| BackgroundFlooding is defined as an overflow of surface runoff that submerges towns and farmland,which is caused by long lasting and heavy rainfall and could further lead to both agricultural and other financial losses as well as casualties.From the 21st century,the frequency of severe flooding disasters across the world is greatly increased.The Intergovernmental Panel on Climate Change(IPCC)also projects that climate change will bring about changes of extreme weather events with respect to frequency,intensity,duration and the areas affected under the context of global warming.Our country is one of the worst hit areas by floods in the world.Besides,with the rapid socioeconomic development,urbanization as well as the gathering of population and assets in recent years,the social impacts and the healthy problems caused by floods attract more concern.After floods,changes of ecological environment concerning water source,relative humidity and temperature,as well as human immune system will cause a number of infectious diseases including vector-borne diseases.enteric infectious diarrhea and respiratory tract infections,which bring about severe adverse effects on public health.Vector-borne diseases refer to a group of diseases transmitted by pathogen vectors including mosquitoes,flies,sand flies,lice,fleas,ticks and mites,most of which are natural focal diseases.Although the number of vector-borne diseases cases accounts for only 5%?10%of total infectious cases in our country every year,the mortality is up to 30%?40%of the total death counts due to infectious diseases.Epidemic encephalitis B,also known as Japanese encephalitis(JE)is a serious mosquito-borne viral encephalitis caused by JE virus,whose main symptoms are neurological injuries.It is endemic in Asia and northern Australia.According to the World Health Organization(WHO),it is estimated that at least 45,00 cases of JE have occurred annually across the world,with a 20?30%case-fatality rate.Although a couple of studies at home and abroad have confirmed that rainfall,relative humidity and temperature are associated with the incidence of JE cases,little is known about the quantitative impact of floods,as natural disasters related with rainfall,on cases of JE.Besides,most previous studies are based on monthly or weekly data;lack of research has studied the relationship between JE and flood on a daily basis.Therefore.this study was undertaken to examine the relationship between floods and JE in Sichuan Province on a daily scale and to confirm the impacts of both temperature and relative humidity on JE cases,to better understand the impact of floods on mosquito-borne diseases.Objectives(1)To detect the cluster areas of JE cases in Sichuan Province.(2)Examining the quantitative relationship between floods and JE in various lagged days.(3)Examining the quantitative relationship between meteorological factors and JE in various lagged days.MethodsCluster areas of JE cases in Sichuan were detected by dictating the distributional graph of reported JE cases from 2005 to 2012 using ArcGIS.The two cities with most JE cases in the cluster areas were selected as the study cites.Cases of JE were collected daily from National Notifable Disease Surveillance System(NNDSS);Data on floods and meteorological variables were collected from China MeteorologicalData Sharing Service System and the Yearbook of Meteorological Disasters in China.The time-stratified case-crossover study was applied to quantify the impact of floods and meteorological factors on daily Japanese encephalitis(JE)cases from 2005 to 2012 in two selected cities in Sichuan Province.Using conditional logistic regression analysis,we calculated the odds ratios(ORs)and 95%confidence intervals(CIs)at different lagged days.Generalized additive model(GAM)was used for sensitive analysis.Relative risks(RRs)and 95%CIs of floods at a certain city on JE at different lagged days were calculated by using a GAM,adjusting for daily average temperature,daily average relati-ve humidity,and seasonal and long term temporal trends,which were conducted to confirm the results of time-stratified case-crossover study in our last step.ResultsMost JE cases in Sichuan Province clustered in eastern areas,with zero cases detected in western areas.A total of 611 notified JE cases were identified during the study period in Nanchong city.The median of case distribution was 3.6-year-old.In Luzhou city,there are 493 JE cases being reported during the period,with a median age of 4.1-year-old.The age distributions in both cities were biased to children under 4-year-old.The logistic regression analysis showed that floods were positively associated with JE from 23-day lag to 25-day lag in Nanchong city,with the greatest effects at 24-day lag(OR=2.19.95%CI:1.34-3.58).In Luzhou city.we also found that floods were posit:ively associated with JE from 22-day]ag to 24-day lag,with the greatest effects at 23-day lag(OR?11.84.95%CI:1.16-2.92).The logistic regression analysis also indicated that both average temperature and relative humidity in Nanchong city had positive associations with JE cases,with the strongest effects at 24-day lag and 25-day lag(OR=1.24,95%CI:1.15-1.34 for AT at lag 24;OR=1.05,95%CI:1.03-1.08 for ARH at lag25),respectively.Similarly,there were significant associations between JE and daily average temperature as well as relative humidity in Luzhou city,with the strongest lagged effect at 16-day lag(OR=1.26,95%CI:1.15?1.39)and at 15-day lag(OR=1.07,95%CI:1.04-1.09),respectively.The results of sensitive analysis demonstrated that floods were positively associated with JE from 19-day lag to 21-day lag and from 23-day lag to 25-day lag in Nanchong city,with the greatest effects at 21-day lag(RR=1.50,95%CI:1.08-2.09)and at 23-day lag(RR=1.50,95%CI:1.07-2.09)after 21-lag day.Conclusions(1)JE cases in Sichuan Province clustered in the eastern areas.(2)Floods can significantly increase the risk of JE in the study area.(3)Daily average temperature and relative humidity are also risk factors for the incidence of JE cases. |
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