-2010, in the Huaihe River Basin, the coordinates of center in the clustering area were (33.27N,116.56E) and the radius was92.78km covering Mengcheng County and29neighboring counties, where the relative time when malaria was prone to occur lasted from June,2006to November,2008.2.5The temporal-spatial distribution of30malaria-prone areas of the Huaihe River Basin In the malaria-prone areas of the Huaihe River Basin,25counties suffered from malaria outbreaks throughout the year, wherein the outbreaks appeared to be significantly seasonal and were mainly clustered in July-October. The incidence was highest in October and lowest in February. The incidence was higher in Guoyang, Suixi and Mengcheng County and Lieshan District.3. Relationship between malaria occurrence and environmental factors in the Huaihe River Basin3.1The correlation between malaria incidence and environmental factorsIn the time when malaria was prone to occur in the Huaihe River Basin, the occurrence showed a significant positive correlation with the maximum temperature in the current month, the rainfall in the previous month and drainage density, and it showed a significant negative correlation with the rainfall in current month and GDP per capita. The occurrence was not significantly correlated with the maximum temperature in the previous month, the minimum temperature in the current and previous month, the mean temperature in the current and previous month as well as the relative humidity in the current and previous month.3.2Environmental factors that caused possible malaria occurrenceIn the time when malaria was prone to occur, there was possibility that malaria would occurred in the areas where the maximum temperature in the current month exceeded27.25℃.3.3The environmental factors which affect the malaria transmissionIn the areas where malaria occurred, the rainfall(Ro) in the current month was unduly heavy, the malaria incidence(Y) was lower, and the negative binomial regression model for predicting malaria transmission was Y=exp(17.1897-0.2387Ro).Conclusion1. In2006-2010, the malaria incidence in China dropped drastically, but the fight against malaria is still grim. The malaria transmission in China shows significant spatial heterogeneity:the malaria occurrence is mostly clustered in the Huaihe River Basin, the southwestern borders and Hainan Island. Temporally, the malaria occurrence in China is mostly clustered in summer and fall season, and the seasonal occurrence declines year by year. Regarding the Chinese patients with malaria, they are mostly farmers and male, where the old persons have a higher incidence. 2. The malaria epidemics in the Huaihe River Basin appears to be significantly clustered spatially and seasonal temporally. Spatially, there are different malaria-clustered areas in different years, where Mengcheng County and its29surrounding counties are in the majory. Temporally, there are different malaria-clustered time in different years, which generally falls in June-October. Malaria occurs throughout the year in most malaria-prone counties (cities and districts), where the epidemics start to spread in spring and there is a higher incidence in fall.3. In the time when malaria is prone to occur in the Basin, the occurrence has a correlation with the maximum temperature in the current month, the rainfall in the previous month, drainage density, the rainfall in the current month and GDP per capita, as well as it is not much related with the weather factors including relative humility. The possible malaria occurrence is subject to the maximum temperature in the current month. In the areas where malaria occurs, the degree of transmission is subject to the rainfall in the current month. The environmental factors can affect the occurrence and transmission of malaria, therefore, the monitoring of such factors is available for predicting the possible tendency of malaria in the Basin. |
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