| BackgroundMalaria is a parasitic disease which was transmitted by the bite of mosquitos in the population.With the rapid development of China’s economy in recent years,there is a substantial increase on the number of workers and travelers going abroad,therefore,oversea imported malaria has been becoming a rising public health problem of concern,since these people might get infected by malaria before returning back to China.Currently,on the overseas imported malaria in China,the epidemic,clinical and infection characteristics,and the risk of introducing local transmission of malaria were poor understood.Objectives(1)To systematically present the epidemic situation,demographical and spatiotemporal clustering features of imported malaria,and to explore the origins and species of improted malaria,attack rate,case diagnosis and clinical outcome,as well as the influencing factors contributing to hospitalization and death,so as to identify high risk population and areas for further taking preventive and intervention measures,and then provide guidance to mitigate overseas malaria infection and its severe clinical outcomes.(2)To evaluate the risk of local malaria transmission introduced by different species of imported malaria originated from diverse regions,so as to provide recommendations for monitoring imported malaria cases and investigating the sources of transmission.MethodsData sources in this study including:(1)Surveillance data of local and imported malaria cases from National Disease Surveillance Information Report Management System and the National Institute of Parasitic Diseases Information Management System from 2011 to 2015;(2)Case-based data of imported malaria in nine provinces of China from November 2013 to October 2014;(3)Data of active malaria case screening and mosquito speices investigation in Guangxi Shanglin,from May 2013 to August 2013,(4)Data of national malaria vector population survey,2011-2015.Descriptive analysis was used to analyze the epidemiological distribution of imported and local cases,characteristics of infection and diagnosis.The seasonal trend was fitted with non-linear regression method with cosine function.Kernel Density and Getis-Ord Gi*were used to explore spatiotemporal cluster of imported malaria.The risk facoters on hospitalization and death were exolored by multiple factorsvariable binary classification unconditioned logistic regression model.The transmission risk from imported cases to local cases has been divided into three categories(high,medium and low),by means of adopting the parameters of malaria transmission.ResultsFrom 2011 to 2015,17,745 national malaria cases were reported,and imported cases accounted for 89.3%(15,840 cases),with an average of 3160 imported cases recorded annually.Imported cases were originated from 76 countries of five continents,with Africa accounting for 69.1%and Southeast Asia of 27.4%.P.falciparum was the predominant species(61.6%),followed by P.vivax(30.8%).P.falciparum,and P.malariae and P.ovale were mainly from Africa,and P.vivax mainly from Asia.The cases imported from Africa presented increading trend(p<0.001),while that from Southeast Asia decreased by year(p<0.001).No seasonal peak was identified among the cases from Africa,and which was obvious for both P.falciparum and P.vivax cases from Sountheast Asia(p<0.001).The geographic hot spots of imported P.falciparum were mainly located in the bordering areas between China and Myanmar in the western Yunnan province,Guangxi province and Eastern China.The geographic hot spots of imported P.Vivax were only limited in the border between China and Myanmar in West Yunnan province and East Sichuan province.The malaria attack rate was 21.6%among high-risk groups of oversea workers,and the proportion of asymptomatic infection among all positive Plasmodium infection was 34.4%.Overseas labors accounted for 82.1%of all imported malaria cases.A total of 55.4%of imported malaria cases were hospitalized for treatment,which was significantly higher than that of the local cases(18.6%)(OR=5.0,95%CI=4.4-5.8).The hospitalization proportion of imported P.falciparum and P.vivax cases returning from African are significantly higher than those coming back from Southeast Asia(p<0.001).An average of 24.6 malaria deaths was reported nationwide,with the fatality rate of 6.9‰,which were mainly returned from Africa(89.9%).The group of 45-64 years old(OR=1.9,95%CI=1.3-2.8),P.falciparum infection(OR=10.4,95%CI=3.5-30.7),no previous history of Plasmodium infection(OR=4.1,95%CI=2.6-6.3),and presenting clinical complications(OR=12.1,95%CI=8.3-17.5)were the high-risk factors leading to deaths among the malaria cases.The risk of local transmission introduced by imported malaria was low in the vast majority of areas in China.However,in this study,there are still 15 counties being identified as potential high risk of local transmission introduced by imported malaria from Southeast Asia,where located in the border of China with Maymar.The risk of local transmission by imported P.faciparium malaria from Afria is very low,and five counties faced the medium risk of local trnsmisison by imported P.vivax from Afria.ConclusionsDuring recent years,the epidemic characteristics of malaria in China have changed dramatically,and both the amount and geographic scope of imported malaria were much greater than that of local malaria.Much of the feature of imported malaria from Africa was different from that originated from Southeast Asia,including the epidemic trend,severity of disease and the local transmission risk,etc.Several areas faced the high risk of local malaria transmission reintroducted by overseas imported malaria.National control strategy on imported malaria should be urgently developed to reduce the risk of oversea infection of malaria,improve the timeliness and accuracy of case diagnosis,so as to reduce the incidence of hospitalization and death when the cases returning back to China.In the high-risk areas of local transmission possibly reintroduced by imported malaria,and high-risk areas with local transmission re-established,the capacity of malaria monitoring and investigation should be further strengthened,so as to to prevent the local transmission occurrence and finally achieve the goal of eliminating malaria nationwide in 2020. |
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