Identifying And Projecting Flood-related Sensitive Infectious Diseases

Background:Climate change would be the most serious global health threat in the 21st century. It affects human physical and mental health both directly, through climatic extremes, and indirectly, through environment pollution, promotes reproduction of pathogens, replacement of refugee and so on. Over the last decade, flooding has been the most common type of disaster globally. The number of victims was far more than the sum of population affected by other natural and technical disasters, with economic losses of nearly US $185 billion. The greatest potential flood hazard is in developing countries where there is a lack of disaster management systems and resources. China is one of the most flood-prone countries in the world. Large population, complicated topography, climate conditions and rapid urbanization process promote a high risk of flood exposure.Infectious diseases are the most common diseases during flood events. The deteriorated living condition, the lack of clean water and health service facilities can assist the transmission of infectious diseases. Although some literature have analyzed the relationship between flood event and a specific infectious disease, no previous studies have quantitatively identified the sensitive diseases from arrange of infectious diseases in different routes of transmission. Most past study on flood events and various infectious diseases were systematic reviews. Especially in China, limited studies have reported the sensitive flood-related infectious diseases. Literature review indicated that, firstly, the different selection of study areas, flood events and methods in past studies caused the inconsistent results of relationship between flood and infectious diseases. Secondly, our study will include several flood events happened in the same study area with analysis from both temporal and spatial analyses, which can obtain a more reliable result than other studies. Thirdly, few studies have examined the risks of different levels of flood events. According to the flood classification defined by the Comprehensive Study Group of Major Natural Disasters of the State Science and Technology Commission in China, our study will classify the flood events into moderate and severe levels, and detect their different impact on population health. Fourthly, under the scenarios of future flood events, few projections on flood-related infection cases were conducted. The excessive burden of sensitive infectious diseases induced by different levels of flood event in the future will also be projected. This study has important implications for public interventions and will provide scientific evidence in responding to floods related health outcomes.Objectives:1. The study was to establish the database of flood events in anhui province from 2005 to 2011 and build up the framework of identifying flood related sensitive diseases.2. The study aimed to quantify the risks of various flood events on infectious diseases as well as spatial distribution of diseases during flood disaster, then identify flood related sensitive infectious diseases.3. To project the flood related excessive burden of sensitive infectious diseases in 2020 and 2030.Methods:From 2005 to 2011, case data of 39 national notifiable diseases in Anhui province were collected. Daily number of cases for each disease, population, independent variable (flood events) and control variables (daily meteorological variables, socio-economic variables) were arranged by date, and this could be the time series database; in the spatial analysis, the study area included all seventy eight counties in whole Anhui Province. All the independent (flood event) and dependent variable (incidence of each disease) and control variables (meteorological and socio-economic factors) were included in county-level, and this is the geographical information database.The temporal and spatial distribution of flood events during April and September from 2005 to 2011 were collected, the most serious flood-hit areas (Bengbu, Bozhou, Fuyang, Huaibei and Suzhou) were selected to be the study area in time series analysis. Cross-correlation analysis was conducted to explore the lagged effects of flood events and meteorological variables on infectious diseases. The lag values with the maximum correlation coefficient for floods and the confounding factors were selected for inclusion in the subsequent analysis to quantify the impact of various flood events on infectious diseases.The Huai River Basin flood event happened from July 1st to 24th in 2007 was chosen to be a case for spatial study. Spatial autocorrelation and regression analysis were attached to detect disease aggregation and association between diseases and flood event respectively. Lagged effect was controlled in spatial analyzes. The relative risks of included diseases in flood affected areas were calculated to identify the sensitive infectious diseases from geographical aspect.The RRs of infectious diseases due to exposure of various flood events, the scenarios of future population growth and flood events were the basis for the projection. The ranges of increased disease burden for sensitive infectious diseases in each scenario were projected.Results:1. Huai River Basin, especially Bengbu, Bozhou, Fuyang, Huaibei and Suzhou were the flood prone areas in Anhui province.2. The results from temporal analysis indicated that, the impact of flood events on infectious diseases including both negative and positive effects. The incidence risk of the following diseases would increase during flood events. Bacillary and amebic dysentery (the RR caused by moderate flood events was estimated to be between 1.17 and 1.34, the RR caused by severe flood events was estimated between 1.34 and 1.51), Other infectious diarrhea (the RR caused by moderate flood events was estimated to be 1.14, the RR caused by severe flood events was estimated to be 1.09), HAV infection (the RR caused by moderate flood events was estimated to be between 1.38 and 1.40, the RR caused by severe flood events was estimated between 1.75 and 1.77), Japanese encephalitis (the RR caused by moderate flood events was, estimated to be 1.95, the RR caused by severe flood events was estimated to be 3.72), Tuberculosis (the RR caused by moderate flood events was estimated to be between 1.28 and 1.30, the RR caused by severe flood events was estimated between 1.48 and 1.49), Measles (the RR caused by moderate flood events was estimated to be between 3.62 and 3.63, the RR caused by severe flood events was estimated to be 1.27).The incidence risk may decrease for the following infectious diseases. Mumps (the RR caused by moderate flood events was estimated to be between 0.71 and 0.72, the RR caused by severe flood events was estimated between 0.26 and 0.28); Rubella (the RR caused by moderate flood events was estimated to be between 0.45 and 0.46, the RR caused by severe flood events was estimated to be 0.22); Varicella (the RR caused by moderate flood events was estimated to be between 0.26 and 0.27, the RR caused by severe flood events was estimated to be 0.13); Influenza (the RR caused by moderate flood events was estimated to be 0.23, the RR caused by severe flood events was estimated between 0.42 and 0.43). There would be opposite effect of flood event on the following diseases. AHC (the RR caused by moderate flood events was estimated to be 0.35, the RR caused by severe flood events was estimated to be 1.91); Malaria (the RR caused by moderate flood events was estimated to be 0.94, the RR caused by severe flood events was estimated to be 4.38).3. The result of spatial analysis detected that HAV infection is the most sensitive flood related infectious disease (RR=6.62,95%CI:1.19-36.68), and AHC (RR=2.64, 95%CI:1.20-5.83), bacillary and amebic dysentery (RR=2.00,95%CI:1.20-3.34), malaria (RR=4.45,95%CI:1.20-16.41) were also sensitive to flood events. No respiratory infectious disease was identified to be sensitive to flood events.4. In 2020, increased incidence of bacillary and amebic dysentery was estimated to be between 12.93/105 and 23.16/105, HAV infection was estimated to be between 2.04/105 and1 2.11/105, malaria would be 19.89/105, AHC would be-2.4/105. In 2030, increased incidence of bacillary and amebic dysentery was estimated to be between 17.93/105 and 28.28/105, HAV infection was estimated to be between 2.81/105 and 2.90/105, malaria would be 62.8/105, AHC would be 4.97/105.Conclusion:1. Huai River Basin is the flood prone area in Anhui province. In terms of gender, male is the vulnerable population; from age aspect, the low age groups are vulnerable population for most of the intestinal infectious and contact diseases, the middle age group is the vulnerable population for natural focal diseases; the vulnerable population for tuberculosis is high age group while the low age group is the vulnerable population for other respiratory infectious diseases.2. The results from temporal and spatial analysis indicated that, flood events had significant negative effect on bacillary and amebic dysentery, AHC, HAV infection and malaria while mumps may decrease during flood events. Moderate and severe flood events had different impact on diseases, and the effect might be opposite.3. Compared to the baseline condition during 2009 and 2011, bacillary and amebic dysentery, HAV infection and malaria would have significant increased disease burden in the scenarios of 2020 and 2030. AHC may decrease in 2020 and would increase in the scenarios of 2030.Innovation:1. We have proposed the spectrum of sensitive infectious diseases which is related to flood events. All 39 national notifiable infectious diseases were included into the study and classified according to transmission pathway. We have applied same method to all the included infectious diseases in identifying the flood related infectious diseases, which can overcome the differences in the results caused by different included flood events, study areas and methods.2. The combination of descriptive and quantifiable method, temporal (several flood events in different time) and spatial analysis (one typical flood event) were applied in our study. The study has verified that malaria, HAV, AHC and bacillary and amebic dysentery are the flood related sensitive infectious diseases. We also find out that flood events may decrease the incidence risk of respiratory infectious diseases.3. We have classified the flood events into different levels and quantified their effects on diseases respectively. The results showed that different levels of flood events had different effects on diseases. For some diseases, the effects might be opposite.4. With the background of global climate change, we projected the increased disease burden for sensitive infectious diseases under the scenario of population growth and RCP4.5 in 2020 and 2030. The increased frequency and severity of flood events will result in the increasing trend of disease burden for the sensitive infectious diseases in the future.