Quantitative Microbiological Risk Assessment Of Drinking Water In Rural Centralized Water Supply Systems In Mengzi City And Survey Of Diarrhoea Among Schoolchildren Served By The Systems

Objective Small centralized water supply systems are the major form of water supply in rural areas.Compared with urban public centralized water supply systems,there are significant gaps in terms of infrastructure,treatment processes,operation modes and management methods.This water supply system is weak in terms of safety and security of drinking water,and the microorganism is the main cause of water quality,resulting in a certain degree of risk of water-borne diseases among residents in the served area.In this study,the water quality of urban public centralized water supply systems and small rural centralized water supply systems in Mengzi city was tested and analysed,based on the results of microbiological testing,to carry out risk assessment.Meanwhile,a survey was conducted on diarrhoea among schoolchildren to investigate the impact of drinking water quality in rural centralized water supply systems on the health of the population.The results of the study can provide a basis for improving the quality of local drinking water and water safety management,as well as a reference for the prevention and control of diarrhoea in children and adolescents.Methods(1)This study collected drinking water monitoring data(2015 to 2021)for areas covered by urban public centralized water supply systems and small rural centralized water supply systems.The frequency of water sampling and testing is once a month for urban water samples and once a year for rural water samples during the dry season and once during the wet season respectively.The centralized rural water supply system covers eight townships,namely Laozhai Township,Lengquan Township,Mingwu Township,Qilubai Township,Shuitian Township,Xibeile Township,Xin’anshao Township and Zhicun Township.Physico-chemical indicators tested include p H,sulphate,chloride,oxygen consumption,total dissolved solids,total hardness,ammonia nitrogen,anionic synthetic detergents,zinc,aluminium and arsenic,and microbiological indicators include total coliform,total coliforms,heat-resistant coliforms and Escherichia coli.(2)Differences in physical,chemical and microbiological test results and drinking water compliance rates between urban and rural areas were compared.Trends in urban and rural drinking water compliance rates were analyzed.(3)The risk assessment is based on the results of the E.coli tests,and the risk of E.coli infection in the population through drinking tap water is calculated using a beta-binomial distribution model,and the burden of disease caused by E.coli is quantified by calculating disability-adjusted life years(DALYs).10E-04/year and10E-06 DALYs/year were used as risk rubrics,respectively.(4)A stratified random sample was used to select the study population.A self-administered questionnaire was used to investigate students’ diarrhoea and the factors influencing it.(5)Water quality indicators were described using ?X±S.Means were compared using analysis of variance and independent samples t-test.Comparisons of qualification rates were made using the chi-square test.Trends in qualification rates were analysed using Joinpoint regression.Logistic regression was used for analysis of factors influencing diarrhoea.Results(1)A total of 1398 water samples were analysed for testing data.The qualification rates for the physical and chemical indicators of urban and rural finished water were 97.5% and 96.4% respectively(P=0.563).The tap water qualification rates were 95.2% and 97.8% respectively(P=0.047).The overall qualification rate for both urban and rural areas showed an increasing trend(APC=0.69 and APC=0.28).The qualification rates of microbiological indicators for urban and rural finished water were 100% and 62.1% respectively(P<0.01).The qualification rates of tap water were 100% and 74.8% respectively(P<0.01).The qualification rate of microbiological indicators of rural drinking water was on the rise(APC=1.77).(2)The mean values of total coliforms in urban and rural source water were59.03 MPN/100 m L and 47.92 MPN/100 m L respectively(P=0.047),heat-resistant coliforms were 0.29 MPN/100 m L and 7.00 MPN/100 m L respectively(P<0.01)and Escherichia coli were 36.04 MPN/100 m and 10.69 MPN/100 m respectively(P=0.313).MPN/100m(P=0.313);the mean values of total coliforms in urban and rural finished water were 0.00MPN/100 m L and 32.84MPN/100 m L respectively(P<0.01),heat-tolerant coliforms were 0.00MPN/100 m L and 0.42MPN/100 m L respectively(P<0.01),and Escherichia coli were 0.00MPN/100 m and7.14MPN/100 m respectively(P<0.01);the mean values of total coliforms in urban and rural tap water were 0.00MPN/100 m L and 17.67MPN/100 m L respectively(P<0.01),heat-resistant coliforms were 0.00MPN/100 m L and 1.57MPN/100 m L respectively(P<0.01)and 0.00MPN/100 m and 3.34MPN/100 m for Escherichia coli,respectively(P<0.01).(3)The risk of E.coli infection for urban residents drinking tap water is 0 and the DALYs are 0.Rural residents are at risk of E.coli infection in different water periods and townships,specifically in 2019 during the wet water period(5.61E-03),in2020 during the dry water period(5.43E-03)and in the wet water period(3.76E-03);and in different townships,specifically in 2019 in Laozhai Township(risk: 1.65E-02,DALYs: 1.73E-05),Lengquan Township(risk: 9.54E-03)and Mingjiu Township(risk:8.72E-03),and in 2020 Laozhai Township(risk: 1.68E-03),Mingjiu Township(risk:1.11E-02,DALYs: 1.17E-05),and Shuitian Township(risk: 2.68E-02,DALYs:2.81E-05)and Xin’anshao Township(risk: 1.88E-02,DALYs: 1.97E-05),and in 2021 Mingjiu Township(risk: 3.44E-03)and Qilubai Township(risk: 1.92E-03).(4)A total of 1324 students were surveyed for diarrhoea,with an incidence of14%.The number of Escherichia coli in rural drinking water was associated with the occurrence of diarrhoea among students(OR:1.101,P=0.026).Compare to Laozhai Township,students in Xibeile Township had the lowest risk of diarrhoea(OR:0.092,P(27)0.01),followed by Lengquan Township(OR:0.155,P(27)0.01)and Qilubai Township(OR:0.202,P(27)0.01).The risk of diarrhoea was 1.607 times higher among students who had a habit of drinking raw water(OR:0.607,P=0.038)and 1.406 times higher among students who did not drink raw water(OR:0.406,P(27)0.01).The risk of diarrhoea was 5.084 times higher among students who did not wash their hands after defecation than among those who did(OR:5.084,P(27)0.01).Conclusion(1)Compared to urban public centralized water supply systems,small centralized water supply systems in rural areas are less capable of guaranteeing drinking water safety,and microbial contamination of drinking water is the main reason for the impact on water quality.(2)Urban dwellers were not at risk of E.coli infection during the seven-year period and had access to safe drinking water with a high level of security.The rural population is exposed to varying degrees of risk of E.coli infection and has a certain degree of disease burden.(3)The occurrence of diarrhoea in students is associated with the consumption of tap water and there is a certain health risk associated with small centralized water supply systems in rural areas.There is a need to strengthen governance,carry out continuous microbiological monitoring and take measures to reduce microbiological contamination based on risk assessment results to reduce the risk of diarrhoea occurring in the population.In addition,there is a need to strengthen hygiene awareness and good hygiene practices among students.