Reduction of enteric infectious disease in rural China by providing deep-well tap water.

Reduction of enteric infectious disease in rural China by providing deep-well tap water Wang Zeng-sui,P D.S. Shepard,2 Zhu Yun-cheng,3 R.A. Cash,4 Zhao Ren-jie,5 Zhu Zhen-xing,6 & Shen Fu-mi7 Enteric infectious disease (EID), defined here as bacillary dysentery, viral hepatitis A, El Tor cholera, or acute watery diarrhoea, is an important public health problem in most developing countries. This study assessed the impact on EID of providing deep-well tap water (DWTW) through household taps in rural China. For this purpose, we compared the incidence of EID in six study villages (population, 10290) in Qidong County that had DWTW with that in six control villages (population 9397) that had only surface water. Both the bacterial counts and chemical properties of the DWTW met established hygiene standards for drinking water. The incidence of EID in the study region was 38.6% lower than in the control region; however, the introduction of DWTW supplies did not significantly affect the incidence of bacillary dys- entery. These results indicate that the construction and use of DWTW systems with household taps is associated with decreased incidences of El Tor cholera, viral hepatitis A, and acute watery diarrhoea. Since high construction costs have led many authorities to question the value of DWTW, we carriec out a cost-benefit analysis of the programme. The cost of constructing a DWTW system averaged US$ 36000 at 1983 prices, or US$ 10.50 per capita. The combined capital and operating costs of a DWTW system were US$ 1.46 per capita per annum over its 20-year estimated life. The benefits derived from reductions in cost of illness and savings in time to fetch water were 22 times the costs at present values Capital outlays were recouped in a 3.6-year payback period and the provision of DWTW proved highly beneficial in both economic and social terms. Part 1. Evaluation of effectiveness Considerable success has been made in improving health care in China and the life expectancy at birth in the country is now 69 years (18). Environmental improvements, combined with preventive medical measures, have greatly reduced the incidence of com- 1 Associate Professor, Department of Epidemiology, Shanghai Medical University, Shanghai, China. Former Fellow, Takemi Program in International Health, Harvard School of Public Health (HSPH), Boston, MA, USA. 2 Associate Professor, Department of Health Policy and Manage- ment, HSPH, and Research Associate, Harvard Institute for Inter- national Development, One Eliot Street, Cambridge, MA 02138, USA. Requests for reprints should be sent to this address. 3 Director of Monitoring Environmental Sanitation and Water Supply Management, Health and Anti-epidemic Centre, Oidong County, China. 4 Institute Fellow, Harvard Institute for International Develop- ment, and Director of Office of International Health Programs, HSPH, Cambridge, MA, USA. 5 Vice Chief Physician, Health and Anti-epidemic Centre, Jiading County, China. 6 Director of Public Health, Health and Anti-epidemic Centre, Qidong County, China. 7Professor, Department of Epidemiology, Shanghai Medical Uni- versity, Shanghai, China. municable diseases. Nevertheless, enteric infectious disease (EID), defined here as bacillary dysentery, viral hepatitis A, El Tor cholera, or acute watery diarrhoea, remains an important public health problem, especially in rural areas. The major infec- tious agents of diarrhoea are transmitted by the faecal-oral route, often through contaminated water. Several studies (11, 17, 20, 21, 23, 24) have reported that water plays an important role in the transmis- sion of EID in rural China, and some counties in the country have begun to supply deep-well tap wate' (DWTW) to prevent such disease. The primar, purpose of this study was to evaluate the impact o DWTW supplies on the incidence of EID; the result obtained are described below. Materials and methods Shtdy and control regions The study was carried out in 1983 in Qidon- County, which has a population of about 1 million. Six villages (population 10290), where residents had been drinking and using DWTW for 2-3 years, were randomly chosen as the study region. The control region consisted of six other villages (population Bulletin of the World Health Organization, 67 (2): 171-180 (1989) © World Health Organization 1989 171 Wang Zong-sul et al. 9397) that were chosen at random from among the neighbouring villages where residents used surface water (rivers, ditches, etc.). Microbiological and chemical determinations were carried out in 1983 on 24 specimens each of surface water and DWTW. Characteristics of the control and study regions The major difference between the control and study regions at the time of the investigation was the source of drinking water. Inhabitants of both regions had the same kind of natural environment, living conditions, eating habits, and socioeconomic status. As shown in Table 1, the study and control popu- lations had similar age and sex distributions, educa- tion levels, and annual per capita expenditures in the cooperative health system. In 1980, before DWTW was available in the study region, the incidence of EID was similar in the study and control regions. The water is drawn from wells 226-312 metres' deep by hermetically sealed water pumps and piped directly to individual houses or yards. Because the system is sealed, no filtration or chlorination pro- cedures are used. In 1983, 75% of households had tap water available inside the house, while the remainder had the tap in the yard. One tap provided water for 4.3 people on average. Each DWTW system had a permanent staff of one or two to main- tain and operate the supply. Table 1: Selected demographic data for the study and control regions Study region Control region Total population surveyed 10290 9397 % males 47.37 48.09 % in age group: 0-4 years 6.06 5.33 5-14 years 17.80 17.92 15-49 years 57.92 57.94 >50 years 18.21 18.81 % who attended: College or university 0.02 0.04 Middle school 33.27 33.26 Primary school 43.97 43.20 Annual expenditure in the cooperative health system per person (yuan) 5.00 4.90 (USS 1.67) (USS 1.63) Incidence of EID (1980) 280 210 a Per 1000 population per annum. EID = enteric infectious disease. Diagnosis ofEID A rural doctor who was resident in each of the twelve study and control villages recorded in detail all episodes of EID between 1 June and 31 October 1983. The rural doctors saw residents who came to them when they were ill and, in addition, visited the households frequently to ask whether anyone was ill. The doctors used uniform diagnostic standards and case-finding methods. The following definitions of EID were used: diarrhoea-> three liquid stools in 24 hours; dysentery-diarrhoea with blood or mucus and tenesmus, or diarrhoea that was culture-positive for Shigella species; viral hepatitis A-serum glutamic-pyruvic transaminase (or alanine aminotransferase) levels >80 U with clinical symp- toms of fever, malaise, anorexia, nausea, or abdomi- nal discomfort, followed within a few days by jaundice; cholera-diarrhoea with a positive culture for Vibrio cholerae serogroup 01. If required, for diagnosis of dysentery or hepatitis, patients were referred to the hospital for laboratory analysis of blood and faecal specimens. V. cholerae was identi- fied by the Health and Anti-epidemic Centre, Qidong County. The impact of improved water supply was determined from the incidence of EID, calculated as the number of persons who contract such disease divided by the 1982 census population. Results Comparison of the Incidence of EID after the Intervention During the 5 months of the investigation, the overall incidence of EID was 187.2 per 1000 population in the study region and 304.9 in the control region (Table 2). The incidence in the study region was 38.6% below that in the control region, a difference that is highly significant (P < 0.001). The incidence of bacillary dysentery was similar in both regions. No deaths from EID in either region occurred during the observation period. Microbiological and chemical propertles of the water supply The average total bacterial count of the surface water samples from control villages was 3551 per ml, and the average coliform count was 772 per litre. In contrast, in DWTW samples from the study villages the average total bacterial count was 5.4 per ml and the average coliform count was 2.3 per litre. Chemi- cal oxygen demand was 22.1 mg per litre for surface water and 11.0 mg per litre for DWTW samples. Bacterial counts and chemical properties in DWTW met the established hygienic standards for drinking water in China (13) and also the WHO recommend- ed drinking water standards (10).a a Minimum evaluation procedure for water supply and sanitation projects. Unpublished document (WHO/CDD/OPR/83.1). 172 Reduction of enteric Infectious disease In rural China Table 2: Incidence of enteric Infectious disease (EID) In the study and control regions, 1 Jun-31 October 1983 EID Viral hepatitis A Cholera AWD' Dysentery Total Study region: No. of cases 26 1 1816 83 1926 Incidence (per 1000) 2.5 0.1 176.5 8.1 187.2 Control region: No. of cases 88 8 2685 84 2865 Incidence (per 1000) 9.4 0.9 285.7 8.9 304.9 % reduction in study region 73.0 88.2 38.2 - 38.6 Statistical significanceb <0.001 0.02 <0.001 >0.05 <0.001 ' AWD = acute watery diarrhoea. b Results for cholera are based on Fisher's exact test; others based on x2 test. Quantity and reliability of the DWTW supply The DWTW supply facilities functioned contin- uously throughout 1983, and except during power cuts, the quantity of water supplied was sufficient to meet the demands of users. In the summer and early autumn, however, when farm work uses large amounts of electricity, Qidong County had frequent power cuts that interrupted the water supplies. Power was typically switched off for a few hours in late morning and mid-afternoon, and residents then had no alternative but to drink and use polluted surface water. Because each DWTW system had a separate power supply, the lengths of the power cuts and of water disruption varied among the study vil- lages and those with longer cuts had significantly higher (P < 0.001) incidences of acute watery diar- rhoea (Table 3). A regression analysis of these inci- dences on the percentage of time that power was cut indicated that, if the power cuts could be eliminated, the 5-month incidence of diarrhoea in the summer and autumn would drop from 176 per 1000 popu- lation to 17 per 1000, a 90% decline. Table 3: Relationship between the Incidence of acute watery diarrhoea (AWD) and the number of hours of power cuts In villages with deep-well tap water, 1 June- 31 October 1983 No. of cases No. of of AWD Villages hours Population per 1000 Lubei, Ludong 228 (6.2)- 3362 114 Xiangyang, Jinhai 459 (12.5) 4014 174 Yinyang 10, 11b 515 (14.0) 2914 247 Average 401 (10.9) 3430 178 Figures in parentheses are the percentage of 3672 potential hours (153 days x 24 hours). b Variation from expected: X2 = 155, n = 2, P < 0.001. Discussion As noted by Feachem (6), improvements to water supply and sanitation facilities are the most effective interventions for reducing the incidence of diarrhoeal diseases. The degree of impact often depends on the type of water supply. Four factors probably contrib- uted to the effectiveness of DWTW in preventing EID in the present study. First, the improvement of water quality reduced the load of waterborne patho- gens. Second, the increased access to water, i.e., a piped supply in the home, reduced the use of pol- luted sources and the opportunity for contaminating portable water. Third, when water is available in the house, it is more likely to be used for general sani- tation and personal hygiene. Finally, the population liked the appearance and taste of the water, so that there was no disincentive to consuming it. The results of the study indicate that drinking DWTW was associated with the reduction in inci- dence of viral hepatitis A, cholera, and acute watery diarrhoea; however, provision of such water did not seem to influence the incidence of bacillary dys- entery. Esrey et al. (3) have indicated that in poor communities a limited improvement in water supply and sanitation facilities can have a greater impact on diarrhoea caused by pathogens that have a high infective dose than on diarrhoea caused by patho- gens that have a low infective dose, e.g., Shigella spp. As noted above, the availability of DWTW apparently reduced the incidence of EID by 38.6%. There are several reasons why the reduction was not greater. First, during the power cuts, the inhabitants in the study villages often used polluted surface water. Second, intestinal pathogens are not only spread by water (the role of water in the transmis- sion of campylobacter and rotavirus has not been well defined). In the study only the impact of drink- ing relatively safe deep-well water was measured; public health measures such as personal and domes- 173 Wang Zeng-sul et al. tic hygiene and the management of excreta were not investigated in connection with the introduction of DWTW. Third, the residents of Qidong County have traditionally eaten raw seafood (such as snails, shrimps, crabs, and clams) that is processed with salt and vinegar. Any of these foodstuffs could also trans- mit EID. We assume that the incidence of diarrhoeal illness and EID will be further reduced when the problems mentioned above are solved. Improving water supplies is not only a means of preventing enteric infectious diseases, but also a way of improving other aspects of health. The entire population in the study region is now reaping the health benefits of a better water supply and this will inevitably increase their social well-being. Part 2. Cost-benefit analysis As shown in part 1 of this article, provision of DWTW systems is an effective and feasible way of reducing the incidence of EID. The annual mortality from liver cell cancer was also lower among persons who had used DWTW for at least 10 years (15, 16, 22, 25, and Zhao Ren-jie et al., unpublished results, 1986). DWTW has been used in some villages in Qidong County since the mid-1970s. However, because the construction costs of such systems are high in relation to county health and environmental budgets, many counties and public health agencies question these investments. In view of the scarcity of resources, a precise understanding of the health benefits and costs of water supply is therefore criti- cal. We collected detailed information on com- munity and individual expenditures for the construc- tion and operation of DWTW systems and on EID in Qidong County. As far as we are aware, this is the first cost-benefit study of the provision of DWTW supplies with household taps for the prevention of EID in China. Materials and methods The costs and benefits of DWTW were calculated using methods described by Shepard et al. (14),b Reynolds & Gaspari (12), and Hsiao (8). For this purpose, we took the project life to be the 20-year useful life of the buildings. b Shepard, D.S. et al. The cost of an oral rehydration therapy programme: a manual for managers. Institute for Health Research, Harvard School of Public Health, 1985 (prepared for the WHO Control of Diarrhoeal Diseases Programme). Costs of the DWTWprogramme The DWTW systems were built by Qidong County's well-making team and each of the three systems con- structed serves two villages, each of about 1715 people. The programme incurs both capital and recurrent (operating and maintenance) costs. Capital costs include the material and manpower used by the team to drill the well, and the cost of buildings, land, and equipment such as machines, water towers, downpipes, and water taps for each household. Recurrent costs include expenditure on upkeep (or repair), charges for electricity, and the wages of the programme administrator. A useful life of 10 years was taken for the equipment (4). We assumed that investment costs were incurred at the beginning of each investment year because of the time taken for construction and installation, and that recurrent costs were incurred at the end of each project year. Costs were determined in yuan for the study year (1983) and an exchange rate of US$ 1.00 = 3.3 yuan was used. All costs were converted to present value at a real interest rate of 5%, as shown in Table 4. Costs of Illness The costs of illness include both direct and indirect components. Direct costs involve expenditures for treatment and containment of EID; for example, expenditures on hospitalization, medical treatment and medicine, transportation of patients, laboratory examinations, isolation and disinfection, salaries and fringe benefits of health personnel, and rural doctors' salaries. Patients who were hospitalized with EID were treated by EID doctors and nurses, and so the entire salaries of these health-care providers were attributed to these cases. The salaries of rural doctors were allocated to EID depending on the proportion of visits to clinics made by patients with such diseases.c This proportion was calculated from the register that listed patients by diagnosis, which was maintained by all the rural clinics covered in the study. As indirect costs were included the lost wages or earnings of patients and of their relatives who looked after them during their illness; here, data were obtained from a household survey and from examination of the patients' hospital records. Economic analysis The affordability of the DWTW programme was assessed by the initial capital cost per capita and the annualized total cost per capita. Annualized costs were calculated by dividing the relevant present value cost by the annualizing factor (12.46), whose c See footnote b. 174 Reduction of enteric Infectious disease In rural China Table 4: Costs and benefits of deep-well tap water (DWTW) In the study region Cost ( x 1000 yuan) Incurred Present With one DWTW Study during value system region years: (x 1000 yuan) Capital costs: Drilling well 19.0 57.0 1' 57.0 Buildings (water tower, engine room) 21.5 64.5 1' 64.5 Equipment 78.2 234.6 1, 11 378.6 Subtotal 118.7 356.1 500.1 Recurrent costs: Electricity 2.0 6.0 1-20 74.8 Administrators' wages 0.9 2.8 1-20 34.4 Equipment upkeep 0.2 0.6 1-20 7.5 Subtotal 3.1 9.4 1-20 116.7 Total costs 616.8 Benefits: Averted costs of EIDb 60.6 1-20 754.9 Time saved in water collection 47.2 1-20 587.9 Total benefits 107.8 1-20 1342.8 a Cost incurred at beginning, rather than end, of the years indicated. b EID = enteric infectious disease. magnitude is determined by the project life and the interest rate. Economic costs were expressed on both a gross (ignoring revenues from water users) and net basis (including such revenues). The cost-benefit analysis related the total cost of the programme to the savings in the cost of illness and in the time spent in collecting water. The gross benefit-cost ratio was defined as benefits divided by costs (2). Results Costs of the DWTW system The cost at present value of constructing and oper- ating DWTW systems for the study region over 20 years was estimated to be 616 800 yuan (Table 4). Capital costs account for 81% of this total. The initial capital cost of one DWTW system (118 700 yuan = US$ 36 000) is equivalent to 34.61 yuan (US$ 10.50) per capita, or about 24 days' wages for an average worker in China. The annualized per capita cost of the project is 4.81 yuan, which represents about 3 days' wages. Each resident of the study region (10290 in 1983) paid water rates of 0.10 yuan per month. The resulting annual income of 12348 yuan exceeds the recurrent costs (9400 yuan per annum), and hence the system operates at a recur- rent surplus. This surplus is not large enough, however, to amortize the initial capital investment or to replace the equipment after 10 years. Costs of avoided Illness Table 5 shows the average costs of EID per case according to the type of illness. All patients with EID, details of which were recorded by rural doctors, were treated. Those with El Tor cholera were isolated at home and thus incurred no hospital- ization costs. Because the incidence of bacillary dys- entery was similar in the study and the control regions, this disease was excluded from our analysis. The costs of supplemental nutrition and the value of gifts sent by the patient's relatives to assist towards their recuperation were as large as the expenditure on treatment and medicine, together representing 26% and 48% of the overall direct costs for cholera and hepatitis, respectively. For cholera and diar- rhoea, indirect costs exceeded direct costs. The overall incidence of EID in 5 months was 187.2 per 1000 population in the study region and 304.9 per 1000 in the control region. Epidemiological investigations suggest that, in the control region, inhabitants who used surface water that was pol- luted had a higher incidence of cholera, viral hepa- titis A, and acute watery diarrhoea than those who 175 Wang Zeng-sul et al. Table 5: Average cost per case of enteric Infectious disease (EID)" Cost (yuan) Viral hepatitis Cholera Diarrhoea Direct costs: Hospitalization 8.40 (1.8)b Treatment and medicine 150.20 (31.8) 30.00 (12-9) 1.00 (23.3) Laboratories 6.40 (1.4) 6.50 (2.8) Supplemental nutrition and sending presents 167.50 (35.4) 30.00 (12.9) Disinfecting premises 4.24 (0.9) 3.00 (1.3) Salaries and fringe benefits of health personnel 7.20 (1.5) 33.51 (14.4) 0.15 (3.5) Wages of rural doctor 0.30 (0.1) 0.30 (0.1) 0.30 (7.0) Transportation 5.00 (1.1) 6.80 (2.9) Chemoprophylaxis 3.57 (1.5) Subtotal 349.24 (73.9) 113.68 (48.8) 1.45 (33.8) Indirect costs: Lost earnings of patients and their relatives 123.54 (26.1) 119.28 (51.2) 2.84 (66.2) Total 472.78 (100) 232.96 (100) 4.29 (100) All cases of EID were treated. b Figures in parentheses are percentages of total costs. used DWTW supplies-the incidence of cholera, annual number. A total of 1846 cases of presumed viral hepatitis A and acute watery diarrhoea in the EID were averted per annum in the study popu- study region being reduced by 88.2%, 73.0%, and lation as a result of using DWTW supplies (Table 6). 38.2%, respectively. These cases constitute a 38.6% reduction in the Cases of diarrhoea and hepatitis occur through- overall incidence of EID since the programme began. out the year in Qidong County, but are most Acute watery diarrhoea accounted for 94% of the common from June to October. An estimate of the EID cases. If the attack rate of EID remains con- number of cases of EID that were averted per stant in the coming years, the predicted total annum among DWTW users in the study region was avoided expenditure on illness, i.e., the direct eco- obtained by extrapolating from the 5-month study nomic benefit attributable to using DWTW supplies, period using the relationship: will be 60 578 yuan per annum. No. of cases averted = (No. expected) -(No. found) Time saved In fetching water % of cases from June to October The installation of a convenient village water supply system greatly reduced the time spent in carrying where the expected number of cases was expressed as water, as has been reported previously in many the incidence in the control region multiplied by the countries (1, 5, 7). Without a running supply, house- population in the study region. hold members would have had to make three trips We assume that the number of cases of acute each day to carry water for people and livestock watery diarrhoea and viral hepatitis A in the study from rivers or ditches situated 10-40 metres away period represent 65% of the annual number and that from their houses. The time devoted to collecting the cholera cases represent 90% of the respective this water was estimated from a small survey in the Table 6: Annualized costs of Illnesses that were averted by using deep-well tap water In the study region Viral hepatitis A Cholera Diarrhoea Total Cost of illness per case (yuan) 472.78 232.96 4.29 No. of cases averted per annum 108.2' 8.6 1729.5 1846.3 Total savings (yuan) 51154.80 2003.46 7419.56 60577.8 Estimated as ((0.936% x 10290) - 26)/65% = 108.2 176 Reduction of enteric Infectious disease In rural China control village to average 20 minutes per household per day. There were 3165 households in the study region, and the average daily wage in Qidong County was 1.47 yuan. A working day was conserva- tively estimated to be 12 hours, and hence the hourly wage was at least 0.1225 yuan. Thus, in terms of time saved alone, the availability of tapped water directly in households in the study region amounted to 47 172 yuan per annum (3165 households in the study region x 20/60 hour per day x 365 days per year x 0.1225 yuan per hour). Additional benefits Qidong County is hyperendemic for liver cell cancer (mortality rate, approximately 50 per 100000). Su De-long, who studied the possible factors and causes of the hyperendemicity rates in the region, suggested that this cancer may be associated with drinking stagnant or ditch water (15); the installation of DWTW in 1977 reduced the mortality from liver cancer in the region (Zhao Ren-jie et al., unpublished results, 1986). Estimates indicate that after 10 years of DWTW, the incidence of liver cancer in the study region might be reduced by five cases per annum. An average case of liver cell cancer costs about 5515 yuan for medical treatment and entails about 15-20 years of lost wages from premature death (Zhao Ren-jie et al., unpublished results, 1986). Potentially, DWTW systems could result in an annual saving of about 27575 yuan for costs associated with liver cancer after 10 years (or 130700 yuan at present value). Since, however, a causal link between liver cancer and drinking stagnant or ditch water has not been confirmed, these benefits were not included in the study. Use of DWTW can also help to control other water-related conditions, such as skin and eye infec- tions, dermatosis, gynaecological conditions, para- sitic enteric diseases, as well as vector-borne diseases (5, 9). Also, a DWTW supply has many intangible benefits. For example, many of the residents who were interviewed praised the convenience and sim- plicity of the running water system and noted that provision of the service was one of the first improve- ments made by the county government to their rural area and that it will benefit future generations. In addition, industry and agriculture are already pro- fiting from the DWTW supply. None of these bene- fits were, however, included in the analysis. Cost-enefit analysis Table 7 presents the results of a cost-benefit analysis of the DWTW project from a societal viewpoint. Overall, the net benefits were positive and were 2.2 times the costs. If the benefits of reduced liver cancer Table 7: Results of the cost-benefit analysis of the avail- ability of deep-well tap water In the stdy region Net Benefits Costs benefits Total, present value ( x 1000 yuan) 1342.8 616.8 726.0 Total, annualized ( x 1000 yuan) 107.7 49.5 58.3 Per capita, annualized (yuan) 10.47 4.81 5.66 (3.17)' (1.46) (1.72) 8 Figures in parentheses are US$. were causally related to DWTW, the benefit-cost ratio would rise to 2.4. The user fees paid by residents are only about a quarter of the benefits they derive from either the costs of avoided illness or in time savings, and the right to use DWTW is there- fore valuable from the users' viewpoint. Economic loss due to power cuts As indicated in part 1 of this article, Qidong County has frequent power cuts that reduce water supplies in the summer and early autumn when farm work requires large amounts of electricity. About 90% of the cases of diarrhoea could, however, be averted if interruptions to water supply could be eliminated. Since currently the expenditure per case of diarrhoea amounts to 4.29 yuan, such interruptions cost 2348 yuan per annum in the study region. Discussion The Alma-Ata Declaration urged that primary health care include the provision of adequate supplies of safe water and basic sanitation (19). Stimulated by the International Drinking Water Supply and Sanitation Decade (1981-90), China is making great efforts to improve water supplies in both urban and rural areas. The experience of Qidong County that we have reported has shown that local governments and health bureaux can make a contribution by providing a DWTW supply. Such systems can improve the quality of and increase the availability of water, so that more can be used for general sanitation and personal hygiene. As we have shown, DWTW appears to reduce the incidence of cholera, viral hepatitis A, and acute watery diarrhoea. In order to offset the power shortages in Qidong County, which frequently resulted in water supplies being cut off in summer and early autumn, it may be useful for DWTW systems to install larger water towers or back-up generators, or to switch heavy uses of power, e.g., pumping of water for irri- 177 Wang Zeng-sul et al. gation, to off-peak times to avoid interruptions in the water supply. In Qidong County, the initial con- struction cost per capita of the DWTW system was 34.61 yuan (US$ 10.50), and the per capita annu- alized cost was 4.81 yuan (US$ 1.46). These costs are 83% below those cited by WHO, which reported initial construction costs of US$ 60 per capita (median value) and an annual cost of US$ 10 per capita for water systems in 87 developing countries (3). Sensitivity analysis of the results indicates that discount rates from 2% to 10% do not affect our conclusions significantly. There are a variety of possible explanations for the lower costs of providing DWTW in China. First, the equipment (machines, pumps, pipes, etc.) is all manufactured internally; in contrast, in other developing countries the majority of such equipment is imported from developed countries. Second, expa- triate technician assistance is not needed in China, and the local labour rates are low. Third, one or two permanent employees were assigned to maintain and operate each DWTW system, thus ensuring local expertise to repair machines and pumps, should they malfunction. A favourable benefit-cost ratio of 2.2 for invest- ment in DWTW systems was found. The social bene- fits complement the economic benefits of reduced morbidity and of time saved. The DWTW supply has proved its effectiveness and feasibility in Qidong County and is widely accepted there; by the end of 1985, 57% of the county's population used such water supplies, a considerable increase from the 27% at the end of 1983. The experience of the inhabitants of Qidong County that we have reported here should apply to comparable rural areas elsewhere in the world, and a DWTW programme is likely to be worthwhile wherever inhabitants are currently relying on con- taminated surface water. A high population density makes feasible the supply of piped water to house- holds. Also, in countries that have enough skilled manpower and are sufficiently developed industrially to permit the construction and maintenance of a DWTW system with local resources, the cost of such systems should be relatively low. We believe that many areas of China and other countries would realize benefits as favourable as those in Qidong County. Acknowledgements We would like to express our deep appreciation to Pro- fessor Su De-long, Professor Yu Shun-zhang, Professor Yuan Hong-chang, Professor David E. Bell, Professor L.C.H. Chen, Dr V. Ramalingaswami, and Professor Michael R. Reich for their helpful comments and reviews. We would like to extend our gratitude to our students, Miss Zhang Hui and Miss Zhang Ping, for their support and assistance in the study. We also thank Mrs Zhou Ming-e, Mrs Lin Yu-zun, Mrs Laurie Shepard, Dr Yu Guo- pei, Mr Jim Cashel, and Miss Ann Gardner for their assistance. Resume Reduction des enterites infectieuses en Chine rurale grace a I'adduction d'eau provenant de puits profonds Cette etude examine l'efficacite de l'adduction d'eau provenant de puits profonds dans la lutte contre les enterites infectieuses dans les cam- pagnes chinoises et en propose une analyse cout- avantages. Les enterites infectieuses dont il s'agit sont le cholera el tor, la dysenterie bacillaire, I'hepatite A et la diarrhee aqueuse aigue. Les re- seaux de distribution d'eau provenant de puits profonds ont ete realises par l'equipe de puisa- tiers de la region de Qidong. Des pompes herme- tiques puisent l'eau entre 226 et 312 m de profondeur et l'amenent directement a l'interieur des habitations ou dans la cour. II n'y a ni fil- tration, ni chloration, etant donne que l'adduction s'effectue dans un systeme hermetiquement ferme. Une etude epidemiologique a ete realis6e dans 12 villages, totalisant 19687 habitants, de la region de Qidong afin de determiner dans quelle mesure l'etablissement de reseaux distribuant l'eau provenant de puits profonds jusque dans les foyers pouvait interrompre la transmission des enterites infectieuses. L'etude epidemiologique a porte sur la periode du ier juin au 31 octobre 1983. Le canton etudie comprenait six villages de la region de Qidong choisis au hasard, totalisant 10290 habitants et pourvus de reseaux d'adduction d'eau potable et a usage menager depuis deux ou trois ans. Le canton temoin r6unissait six villages avoisinants, totalisant 9937 habitants, dont les resi- dents consommaient des eaux de surface non trai- tees. Les habitants des deux cantons jouissaient du meme environnement naturel et avaient le mmrne genre de conditions de vie, d'habitudes ali- mentaires et de statut socio-economique. En 1980, epoque ou les habitants des deux cantons con- sommaient de l'eau de surface, l'incidence des enterites infectieuses etait similaire. EffIcacIt du programme Les comptages bacteriens et l'analyse chimique de l'eau de distribution correspondaient aux cri- 178 Reduction of enteric Infectious disease In rural China teres hygieniques normaux de 1'eau potable. L'incidence des enterites infectieuses dans le canton 6tudi6 (187 cas par mille habitants) 6tait de 38,6% inferieure au taux constate dans le canton temoin (304 cas par mille habitants), soit une diffe- rence hautement significative (P < 0,001). Les effets de I'adduction d'eau sur l'incidence de la diarrhee n'etaient pas lies a I'age. L'etablissement de r6seaux d'adduction d'eau provenant de puits profonds n'a pas eu d'effets significatifs sur l'incidence de la dysenterie bacillaire mais s'est accompagne d'une diminution de l'incidence du cholera el tor, de l'hepatite A et de la diarrh6e aqueuse aigue. Evaluation des couts CoOt des r6seaux de distribution. Le cout en capital de la construction d'un reseau de distribution d'eau provenant de puits profonds desservant 3430 per- sonnes a ete en moyenne de US$36000 (118700 Y), soit US$10,50 par tete. Les depenses renou- velables annuelles se sont eleveos a 946 dollars (3120 Y) par reseau, soit 0,27 dollar par tete. Chaque menage desservi a paye une redevance de 0,36 dollar (1,20 Y) par an. La recette annuelle apportee par les redevances des utilisateurs, soit 1247 dollars (4120 Y), depassait les frais renouve- lables. En d'autre termes, si l'on ne tient pas compte de l'amortissement, le reseau produit un excedent r6gulier. Trois reseaux ont ete neces- saires pour desservir la totalite de l'aire 6tudi6e (un reseau pour deux villages). CoOls dus aux maladies. Le cout economique moyen par cas, comprenant le traitement, le transport et la perte de gain des patients et de leur famille, s'61eve a 143 dollars pour l'hepatite A, 40 dollars pour le cholera et 1,30 dollar pour la diarrhee aqueuse aigue. L'adduction d'eau potable pro- venant de puits profonds a permis d'eviter chaque annee dans le canton etudie un total de 1846 cas presum6s d'enterites infectieuses. Le cout total de la morbidite par enterites infectieuses qui a pu ainsi etre evit6e dans le canton etudie atteint 18357 dollars (60580 Y) par annee. Economle de temps sur I'approvislonnement en eau. Le temps utilise quotidiennement pour I'approv- isionnement en eau etait en moyenne, dans le canton t6moin, de 20 min par menage. Le gain de temps resultant de l'adduction directe de l'eau aux logements a donc pu 6tre evalue a 14300 dollars (47 170 Y) par an sur la base des salaires releves en 1983. D'autres enqu6teurs ont constate que l'incidence du carcinome hepato-cellulaire etait moindre dans les cantons de la region de Qidong qui disposent de reseaux d'adduction d'eau pro- venant de puits profonds depuis plus de dix ans. S'il y a bien relation de causalite entre les deux faits, le canton etudie aura economise en outre 39610 dollars (130700 Y) en frais de traitement sur 20 ans. Analyse economique Analyse coOt-advantages. Tous les couts et avan- tages ont ete actualises sur 20 ans au taux de 5%, 20 annees representant la duree de vie utile des constructions et du puits. La duree de vie utile du materiel etant de 10 ans, la valeur actualisee com- prend le remplacement de tout le materiel au cours de la onzieme annee. Dans 1'ensemble, les avantages economiques des reseaux d'adduction d'eau provenant de puits profonds sont egaux a 2,2 fois leur coOt. Les redevances payees par les utilisateurs correspondent a un quart seulement des avantages que le systeme leur procure. Si l'on tient compte du cancer du foie dans I'analyse, le rapport coOt-avantages s'6l1ve a 2,4. Pertes Oconomiques dues aux coupures de courant. En ete, et au debut de l'automme, lorsque les travaux agricoles necessitent d'importantes quantites d'electricite, la region de Qidong souffre de fre- quentes coupures d'electricite qui interrompent I'alimentation en eau. Plus les coupures d'electricite se prolongent, plus l'incidence de la diarrhee aqueuse aigue est elevee. Une analyse des donnees par regression lineaire montre que 90% des cas de diarrhee aqueuse aigue pour- raient etre evites si l'on pouvait eviter toute inter- ruption dans la distribution d'eau. Les differentes strategies utilisables a cet effet comprennent l'installation et l'entretien de reservoirs de stockage de plus grande capacite, de genera- teurs de secours, ou la reduction pendant les pe- riodes de pointe de la consommation d'electricite a d'autres fins. Les depenses courantes s'elevant a US$ 1,30 par cas de diarrhee aqueuse aigue, il serait justifi6 de depenser un supplement de US$ 712 par an et par reseau d'adduction si l'on pouvait a ce prix 6liminer les interruptions de dis- tribution. Le coOt par tete d'un reseau d'adduction d'eau, qui s'el6ve a US$ 1,46 sur une base annualisee, est d'environ 83% inferieur au coOt des reseaux evalues par l'OMS dans 87 pays en d6veloppe- ment. Ce faible cout est probablement dO a plu- sieurs facteurs. La Chine a ete capable de fabriquer elle-meme les pompes et le materiel necessaire; des equipes locales ont pu concevoir et installer tous les reseaux sans assistance tech- 179 Wang Zeng-sul et al. nique ext6rieure; des agents locaux permanents, employes a plein temps, ont ete affectes a l'entretien et 'a 'exploitation de chaque r6seau, de sorte que l'on pouvait disposer pour les repara- tions d'un savoir-faire local d'un cout modique. Un programme d'adduction d'eau provenant de puits profonds est de nature a ameliorer la sante partout ou la population doit actuellement se con- tenter d'eau de surface contamin6e et utiliserait exclusivement de l'eau de distribution provenant de puits profonds si elle en disposait. 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