Interventions for the control of diarrhoeal diseases among young children: improving water supplies and excreta disposal facilities*

Bulletin ofthe WorldHealth Organization, 63 (4): 757-772 (1985) © World Health Organization 1985 Interventions for the control of diarrhoeal diseases among young children: improving water supplies and excreta disposal facilities* S. A. ESREY,' R. G. FEACHEM,2 & J. M. HUGHES3 A theoretical model isproposed that relates the level of ingestion ofdiarrhoea-causing pathogens to thefrequency ofdiarrhoea in the community. The implications of this model are that, in poor communities with inadequate water supply and excreta disposal, reducing the level of enteric pathogen ingestion by a given amount will have a greater impact on diarrhoea mortality rates than on morbidity rates, a greater impact on the incidence rate of severe diarrhoea than on that of mild diarrhoea, and a greater impact on diarrhoea caused by pathogens having high infectious doses than on diarrhoea caused by pathogens ofa low infectious dose. The impact ofwater supply and sanitation on diarrhoea, related infections, nutritional status, and mortality is analysed by reviewing 67 studiesfrom 28 countries. The median reductions in diarrhoea morbidity rates are 22% from all studies and 27% from a few better-designed studies. All studies ofthe impact on total mortality ratesshow a median reduction of21%, while thefew better-designed studies give a median reduction of30%. Improvements in water quality have less of an impact than improvements in water availability or excreta disposal. Of the several interventions that may reduce diarrhoea morbidity and mortality rates (38), the improvement of water supply and excreta disposal facilities has attracted particular interest. These environmental improvements, together with improvements in living standards, played a major role in reducing diarrhoea rates and controlling epidemic typhoid and cholera in Europe and North America between 1860 and 1920. It is anticipated that the improvement of water supply and excreta disposal in poor communities in developing countries today will have a substantial impact on diarrhoea morbidity and mortality rates in those communities. This expectation provides part of the motivation for the International Drinking Water Supply and Sani- tation Decade (1981-1990), the aims of which are to increase the rate at which new water supply and excreta disposal facilities are constructed and to maxi- mize the probability that they will be correctly opera- * Requests for reprints should be sent to the Director, Diarrhoeal Diseases Control Programme, World Health Organization, 1211 Geneva 27, Switzerland. ' Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853, USA. 2 Head, Department of Tropical Hygiene, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, England. 3 Director, Hospital Infections Program, Center for Infectious Diseases, Centers for Disease Control, Public Health Service, US Department of Health and Human Services, Atlanta, GA 30333, USA. ted, maintained and used. The potential impacts of improved water supply and excreta disposal on diarrhoea and other water- related diseases in developing countries have been discussed and debated at length over the past decade. White et al. (86) provided a conceptual framework for the debate in the context of studies in East Africa; McJunkin (56) reviewed the topic extensively; Saunders & Warford (70) summarized the water supply impact studies; Feachem et al. (39) summarized the excreta disposal impact studies; and Blum & Feachem (13) and Esrey & Habicht (28) considered the methodological difficulties inherent in attempts to measure the impact of water supply and excreta disposal projects on diarrhoea. In this review we analyse the effectiveness of water supply and excreta disposal improvements for reducing diarrhoea rates in young children in developing countries. We also examine their impact on diarrhoea-related infections, nutritional status, and mortality. We make no attempt to analyse other impacts of water supply and excreta disposal improvements or to compute an overall cost-benefit ratio for these investments. This paper is the ninth in a series of reviews of potential anti-diarrhoea inter- ventions (2, 25, 26, 32, 34-36, 38).a aASHWORTH, A. & FEACHEM, R. G. Interventions for the control of diarrhoeal diseases among young children: improving lactation. Unpublished WHO document CDD/85.2, 1985. 4581 -757- S. A. ESREY ET AL. EFFECTIVENESS For improved water supply or excreta disposal facilities to be an effective diarrhoea control intervention, it must be true that: either water supply or excreta disposal improvements can reduce the inges- tion by young children of pathogens causing diarrhoea hypothesis and a reduction in the ingestion of these pathogens by young children can reduce diarrhoea morbidity or mortality rates hypothesis 2 or water supply or excreta disposal improvements can reduce diarrhoea morbidity or mortality rates among young children hypothesis 3 The effectiveness of improved water supply and excreta disposal would be suggested by a demonstra- tion either of the correctness of hypotheses 1 and 2 or the correctness of hypothesis 3. In some other reviews in this series (for instance, 35, 36), most of the literature bears on hypotheses 1 and 2, and hypothesis 3 must be handled by theoretical calculations. Here the reverse is the case: there are few data on hypotheses 1 and 2 and an extensive literature on hypothesis 3. The evidence for and against the three hypotheses is examined below. Hypothesis 1. Water supply or excreta disposal improvements can reduce the ingestion by young children ofpathogens causing diarrhoea. There is some evidence to suggest that three types of water and excreta disposal improvements (improved water quality, increased water availability and quantity associated with better hygiene practices, and improved excreta disposal facilities) may reduce the ingestion of pathogens causing diarrhoea (33). All the major infectious agents of diarrhoea are transmitted by the faecal-oral route, and all can be transmitted via contaminated water. For most agents water-borne transmission has been documented. For some agents there is good evidence that, at least in some places at some times, water is a major vehicle of transmission. Notable examples are Salmonella typhi, Vibrio cholerae, and Giardia lamblia (39). Traditional water sources are often highly con- taminated with faecal matter. Improved water sources may be free of contamination or considerably less contaminated than unimproved water sources (30, 77). Uncontaminated source water may become polluted by the time it is ingested, and water storage in home containers may result in increased con- tamination depending on storage conditions (37, 66, 72). Increased water availability and quantity, associated with improved hygiene, may reduce faecal contamination of the hands. Proper cleaning of utensils, food, and home environments is also likely to reduce transmission of faecal matter. The transmission of all the main diarrhoea-causing agents is probably influenced to some degree by increased water availability and quantity, but it is Shigella transmission that has been particularly associated with poor personal and domestic hygiene (45, 78). This may be because of the low infectious dose of Shigella relative to other bacterial enteric pathogens, or it may be only because Shigella has been most studied. The relationship between personal hygiene and the newly-recognized diarrhoea agents (especially Campylobacter jejuni, enterotoxigenic Escherichia coli, and rotavirus) should be studied. All the major infectious agents of diarrhoea are shed by infected persons via the faeces, and therefore hygienic disposal of human excreta plays a role in controlling them. Use of toilets by all members of the community should reduce faecal contamination of houses, yards and gardens, and the neighbourhood. In addition, proper treatment and disposal of human excreta would prevent faecal contamination of fields, crops, and receiving water-bodies, which would in turn further reduce the transmission of faecal pathogens. The hygienic disposal of the faeces of children too young to use the toilet is of the utmost importance, because such children constitute an important reservoir of several agents of diarrhoea (for instance, rotavirus and enterotoxigenic E. coli). Hypothesis 2. A reduction in the ingestion of these pathogens by young children can reduce diarrhoea morbidity or mortality rates. The ingested dose of a pathogen required to cause diarrhoea depends upon the particular properties of the pathogen and upon a number of host factors. The general relationship between ingested dose and proportion of exposed persons contracting diarrhoea . . 758 IMPROVING WATER SUPPLIES AND EXCRETA DISPOSAL FOR CONTROL OF DIARRHOEAL DISEASES 759 100 _ I ~~~/,Ex / (LI mo / He i A0_-SCL .~0/ 00 A ID5 BLow High Dose of pathogen X ingested by all persons Fig. 1. Dose-response relationship for a group of susceptible persons, all exposed to an equal dose of pathogen X. is shown in Fig. 1. In the dose range below A, no one becomes ill.? In the dose range above B, all susceptible persons develop diarrhoea. Between A and B lies an intermediate range in which some persons become ill and others do not. The dose at which 507o of challenged persons become ill is known as the median infectious dose (ID50), which is the figure generally reported from volunteer studies. Little is known about the shape of the curve in the intermediate range and, for this reason, a broken line is shown in Fig. 1. Both the shape of the curve and the values of A, B, and the IDso depend upon the particular pathogen, its method of ingestion (in water or in food), and a variety of features of the exposed group of people, such as age and immunity. Available ID50 and other infectious dose data have been recently reviewed for all the major diarrhoea- causing pathogens (39). For bacterial agents there is a wide range of ID50 values-from around 103 for Shigella to 10'-10" for Vibrio cholerae. Less is known about the viral and protozoal agents of diarrhoea, although there are grounds for assuming that the ID50 values are relatively low (< 102 ). Nearly all infectious dose data are derived from studies on volunteers in which the subjects were healthy adults from developed countries. The doses necessary to infect children, particularly malnourished children, may be very different. ID5o values also depend on the food or drink with which the pathogens are ingested; therefore, they may differ among countries with differing dietary and child-feeding practices. In h Despite the representation in Fig. 1, it may be that for some pathogens A = 0. High .1~ ~ ~ 0 Lowel A a C D E F Dow of entbric ptsogmw gno P High Fig. 2. Dose-response relationship for young children under various levels of exposure to an array of enteric pathogens. addition, in situations where large numbers of persons are exposed to diarrhoea-causing pathogens, the ID, or IDo., values may be of greater epidemiological relevance than the 1D50 values. More reliance can be placed on the relative ranking of pathogens by ID50 than on the absolute dose values obtained from studies on volunteers. The relationship depicted in Fig. 1 may be generalized to a group of young children having different levels of water supply and excreta disposal services and, consequently, different levels of ingestion of enteric pathogens (Fig. 2). Consider first the incidence rate of mild diarrhoea. At low levels of ingestion (A-B), there remains an appreciable incidence of mild diarrhoea, made up of an irreducible minimum of infectious diarrhoea, plus diarrhoea not due to enteric pathogens. This situation is exemplified by children in wealthy communities in developed countries. When ingestion rises above point B, the incidence rate of mild diarrhoea also rises. At point D saturation is reached, and further increases in the ingestion of pathogens do not result in an increased incidence rate of mild diarrhoea. As in Fig. 1, the shape of the curve between points B and D on the "mild diarrhoea incidence" line in Fig. 2 is unknown, so a broken line is shown. Poor com- munities in developed and developing countries, with their elevated diarrhoea incidence rates, clearly lie to the right of point B. The incidence rate of severe diarrhoea, which may be defined by stooling rate, stool volume, duration, degree of dehydration or other measures, is indicated on Fig. 2 by the distance between the two lines (the shaded band). The incidence rate of severe diarrhoea is less than that of mild diarrhoea, but it represents an increasing proportion of the total diarrhoea incidence rate as the ingestion of enteric pathogens rises above 760 S. A. ESREY ET AL. the level represented by point C.c The incidence rate of severe diarrhoea is shown in Fig. 2 to be constant in the range A-C, to rise in the range C-E, and to be constant in the range E-F. The breakpoints for severe diarrhoea incidence rate (C and E) are offset to the right of the equivalent points for mild diarrhoea inci- dence rate (B and D), on the assumption that for a single pathogen a higher ingested dose is necessary to produce severe diarrhoea than mild diarrhoea. There is direct experimental confirmation of this for entero- toxigenic E. coli (27) and for Vibrio cholerae (19). Indirect evidence is also available for Salmonella, for which there is an inverse relationship between dose and incubation period (12) and an inverse rela- tionship between incubation period and severity (10). Fig. 2 assumes that the ID5o for severe symptoms is higher than the ID5o for mild symptoms for most enteric pathogens. The model put forward in Fig. 2 is tentative and grossly simplified. It may be more applicable to young children than to a whole community. The complex role of immunity is not specifically addressed in the model and, for certain pathogens, the improvement of hygienic conditions may lead to an increase in diarrhoea incidence rates in older age groups. A more complete modelling of the interrelationships between hygiene levels and diarrhoea incidence is difficult because of the wide differences in epidemiology and immunology among the major diarrhoea-causing agents. This simplified model provides some theoretical basis for the explanation of a number of observed features of childhood diarrhoea. We hope that it may stimulate others to conduct studies to define more precisely the complex reality. The implications of Fig. 2 for diarrhoea control by reducing pathogen ingestion are as follows. If pathogen ingestion is reduced within the range F-E, the incidence rates of mild or severe diarrhoea may not change. In the range E-D, severe diarrhoea rates may fall, but mild diarrhoea rates may not. Because severe cases usually represent a small proportion of all cases, surveillance of all cases may fail to detect a fall in incidence rate in this range. For instance, if a water supply and excreta disposal project reduced the dose of ingested pathogens from E to D, Fig. 2 suggests that the incidence rate of severe diarrhoea might fall by about 44/o but the incidence rate of all diarrhoea by only about 12%. Many diarrhoeal disease studies are unable to detect a 12% fall in total incidence rate or to show it to be statistically significant. In the range D-E an impact is more likely to be documented if data on the incidence rate of severe diarrhoea (however ' The highest ratios of severe diarrhoea to all diarrhoea have been recorded in some epidemics, which may be associated with excep- tionally high average doses of pathogens ingested by an exposed population. defined) are collected. Measures of diarrhoea or total mortality are also more likely to detect an impact in this range (see below). In the range D-C in Fig. 2, both mild and severe diarrhoea incidence rates are falling, and a change may be detected by surveillance of all cases. Severity, child growth, or mortality parameters are also likely to change in this range. In the range C-B, only the incidence rate of mild cases is declining but, since most cases are mild, surveillance of all cases may detect an impact. In the range B-A, reductions in pathogen ingestion have no effect on diarrhoea of any type. This discussion of the implications of the model presented in Fig. 2 may be restated in two other ways. First, since it is. severe episodes that lead in some instances to death, the mild diarrhoea incidence rate in Fig. 2 may be replaced by the total diarrhoea incidence rate and the severe diarrhoea incidence rate by the diarrhoea mortality rate. Diarrhoea mortality rates may therefore be a more responsive indicator in the range D-E or ranges overlapping with the range D-E than diarrhoea morbidity rates. Diarrhoea mortality rates will not, however, be a good measure of impact in areas where oral rehydration therapy is widely available and averts most deaths from dehydration. Second, since there are putative differences in ID5o values, not only between degrees of severity of diarrhoea caused by a single pathogen, but also among different pathogens, the mild diarrhoea incidence rate may be replaced by the incidence rate of etiologies having low ID5o values, and the severe diarrhoea incidence rate by the incidence rate of etiologies having high IDso values.d This model is consistent with known facts, in that developed countries, which may lie in the range A-C, have a small proportion of cholera and enterotoxi- genic E. coli diarrhoea (high ID5o), a high proportion of rotavirus diarrhoea (low IDso), and an intermediate proportion of shigellosis (intermediate ID50).e It must be emphasized that the model presented in Fig. 2 is hypothetical and grossly simplified. It is, however, consistent with several established facts and, as discussed below, it is helpful in explaining some of the variation in the recorded impacts of water supply and excreta disposal projects on diarrhoeal diseases. A somewhat similar model has been previously published (73). d It is not implied here that pathogens having relatively low ID50 values cause relatively mild diarrhoea and vice versa. This is clearly untrue in the cases of rotavirus and Shigella, both of which have relatively low ID50 values but cause relatively severe diarrhoea. ' This analysis probably only applies to the anthroponotic agents mentioned here. For the zoonotic diarrhoea agents, such as Salmonella and Campylobacter, most transmission in developed countries is from infected animals to man via contaminated food products, and so levels of pathogen ingestion depend more on farming methods, food handling practices, and diet than on domestic water supply and human excreta disposal facilities. IMPROVING WATER SUPPLIES AND EXCRETA DISPOSAL FOR CONTROL OF DIARRHOEAL DISEASES 761 Hypothesis 3. Water supply or excreta disposal improvements can reduce diarrhoea morbidity or mortality rates among young children. Numerous attempts have been made to measure the impact on health of improved water supply or sanitation. We selected for review those 67 studies from 28 countriesf that measured health impact in f Studies were identified from previous reviews, supplemental enquiries to workers in the field, computer searches in five languages, and from unpublished papers presented at the Inter- national Seminar on Measuring the Health Impact of Water and Sanitation Programmes, Cox's Bazaar, Bangladesh, 21-25 November 1983 (sponsored by the International Centre for Diarrhoeal Diseases Research, Bangladesh, and the Ross Institute, London). terms of diarrhoea morbidity, Shigella infection or disease, cholera, Entamoeba histolytica infection, Giardia lamblia infection, nutritional anthro- pometry, diarrhoea mortality, or total mortality. These studies are grouped in Table 1 according to the health impact indicator measured and ordered alpha- betically by country within each group. The data abstracted from the studies listed in Table 1 are summarized in Tables 2-5. All the studies in Table 1 display methodological deficiencies (13, 28) althoug'i some studies were better than others. The total number of studies is large (67), but only a few are reported in sufficient detail to allow an objective assessment of their methodological and analytical Table 1. Studies on the impact of water supply or excreta disposal on diarrhoea morbidity and mortality, enteric infections, total mortality, and nutritional status reviewed in this paper Indicator Country Reference Diarrhoea morbidity Bangladesh 22, 54, 74,a Chile 24 Colombia 51, 88 Costa Rica 62 Egypt 82 Ethiopia 40 Gambia See belowb Guatemala 16, 72 Haiti 79 India 53, 66, 67, 81 Iran (Islamic Rep. of) 82 Kenya 86,c Lesotho 37 Mozambique See belowd Sri Lanka 82 Saint Lucia 44,8 Sudan 6, 82 United Kingdom 17 USA 8, 15, 55, 64, 69, 71, 84 Venezuela 82, 87 Zambia 4 Cholera Bangladesh 22, 46, 49, 50, 54, 76, 77 Philippines 3 Entamoeba histolytica Costa Rica 62 infection Egypt 20 India 59, 66 Kenya See belowc Libyan Arab Jamahiriya 41 USA 15, 29, 57 Table 1: continued on next page 762 S. A. ESREY ET AL. Table 1: continued Indicator Country Reference Giardia lamblia Costa Rica 62infection Egypt 20 India 66 Kenya See below' Libyan Arab Jamahiriya 41 USA 29 Shigella Bangladesh 22, 48, 65,"infection or disease Costa Rica 62 Egypt 82 Guatemala 7 India 66 Iran (Islamic Rep. of) 82 Libyan Arab Jamahiriya 41 Panama 52 Sri Lanka 82 Sudan 82 USA 45, 55, 71, 78, 84 Venezuela 82 Nutritional status Bangladesh See belowa Colombia 2 1 Fiji See below' Nigeria 80 Philippines See belowv Saint Lucia See below" Diarrhoea mortality Brazil 83 India 89 Total mortality Brazil 61 Costa Rica 43 Egypt 85 Guatemala 1 Malaysia 18 Sri Lanka 60, 63 Sudan 6 a RAHAMAN, M. M. The Teknaf Health Impact Study: methods and results. Paper presented at the International Workshop onMeasuring the Health Impacts of Water Supply and Sanitation Programmes, Cox's Bazaar, Bangladesh, 21-25 November 1983.b PICKERING, H. The role of anthropologists in studying diarrhoea epidemiology: a case study from The Gambia. Paper presented atthe International Workshop on Measuring the Health Impacts of Water and Sanitation Programmes, Cox's Bazaar, Bangladesh, 21 -25November 1983. c FENWICK, K. W. H. The short-term effects of a pilot environmental health project in rural Africa: the Zaina scheme re-assessed after four years. (undated manuscript). d CAIRNCROSS, S. & CLIFF, J. Water and health in Mueda, Mozambique. Paper presented at the International Workshop onMeasuring the Health Impacts of Water and Sanitation Programmes, Cox's Bazaar, Bangladesh, 21-25 November 1983. ' YEE, V. S. Household level correlates of child nutritional status in Fiji. MPS thesis. Division of Nutritional Sciences, CornellUniversity, Ithaca, New York, 1984. f MAGNANI, R. J. & TOURKIN, S. C. Impact of improved urban water supplies in the Philippines: methods and results. Paperpresented at the International Workshop on Measuring the Health Impacts of Water and Sanitation Programmes, Cox's Bazaar,Bangladesh, 21-25 November 1983. X HENRY, F. J. Health impact of water and sanitation interventions in St. Lucia. Paper presented at the International Workshop onMeasuring the Health Impacts of Water Supply and Sanitation Programmes, Cox's Bazaar, Bangladesh, 21-25 November 1983. IMPROVING WATER SUPPLIES AND EXCRETA DISPOSAL FOR CONTROL OF DIARRHOEAL DISEASES 763 strength. First, therefore, we analysed the pooled data from all the studies to try to draw a consensus from the many different attempts that have been made in many countries to measure the health impacts of water supply and excreta disposal investments. Second, we examined the results of a few selected studies of superior quality in more detail to compare their findings with those from all 67 studies. The studies listed in Table 1 report impacts on diarrhoea incidence rates and prevalence rates, which are different measures of morbidity due to diarrhoea. If a water supply or excreta disposal project did not affect the mean duration of diarrhoea episodes, the percentage reductions in incidence rates and prevalence rates would be equal. If, on the other hand, the intervention reduced both incidence rates and duration, then the percentage reduction in prevalence rate would be greater than that in incidence rate. In Tables 2-4 reductions in incidence and prevalence rates are combined under the heading of diarrhoea morbidity rate reduction. Impact on diarrhoea morbidity. The median reduction in diarrhoea morbidity rate is 22% (Table 2). The magnitude of this reduction may vary depending on a number of factors: age of study population, type of service compared, general living conditions of the area studied, and etiology of diarrhoea. Each of these factors is examined below. The impact of water supply and excreta disposal improvements on diarrhoea is probably age-specific. Table 2. Percentage reductions in diarrhoeal morbidity rates attributed to water supply or excreta disposal improvements Percentage reduction Type of Number of intervention resultsa Median Range All interventions 53 22 0-100 Improvements in 9 16 0-90 water quality Improvements in 17 25 0-100 water availability, Improvements in 8 37 0-82 water quality and availability Improvements in 10 22 0-48 excreta disposal a There are 53 results in total but only 44 attributed to specific interventions. The remaining 9 results are for other interventions or combinations of interventions having less than 3 results, and include interventions in fly control and health education together with water supply or excreta disposal. Different age groups have different pre-intervention diarrhoea rates, different risk factors, and different tendencies to utilize new water supply or excreta disposal facilities. However, no consistent difference by age in the magnitude of the impact was apparent (data not shown). This suggests that all ages will benefit from improvements, despite the fact that young children do not use latrines. The type of water supply or excreta disposal service provided is likely to influence the size of the impact. Improvements in water quality had less of an impact on diarrhoea rates than did improvements in water availability or excreta disposal (Table 2). Impacts from water quality plus availability were greater than from either of these improvements separately or from improvements in excreta disposal. The magnitudes of the reductions due to individual service components shown in Table 2 are probably overestimates because situations labelled, for instance, as water quality improvement may well have contained some element of water availability improvement. Data on the impact of water quality improvement, with both water availability and excreta disposal controlled, are not available. This factor may also lead to an underestimate of the magnitude of the differences among the impacts of the different types of service improvement analysed in Table 2. The magnitude of the impact is likely to be influenced not only by the type of service installed but also by the level of service both before and after the intervention and the living conditions of the study area. All studies of diarrhoea morbidity (Table 1) were therefore divided according to the magnitude of the difference between pre-intervention and post- intervention levels of service (big difference or small difference)9 and according to the adult literacy rate of the country in which the study was conducted (<40%7o, 40-75%0, > 750/o). Adult literacy is used here as a proxy for pre-intervention levels of hygiene and faecal contamination; in other words, to define the pre-intervention point on the horizontal axis of Fig. 2. Current adult literacy figures are used, assuming that the relative ranking of countries, according to adult literacy, has not changed over the past 30 years. The impacts of studies, categorized by adult literacy rate and magnitude of service improvement, are shown in Table 3. Impacts attributed to large service-level improve- ments are consistently higher than impacts attributed I A study was considered to have investigated a large service improvement if one or more of the following comparisons was made: in-house water vs. public water source, piped water vs. unpiped water, water near and plentiful vs. water scarce or far, any toilet vs. no toilet, flush toilet vs. other toilet, or studies in which more than one service component was improved (water quality and water availability, water quality and excreta disposal, water availability and excreta disposal, water quality and water availability and excreta disposal). 764 S. A. ESREY ET AL. Table 3. Percentage reductions in diarrhoea morbidity rates attributed to water supply or excreta disposal improvements by adult literacy rate of the country and magnitude of service improvement Small service Large service Adult improvementsb improvementsb literacy ratea No. of Median No. of Median (%) results (%) results (%) <40 11 18 7 46 40-75 4 20 8 39 > 75 10 16 13 32 e Data on adult literacy, by country, from World development report, 1983 (Washington, World Bank). b See footnote g, page 762. to small service-level improvements (Table 3). If a large service-level improvement is made, the percentage reduction in diarrhoea morbidity rates achieved is inversely related to the pre-intervention level of hygiene (Table 3). The greatest impact is achieved when the pre-intervention hygiene level is worst. For small improvements in service level, impacts appear less dependent upon the pre- intervention hygiene level. These conclusions are consistent with the hypothetical model depicted in Fig. 2 and suggest that the impact of water and sanitation improvements depends in part on the presence and interaction of other risk factors. Impact on specific infections. When impact on total diarrhoea morbidity is broken down by etiology, it is likely, as discussed above, that different specific dOiarrhoeas will be reduced by different amounts. Table 4 presents data on impacts on cholera, Shigella infection or disease, and infection by Ent. histolytica and G. lamblia. Since the distinction between the severe and mild diarrhoea bands in Fig. 2 is merely one of infectious dose (ID), in ranges including D-E, any reduction in pathogen ingestion will produce a greater percentage reduction in the incidence rate of the high ID etiologies than the low ID etiologies. Thus the impact of a water supply and excreta disposal improvement (in ranges including D-E) on specific etiologies may be in the following descending order of magnitude: cholera, enterotoxigenic E. coli, Shigella, the protozoa, rotavirus. The relative impacts on Shigella and the protozoa are supported by the data in Table 4. The anomalous cholera data are discussed elsewhere (31). Data on the impact of water supply and excreta disposal projects on enterotoxigenic E. coli and rotavirus incidences are not yet available, but it is anticipated that the impact on enterotoxigenic E. coli will be considerable and on rotavirus negligible. The latter prediction is indirectly supported by data show- ing that the incidence rate of rotavirus diarrhoea among children under 2 years of age is 0.3-0.4 episodes per child per year in both Bangladesh (11) and Winnipeg, Canada (42). Impact on nutritional anthropometry. If water supply and excreta disposal improvements reduce diarrhoea incidence rates or duration among young children, then nutritional anthropometric indicators should also improve because of the inverse relation- ship between time spent with diarrhoea and child growth (58, 68). Six studies that investigated the relationship between water supply or excreta disposal improvements and nutritional status are summarized in Table 5. All six studies reported an association between improved water supply or excreta disposal and improved nutritional status. In two studies, in Fiji and the Philippines, attempts to control for extraneous risk factors reduced the differences between the control and intervention groups, but some of these differences were nonetheless found to be statistically significant. Impact on mortality. Only two studies were located that reported the impact of water supply or excreta disposal improvements on diarrhoea mortality rates (Table 1); a 41 o median reduction in diarrhoea mortality rate was calculated from them. Both studies were concerned with the impact of improved water supplies in urban areas, and in neither was the study method well described. A further eight studies reported impacts of water supply or excreta disposal improvements on mortality from all causes (Table 1), and they indicated a 21% (range, 0-81O7o) median reduction in mortality rate. Table 4. Percentage reductions in morbidity or infection rates of cholera, Shigella, Entamoeba histolytica, and Giardia lamblia attributed to water supply or excreta disposal improvements Percentage reduction Disease or No. of Median Range infection results (%) (%) Cholera 11 41 0-91 Shigella 27 48 0-81 Entamoeba histolytica 17 2 0-80 Giardia lamblia 10 0 0-20 IMPROVING WATER SUPPLIES AND EXCRETA DISPOSAL FOR CONTROL OF DIARRHOEAL DISEASES 765 Table 5. Improvements in nutritional status attributed to various types of water supply or excreta disposal improve- ment Value of indicator Country Nutritional Age Type of Control Target Referenceindicator' (months) intervention group group Bangladesh Percentage with H/A > 90% of standard Percentage with W/A > 75% of standard Colombia Percentage with W/A > 90% of standard Percentage with H/A > 95% of standard Fiji Mean percentage of: standard W/A urban rural standard H/A urban rural Nigeria Percentage with: W/A > 75% of standard H/A > 90% of standard W/H > 80% of standard Philippines Percentage with W/A > 75% of standard pre-intervention post-intervention Saint Lucia Percentage with W/A > 90% of standard 0-11 Q+A+E 12-23 Q+A+E 24-35 Q+A+E 0-11 Q+A+E 12-23 Q+A+E 24-35 Q+A+E 6-30 6-30 6-30 6-30 0-59 0-59 0-59 0-59 6-59 6-59 6-59 E A E A E E E E A A A 6-54 6-54 Q+A 1-3 4-6 7-9 10-12 13-15 16-18 19-21 22-24 A (A+E) 75 76 See belowd 50 51 45 48 59 63 44 43 47 50 26 47 21 22 51 26 48 20 53 See belowe 102 100 95 102 100 100 99 103 80 50 69 80 69 63 90 See belowf 74 75 71 80 93 92 (86)C See belowg 72 90 (88) 51 78 (76) 44 76 (73) 50 76 (58) 51 74 (57) 53 75 (66) 54 79 (71) a W/A = weight for age; W/H = weight for height; H/A = height for age. b Q = water quality improvement, A = water availability improvement, E = excreta disposal improvement. ' Figures not in parentheses refer to the communities receiving water availability improvements (A). Figures in parentheses refer to communities receiving water availability improvements plus excreta disposal facilities (A + E). d See footnote a to Table 1. ' See footnote e to Table 1. f See footnote f to Table 1. 8 See footnote g to Table 1. 766 S. A. ESREY ET AL. Fig. 2 predicts a larger impact on diarrhoea mortality than morbidity over a wide range of conditions. The impact on total mortality will depend on the proportion of all mortality that is due to diarrhoea and the degree to which water supply and excreta disposal improvements affect the causes of death other than diarrhoea. Since water supply and excreta disposal improvements will have little impact on some major causes of death (for instance, respiratory infection, measles, malaria, and neonatal tetanus), it is to be expected that the impact on diarrhoea mortality is considerably greater than the impact on all mortality. Results from selected studies. For the analyses so far, we have used pooled data from all studies listed in Table 1 to give an overview of all documented experiences on the impacts of water supply and excreta disposal improvements on diarrhoea. It is instructive to compare these findings with the results of a few of the better studies. Criteria for judging the quality of each study have been developed and are reported elsewhere (28). The first finding from this selective analysis was that all studies that reported a negative impact were flawed in one or more major respects. In other words, the better studies consistently reported positive impacts. The best studies were on total mortality (18, 43, 60), and the median impact on total mortality rates reported from these studies was a reduction of 30%o. Analysis for statistical interactions revealed a range of reductions in mortality rates of 8-64%, depending on the type of intervention and on the presence of other risk factors, such as poor feeding practices and low literacy rates. For example, in one study (18) excreta disposal improvements were reported to have a larger impact on infant mortality rates than water supply, but the magnitudes of these impacts were greatly affected by whether the infants were breast- fed. The impact of the environmental interventions was greater for non-breast-fed infants than for breast- fed infants. Thus, it is likely that non-breast-fed infants were further to the right along the horizontal axis in Fig. 2 than were breast-fed infants. Another study reported that excreta disposal improvements had a greater impact on mortality in families with literate mothers than in families with illiterate mothers (60). This may reflect an increased ability of literate mothers to make correct use of the new excreta disposal facilities. Two studies on nutritional status also examined statistical interactions. In one,h excreta disposal was reported to have more impact in rural than in urban h YEE, V. S. Household level correlates ofchild nutritional status in Fiji. MPS thesis. Division of Nutritional Sciences, Cornell University, Ithaca, New York, 1984. areas. In the other,' water quality improvements had an impact only among higher income households. Studies on diarrhoea morbidity were not as well controlled as the mortality studies referred to above. A median reduction in diarrhoea morbidity rates of 27% (range, 0-68%) was found in the studies judged to be most satisfactory (40, 51, 55, 71). ji k, I This brief review of selected studies of superior design leads to two conclusions. First, the median. reductions in diarrhoea morbidity rates (27%) and total mortality rates (30%) are a little higher than the values found by analysing all studies. Second, the magnitude of the impact depends greatly on the presence of other risk factors. More knowledge of these interactions would enable the appropriate type of intervention to be targeted to families that are likely to benefit the most. FEASIBILITY Nearly all developing countries are currently engaged in substantial programmes to improve water supplies in both rural and urban areas. The urban programmes date back, in many cases, to the 1920s or earlier, while many of the rural programmes were initiated in the 1960s. This considerable experience in water supply programmes throughout the world has been copiously documented (e.g., 23) and is con- tinuously monitored by WHO.m Improved water supplies can be provided to almost all people in all developing countries, and the technologies for achieving this are, for the most part, well established. Several problems remain, however, such as poor operation and maintenance, inappropriate choice of technology, inadequate revenue collection, failure to sustain community participation, and high rates of water leakage and wastage. All countries have experience in excreta disposal MAGNANI, R. J. & TOURKIN, S. C. Impact ofimproved urban water supplies in the Philippines: methods and results. Paper presented at the International Workshop on Measuring the Health Impacts of Water and Sanitation Programmes, Cox's Bazaar, Bangladesh, 21-25th November 1983. j CAIRNCROSS, S. & CLIFF, J. Water and health in Mueda, Mozambique. Paper presented at the International Workshop on Measuring the Health Impacts of Water and Sanitation Programmes, Cox's Bazaar, Bangladesh, 21-25 November 1983. k PICKERING, H. The role of anthropologists in studying diarrhoea epidemiology: a case study from the Gambia. Paper presented at the International Workshop on Measuring the Health Impacts of Water and Sanitation Programmes, Cox's Bazaar, Bangladesh, 21-25 November 1983. / RAHAMAN, M. M. The TeknafHealth Impact Study: methods and results. Paper presented at the International Workshop on Measuring the Health Impacts of Water Supply and Sanitation Programmes, Cox's Bazaar, Bangladesh, 21-25 November 1983. "' See, for example, World Health Statistics Report, Vol. 26, No. 11, 1973; World Health Statistics Report, Vol. 29, No. 10, 1976; and The International Drinking Water Supply and Sanitation Decade. Review of national baseline data (as at 31 December 1980), Geneva, World Health Organisation, 1984 (WHO Offset Publication No.85). IMPROVING WATER SUPPLIES AND EXCRETA DISPOSAL FOR CONTROL OF DIARRHOEAL DISEASES 767 programmes in urban areas, in some cases dating back thousands of years. Rural excreta disposal programmes are typically a new phenomenon, and some countries still lack concerted efforts in this sector. Problems commonly encountered in excreta disposal programmes include the inappropriate choice of technology, poor operation and main- tenance, inadequate revenue collection, and the lack of perception in many rural communities of the importance of improved excreta disposal practices. Research into the technical, economic, and social aspects of excreta disposal in developing countries (e.g., see 47) over the past decade has led to some promising new approaches. COSTS Despite the extensive experience with water supply and excreta disposal projects throughout the world, the cost data on these projects are often of poor quality and not strictly comparable. Data on operation and maintenance costs, on institutional overhead costs, and on the costs of community mobilization and education, are especially deficient. Table 6 presents cost data from 87 developing countries. Costs vary widely depending upon the design criteria adopted in different countries and upon the costs of labour and materials. The costs of operation and maintenance (recurrent costs) must be added to the construction costs, and data on these costs are not readily available. One study of excreta disposal in 12 countries estimated that operation and maintenance accounted for between 4%o and 520/o of the total project costs per year, depending on the technology under consideration (47). Several widely used technologies (for instance, sewerage and pour- flush latrines) had operation and maintenance costs that comprised approximately 30% of the total annual project costs. For rural water supplies, data assembled by a UNDP/World Bank project' suggest that the same figure, 300/, is a reasonable estimate of the proportion of the total annual costs taken up by operation and maintenance. The 307o figure is adopted in Table 6 for both water supplies and excreta disposal.' Reliable data on the costs of software support (such as the promotion of community par- UNDP project INT/81/026. o The computation of the percentage of total annual costs due to operation and maintenance requires the adoption of a discount rate (or opportunity cost of capital). Choosing the discount rate is partly a matter of judgement, and different economists may advocate different rates for the analysis of the same project. The choice of a high discount rate (say, 20%) will reduce the apparent importance of recurrent costs within total project costs. If a low discount rate (say, 5%) is chosen, perhaps to reflect the scarcity of recurrent funds (5), the proportion of total costs that is attributed to operation and maintenance will be greatly increased. Table 6. Costs for urban and rural water supply and excreta disposal projects Annual Annual construction total Construction cost cost per cost per per capita Lifetime capita capita Type of service (1982, US$)° (years)b (1982, US$) (1982, US$)d Water supply Urban House connection 116 20 14 20 Publictap 66 20 8 11 Rural' 60 20 7 10 Sanitation Urban Sewerage 174 50 18 26 Other 66 20 8 11 Rural 19 10 3 4 a Median values of the costs from 87 developing countries reported to WHO. For further information, see The International Drinking Water Supply and Sanitation Decade. Review ofnational baseline data (as at 31 December 1980), Geneva, World Health Organization, 1984 (WHO Offset Publication No. 85). b Commonly assumed values. c Assuming an opportunity cost of capital (discount rate) of 10%. d Assuming that construction costs are 70% of the total annual costs (see text). ' A variety of technologies are included here, but predominantly public taps and handpumps. 768 S. A. ESREY ET AL. ticipation or hygiene education) and of apportioned institutional overheads have not been located, and so these costs, which are not trivial, have been omitted from the calculations. Total annual costs per capita are derived in Table 6, assuming that recurrent costs comprise 30% of the total annual costs, that project lifetimes are between 10 and 50 years (depending upon the technology), and that the appropriate discount rate is 1007o. The total annual costs per capita in Table 6 may be aggregated to derive the costs of complete water supply and excreta disposal interventions. For instance, a rural water supply and excreta disposal project might cost US$ 14 per capita annually ($10 + $4), whereas a combination of in-house water and sewerage in an urban area might have an annual cost of US$ 46 per capita ($20 + $26). A goal of this series of reviews (38) is to derive cost- effectiveness estimates for each intervention. Special difficulties are inherent in applying the cost- effectiveness analysis to interventions having multiple benefits, and water supply and excreta disposal interventions present these difficulties in an extreme form (9, 14). In addition to their impact on diarrhoea rates among young children, these interventions may avert diarrhoea in other age groups, reduce the incidence of other infectious diseases, and have a variety of benefits unrelated to health. In view of this, a treatment of the cost-effectiveness of water supply and excreta disposal in relation to other diarrhoea control measures will be left to a later publication. CONCLUSIONS The results in Tables 2-4 show that substantial reductions in diarrhoea morbidity and mortality rates can be expected from investments in water supply and excreta disposal. Table 2 suggests that investments that improve both water quality and availability are especially effective. There are no adequate data on the impact of improvements in water quality plus availability together with excreta disposal. Likewise, the available data do not permit an assessment of the advantages of adding a hygiene education component to a project, but analysis of hygiene education alone suggests that it may further enhance the impact (34). Taking all this evidence together, and in view of the impact of large service-level improvements shown in Table 3, it is possible that well-designed projects combining water supply, excreta disposal and hygiene education may achieve diarrhoea morbidity rate reductions of 35-50%. It is to be expected that, in any given project, the impact on diarrhoea mortality rates will be larger than that on diarrhoea morbidity rates, except in areas where other interventions, such as oral rehydration programmes, have substantially reduced the risk of death from diarrhoea. This review highlights some of the deficiencies in our knowledge of the impacts of water supply and excreta disposal on diarrhoea. More studies of these impacts are required, and it is expected that current advances in methodologyP will enable such studies to be undertaken retrospectively and at reasonable cost. The model discussed under hypothesis 2 suggests that there may be advantages in measuring the impact on severe diarrhoea rather than all diarrhoea. Where etiology-specific studies are being conducted, they are more likely to record impacts on diarrhoea due to agents having high infectious doses than on diarrhoea due to agents having low infectious doses. The most pressing research need is to document the impact on diarrhoea of projects that combine improvements in water quality, water availability and excreta disposal with hygiene education that are functioning satis- factorily and are being utilized by the intended bene- ficiaries.q P BRISCOE, J. ET AL. Measuring the impacts of water supply and sanitation projects on diarrhoea: prospects for case-control methods (in preparation). " Minimum evaluation procedure (MEP) for water supply and sanitation projects. Unpublished document WHO/ETS/83.1, 1983. ACKNOWLEDGEMENTS We are grateful for the constructive criticisms of earlier drafts of this paper provided by R. C. Ballance, D. Blum, J. Briscoe, A. M. Cairncross, I. de Zoysa, B. H. Dieterich, F. L. Golladay, M. B. Grieveson, R. C. Hogan, J. S. Koopman, L. Laugeri, D. D. Mara, M. H. Merson, R. N. Middleton, M. Phillips, M. M. Rahaman, G. Schultzberg, S. Unakul, and A. M. Wright. Secretarial, bibliographic and editorial assistance were most ably provided by Caprice Mahalla, Susanne O'Driscoll, and Dianne Fishman. IMPROVING WATER SUPPLIES AND EXCRETA DISPOSAL FOR CONTROL OF DIARRHOEAL DISEASES 769 R-SUMt LA LUTTE CONTRE LES MALADIES DIARRHEIQUES DU JEUNE ENFANT: INTERVENTIONS VISANT A AMELIORER L'APPROVISIONNEMENT EN EAU ET L'ELIMINATION DES EXCRETA Cet article est le neuvieme d'une serie d'analyses consacrees aux mesures possibles pour lutter contre les diarrhees. Dans les pays en developpement, l'impact des projets d'approvisionnement en eau et d'evacuation des excreta sur les maladies diarrheiques a e au centre de tres nombreuses discussions et recherches. Quelques observa- tions donnent A penser que des ameliorations portant sur la qualite de l'eau, l'approvisionnement en eau, l'hygiene individuelle et l'evacuation des excreta, reduiraient l'ingestion des agents pathogenes A l'origine de diarrhees. On expose ici un modele theorique qui etablit une relation entre la quantite ingeree d'agents pathogenes responsables de diarrhees et la frequence de ces affections dans la communaute. Ce modele montre que, dans des communautes pauvres, mal approvisionnees en eau et ou l'evacuation des excreta se fait de faqon insalubre, la diminution de la quantite d'agents enteropathogenes ingeree exerce, A valeur egale, un impact plus grand sur les taux de mortalite que sur ceux de morbite. Elle ameloire davantage les diarrhees graves que les diarrhees benignes et plutOt celles dont les agents etiolo- giques agissent A dose elevee. Le recensement de 67 etudes effectuees dans 28 pays permet d'analyser l'impact de l'approvisionnement en eau et de l'evacuation des excreta sur les maladies diarrheiques, les infections apparentees, l'etat nutritionnel et la mortalite. Toutes ces etudes montrent une diminution mediane de 22%7 des taux de morbidite associes aux maladies diarrheiques, la diminution atteignant 27% dans quelques etudes mieux concues; pour le taux de mortalite global, la diminution re'diane a e de 21 %, atteignant 30% dans les quelques etudes mieux concues. L'amelioration de la qualite de l'eau importante moins que celle de I'approvisionnement ou de 1'evacuation des excreta. Mieux vaut ameliorer la qualite de 1'eau et I'approvisionnement qu'un seul de ces elements ou que l'elimination des excreta. Les projets d'approvisionne- ment en eau et d'evacuation des excreta ont un impact plus important sur la shigellose que sur les infestations a Entamoeba histolytica ou a Giardia lamblia, mais on ignore quelles peuvent en etre les repercussions sur les diarrhees causees par Escherichia coli enterotoxigene ou les rotavirus. Les six etudes portant sur les repercussions de l'approvision- nement en eau ou de l'evacuation des excreta sur l'etat nutritionnel ont fait etat d'une amelioration. L'article presente ensuite une analyse des donnees sur les coQts de construction pour les projets d'approvisionnement en eau et d'assainissement dans 87 pays en developpement. Si l'on ajoute les coQts d'exploitation et d'entretien, sans tenir compte des couts lies a la mobilisation et a l'education de la communaute ni des frais generaux institutionnels, on arrive a un total median de 14-46 dollars E.-U. (prix de 1982) par tete, selon l'importance du service. 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