The role of the World Bank in international health: renewed commitment and partnership

During the course of the past ten years, the World Bank has become the single largest external financier of health activities in low and middle income countries and an important voice in national and international debates on health policy. This article highlights the Bank's new strategic direction in the health sector aimed at: improving health, nutrition, and population outcomes of the poor; enhancing the performance of health care systems; and securing sustainable health care financing. Millions of preventable deaths and treatable illnesses, together with health systems that are inefficient, inequitable and ineffective, have motivated expanded Bank support for the health sector in many of its client countries. The new policy directions and system-wide reforms observed in these countries are the result of both demand and supply factors. It is part of a general shift in the Bank's approach to development assistance, which sees systemic reform as a way to improve the impact and sustainability of investments in health. On the demand side, the Bank is trying to adapt to ongoing political, technological, economic, demographic, epidemiological and social pressures. On the supply side, the Bank's growing international experience and substantial financial resources are used to complement the development assistance provided by other organizations and the global effort to improve health and health systems in low and middle income countries.

Adult health: a legitimate concern for developing countries

Adults, defined here as people between 15 and 59 years of age, in developing countries have a high risk of premature death and suffer from frequent morbidity and high rates of chronic impairment. Their ill health imposes a major burden on health services and large negative consequences on families, communities, and societies. This paper describes the level and impact of adult mortality and morbidity, and highlights some of its characteristics and causes, which in some cases contradict commonly held beliefs. It concludes that "adult health" is a legitimate public health concern for developing countries that is not being addressed. An agenda for remedial research and action is proposed.

Excreta disposal behaviour and latrine ownership in relation to the risk of childhood diarrhoea in Sri Lanka

A case-control study of environmental and behavioural risk factors for childhood diarrhoea was conducted in Kurunegala district, Sri Lanka. From five hospitals, 2458 children aged less than 5 years and suffering from diarrhoea were recruited as clinic cases, and a further 4140 reporting with complaints other than diarrhoea were recruited as clinic controls. Community-based cross-sectional surveys were also conducted in three of the five areas served by these hospitals, and from these a further 1659 children were recruited as community controls. Children from households where excreta were reported to be disposed of in a latrine were less likely to have diarrhoea than children whose families improperly disposed of excreta. The results obtained from comparisons of cases with clinic controls (adjusted odds ratio [OR] 1.42, 95% confidence interval [CI] : 1.01-1.98), and of cases with community controls (OR 1.35, 95% CI : 0.85-2.13) were in agreement, suggesting that no important selection bias operated on this association. If the observed proportion (91%) of improper excreta disposal among the population could be reduced to 50%, 12% of childhood diarrhoea episodes would be prevented. Although latrine ownership may be a necessary condition for safe excreta disposal behaviour, diarrhoeal morbidity may only be reduced in Sri Lanka if behavioural changes take place concomitant with the construction of sanitation facilities.

A study of the association between improved sanitation facilities and children's height in Lesotho

The impact of improved sanitation on the anthropometric status of children under 5 years in Lesotho was investigated using children recruited into a case-control study of diarrhoea morbidity. The children's height-for-age Z-scores were used as an indicator of chronic undernutrition. Classifying children as 'stunted' or 'adequately nourished' revealed some evidence of an association between latrine ownership and attained height. After allowing for confounding variables, the odds of stunting were 18 per cent lower among children in households with latrines (95 per cent confidence interval, 36 per cent lower to 3 per cent higher). More powerful analyses, using height-for-age as a continuous outcome variable, revealed that the mean height-for-age Z-score of children from households with a latrine was 0.27 standard deviations higher than that of children from households without a latrine (95 per cent c.i. = 0.12 to 0.42). These results suggest that the anthropometric status of children may be as responsive to improvements in sanitation facilities as diarrhoea morbidity in some settings.

Reduction in diarrhoeal diseases in children in rural Bangladesh by environmental and behavioural modifications

The impact of a water, sanitation and hygiene education intervention project on diarrhoeal morbidity in children under 5 years old was evaluated in a rural area of Bangladesh. Data were collected throughout 1984-1987, covering both pre- and post-intervention periods, from an intervention and a control area. The 2 areas were similar with respect to most socio-economic characteristics and baseline levels of diarrhoeal morbidity. The project showed a striking impact on the incidence of all cases of diarrhoea, including dysentery and persistent diarrhoea. By the end of the study period, children in the intervention area were experiencing 25% fewer episodes of diarrhoea than those in the control area. This impact was evident throughout the year, but particularly in the monsoon season, and in all age groups except those less than 6 months old. Within the intervention area, children from households living closer to handpumps or where better sanitation habits were practised experienced lower rates of diarrhoea. These results suggest that an integrated approach to environmental interventions can have a significant impact on diarrhoeal morbidity.

The Imo State (Nigeria) Drinking Water Supply and Sanitation Project, 1. Description of the project, evaluation methods, and impact on intervening variables

A health impact evaluation was conducted in conjunction with the Imo State Drinking Water Supply and Sanitation Project in Nigeria. The project consisted of a package of water supply, sanitation, and health and hygiene education given by village-based workers. The evaluation was a quasi-experimental study covering pre-, peri- and post-intervention periods. Data were collected from 3 intervention and 2 control villages. Baseline surveys indicated that the intervention and control areas were similar with respect to most socio-demographic variables. Use of the improved water supply was high, although this was influenced by borehole-to-population ratios and household-to-borehole distances. Water collection time was consequently greatly reduced. Data from a small sample of households showed that borehole water became heavily contaminated during collection and storage, and that there was no significant change in consumption of water per person. Adults in 46% of household units in the intervention area were using ventilated improved pit latrines by the end of the study period. Use by young children (2-5 years old), however, was low. Limitations in the success of the health education component of the project were found. Although changes were found in knowledge, attitudes and practices related to water and sanitation, and in management of childhood diarrhoea, this occurred in both the intervention and control areas.

Health impact evaluation of improved water supplies and hygiene practices in Sri Lanka: background and methodology

Between January 1987 and March 1988 a Health Impact Evaluation (HIE) of the Rural Water Supply and Sanitation Project (RWSSP) was conducted in Kurunegala District. Four related activities were undertaken: 6598 children were recruited into a case-control study of diarrhoea morbidity conducted in five hospitals; an additional 1649 children from the catchment areas of three of the five hospitals were recruited as a community comparison group; environmental microbiology was performed on water samples collected during 3092 visits to the homes of children recruited into the study; diagnostic stool microbiology was performed for 371 children with diarrhoea and 121 controls. In this paper the seasonality of reported diarrhoea and the socio-demographic characteristics and health-related behaviours of each study group are examined. Cases, clinic controls and the community comparison group were all drawn from the essentially rural settlements typical of the southern part of the dry zone of Sri Lanka. The majority of households in these settlements are Sinhalese buddhist, and the main economic activity is subsitence farming. There was some evidence of differences between the three groups, community recruits tending to come from larger and wealthier households than the children recruited at the hospitals. Issues arising in the design and analysis of this Health Impact Evaluation are discussed. In particular, potential sources of bias are examined and the question of validity investigated.

The Imo State (Nigeria) Drinking Water Supply and Sanitation Project, 2. Impact on dracunculiasis, diarrhoea and nutritional status

Morbidity due to dracunculiasis (guinea worm disease) and diarrhoea in persons of all ages, and nutritional status of young children, were used as health impact indicators in the evaluation of the Imo State Drinking Water Supply and Sanitation Project in south-eastern Nigeria. Data were collected using repeated cross-sectional surveys and longitudinal follow-up. The study area was found to have a low level of endemicity of dracunculiasis. While no impact could be demonstrated on overall period or point prevalence rates in the cross-sectional surveys, a prospective longitudinal survey showed a significant reduction in the percentage of person-fortnights positive for dracunculiasis in areas served by the project, while the control areas showed no such change. In the cross-sectional surveys it was found that, in the project villages, those persons drinking only borehole water had significantly lower period prevalence rates one year later than others. Moreover, those living further from the nearest borehole had higher rates of dracunculiasis. An impact of the project on diarrhoea morbidity was found only in limited sub-groups of the population. A greater association with water availability rather than quality was suggested for rates in young children. The prevalence of wasting (less than 80% weight-for-height) among children aged less than 3 years decreased significantly over time in all 3 intervention villages; there was no such decline in the control villages.

Childhood diarrhoea in Sri Lanka: a case-control study of the impact of improved water sources

Between January 1987 and March 1988 a case-control study of the impact of improved water sources on childhood diarrhoea was conducted in Kurunegala District, Sri Lanka. Two thousand four hundred and fifty eight cases of diarrhoea were recruited at five of the hospitals in the district. Another 4140 children presenting at the same hospitals with complaints other than diarrhoea were recruited as controls. Data from the five hospitals suggest that children in households drawing their drinking water from handpumps suffer 46% fewer episodes of diarrhoea than children in families using unprotected traditional sources (95% c. i. 29-59%), while children in families using protected traditional wells suffer 35% fewer episodes than children in families using unprotected traditional sources (95% c. i. 27-41%). There were, however, substantial differences between the different hospitals. Among children recruited at one of the hospitals, the reduction in diarrhoea rates associated with the use of improved sources was estimated to be 93% compared with an average of 18% for the other four hospitals. In common with other case-control studies conducted in Malawi and the Philippines, little evidence of confounding of the association between diarrhoea and water supply was observed. Our results suggest that, in Sri Lanka, the use of improved water supplies, including protected traditional wells, rather than unprotected traditional sources may lead to a substantial reduction in diarrhoea morbidity among children under five years of age.

A case-control study of the impact of improved sanitation on diarrhoea morbidity in Lesotho

A health impact evaluation of the Rural Sanitation Pilot Project in Mohale's Hoek district, Lesotho, was conducted from October 1987 to September 1988. A clinic-based case-control design was used to investigate the impact of improved sanitation on diarrhoea morbidity in young children. The results indicate that under-5-year-olds from households with a latrine may experience 24% fewer episodes of diarrhoea than such children from households without a latrine (odds ratio = 0.76; 95% confidence interval, 0.58-1.01). The impact of latrines on diarrhoea was greater in those households that used more water, practised better personal hygiene, and where the mothers had a higher level of education or worked outside the home. In common with studies conducted in Malawi, Philippines, and Sri Lanka, little evidence was found that the relationship between latrine ownership and diarrhoea was confounded by socioeconomic status or environmental variables. For a sample of cases and controls, data on exposure status (presence or absence of a latrine) that were collected by interview at the clinics agreed closely with those obtained by observation during a home visit.

Enterotoxigenic Escherichia coli in the domestic environment of a Malaysian village

The membrane-filter assay, GM1-ELISA, and DNA-DNA hybridization assay, were used to detect enterotoxigenic Escherichia coli (ETEC) in samples of water, weaning food, food preparation surface swabs, fingerprints of mothers, and the fingerprints and stools of children under 5 years of age, in 20 households in a Malaysian village. Weaning food and environmental samples were frequently contaminated by faecal coliforms, including ETEC. The membrane-filter assay detected and enumerated faecal coliforms and LT-ETEC in all types of water and weaning food samples. Highest concentrations of faecal coliforms and LT-ETEC were found in weaning food, followed by well-water, stored water and stored drinking water. The GM1-ELISA detected LT-ETEC in weaning food, food preparation surfaces, fingerprints and stool samples. The DNA-DNA hybridization assay detected a larger proportion of STa2-ETEC than the other toxotypes, either singly or in combination. All the assays in combination detected the presence of ETEC in all types of samples on at least one occasion in each household. It was not possible to classify households as consistently more or less contaminated with ETEC. On individual occasions it was possible to show a significant association of the presence of LT-ETEC between the fingerprints of children and their stools, fingerprints of mothers and children, and weaning food and the stools of the child consuming the food.

Persistent diarrhoea in a rural area of Bangladesh: a community-based longitudinal study

As part of a health impact evaluation of a water supply and sanitation project in a rural area of Bangladesh, diarrhoeal morbidity was recorded in children 0-4 years of age using weekly recall in household interviews, during the period March 1984 to December 1987. During the baseline year, 1984, the incidence rate of all diarrhoea episodes (3.8 episodes per child per year), and those defined as persistent, duration greater than 14 days (0.6 episodes per child per year), showed a similar age distribution, peaking in the 12-23 month age group. Sixteen per cent of all episodes were classified as persistent, and this proportion was greatest in the 0-5 month age group (25%). Children suffering at least one episode of persistent diarrhoea in 1984 also experienced a higher incidence of acute diarrhoea (less than = 14 days duration) than those suffering acute diarrhoea only (4.2 versus 3.7 episodes per child per year). Persistent diarrhoea showed a similar seasonal pattern to that of all episodes. Rates of abdominal pain, isolation of Shigella spp and a diagnosis of dysentery were significantly higher in persistent episodes than in acute episodes. Closer follow-up of children during 1986 and 1987, through the recording of all periods of absence of the child from the home, showed that overall diarrhoea incidence rates were little affected when absence was taken into account, but that the incidence of persistent diarrhoea and the proportion of episodes classified as persistent were significantly reduced. The implications of this methodological problem are discussed.

The use of nutritional status as a second outcome measure in case-control studies of environmental risk factors for diarrhoeal diseases

Case-control studies are typically used to study the effect of several factors on the risk/incidence rate of a single disease. This paper describes a particular situation in which it is of interest to study the effect of a factor--improved sanitation facilities--on the risk/incidence rate of two 'diseases'--the incidence rate of diarrhoea and the risk of undernutrition. The conditions under which it is valid to perform an analysis of the association between the risk factor (unimproved sanitation) and a second outcome variable (undernutrition) are examined. If the effect of exposure status (improved/unimproved sanitation facilities) on the propensity to report an episode of diarrhoea is independent of the effect of nutritional status it appears that such an analysis may be valid. There must also be no interaction between the risk factor (unimproved sanitation) and the second outcome (undernutrition) with respect to their effects as risk factors for the first outcome variable (diarrhoea incidence rate).

Tubewell water consumption and its determinants in a rural area of Bangladesh

As part of the evaluation of a water supply, sanitation and hygiene education project in rural Bangladesh, the consumption of water from the improved supplies was estimated from an observational study. Women volunteers observed and recorded all water collection activities of each group of households using a handpump over a 2-day period. Data from questionnaire surveys on household characteristics were related to per capita use of water. The mean household water consumption rate was 43 l per capita per day. Univariate analyses showed that several factors were significantly associated with water consumption, including family size and age structure, occupation, distance from the house to the handpump, the number of people served by a handpump, and possession of luxury items. Multiple regression analysis showed that several factors remained associated with per capita consumption, although their predictive value was low. The method of measuring water consumption, and the policy implications of the findings, are discussed.

Identifying health problems and health research priorities in developing countries

When we were invited to prepare this background paper on the health problems of the developing countries for the Commission on Health Research for Development, our first thought was to compile and organize available data on the causes of morbidity and mortality affecting different age groups in various populations. It soon became clear that this would not be especially useful. There are major gaps in the available data, particularly from the poorer countries and for people above 5 years of age. The data that are available are often of poor or uncertain quality, collected from unrepresentative or undefined subpopulations, and not strictly comparable due to different definitions and data-collection methods. Additionally, in the absence of agreed definitions and analytical frameworks, it is not clear what could or should be done with the data on health problems so amassed. More fundamentally, we have come to doubt whether the current array of epidemiological concepts and tools is sufficient for the task. We therefore decided that, while giving an overview of current knowledge on levels and trends of morbidity and mortality, the emphasis of this paper should be more towards concepts, methods, and data deficiencies. In Section 1, we set out definitions and frameworks for considering health problems and health research; we review recent conceptual models for the analysis of the determinants of child survival; and we outline a framework, focusing on modifiable determinants of health and life-cycle health effects, which is used in subsequent sections. In Section 2, relationships between national and societal level determinants and health are reviewed and then set aside. In Section 3, we review available data on world patterns and trends of morbidity and mortality, highlighting the data deficiencies and lacunae. In Section 4, we follow the life of a woman in a developing country and examine the health problems, and their determinants, which she and her children face. In Section 5, we draw these strands together and, having reviewed current approaches to prioritizing health problems and suggested some ways in which they could be improved, in Section 6 identify several research priorities, emphasizing the need for methodological research. This paper was commissioned in March 1987; prepared in draft and presented to a meeting at Chateau de Bossey, Geneva, Switzerland during 15-17 July; and revised and completed in September 1987. It is in no sense definitive or final.(ABSTRACT TRUNCATED AT 400 WORDS)

Disability from dracunculiasis: effect on mobility

A study was conducted in northeastern Imo State to define the disability and restriction of mobility associated with dracunculiasis. The study was part of an evaluation of the UNICEF-assisted Drinking Water Supply and Sanitation Project in Imo State, Nigeria. A sample of household units (100 in year 1, 195 in year 2) was visited every two weeks to determine who was affected by dracunculiasis and to characterize the extent of related disability. The average duration of symptoms was 12.7 weeks (range 3-29 weeks). Fifty eight per cent of all episodes of disease resulted in severe disability (with the individual unable to leave the compound) lasting a mean of 4.2 weeks (range 2-12). The mean period of severe disability was significantly higher for those aged 50 years and over than for those less than 50 years old. In the area studied, the disease occurred during the peak yam and rice harvest time and the period of preparation for the planting season. This is the first study to document systematically and prospectively the marked restriction of normal activity in affected individuals and the long duration of the disability. These findings can assist in improving estimates of the costs associated with dracunculiasis and of potential economic benefits if the disease were eradicated.

Infant feeding and risk of severe diarrhoea in Basrah city, Iraq: a case-control study

A case-control study of the relationship between feeding mode and risk of hospitalized diarrhoea in infants (aged 2-11 months) in Basrah city was conducted between September 1983 and May 1984. A total of 597 cases were recruited from among infants admitted with diarrhoea to the major paediatric hospital in the city, while 723 controls were recruited from among healthy infants attending any of the seven maternal and child health clinics in Basrah. A variety of potentially confounding variables were controlled in the analysis. For infants aged 2-5 months, breast-feeding alone or breast-feeding plus food were the least risky feeding modes. Bottle-feeding was dangerous and bottle-feeding alone was associated with a risk of 55 among infants aged 2-3 months, and 37 among infants aged 4-5 months, relative to exclusive breast-feeding. For older infants (6-11 months), the risks of hospitalized diarrhoea were not significantly different among different partial breast-feeding modes, but non-breastfeeding was dangerous, especially exclusive bottle-feeding. Food intake was associated with a reduced risk of severe diarrhoea among bottle-fed infants but not with an increased risk among breast-fed infants. Among bottle-fed infants, no association was found between risk of severe diarrhoea and method of bottle-cleaning. Previous breast-feeding conferred no current protection.

Epidemiology and tropical public health: current and future contributions with particular emphasis on the role of the London School of Hygiene and Tropical Medicine

This paper presents a forward look at the contribution of epidemiology to public health in developing countries and pays particular attention to the present and future role of the London School of Hygiene and Tropical Medicine. Three types of epidemiology are distinguished for the purposes of the paper: micro-epidemiology, desk epidemiology and macro-epidemiology. Micro-epidemiology, the application of epidemiology to particular health problems in particular settings, is illustrated through examples in both child and adult health. More emphasis on acute respiratory infections in children, maternal and neonatal health, and adult health in general is advocated. The contributions of desk epidemiology are illustrated through examples of the exploration of the effects of confounding and mis-classification. Continued attention to theoretical and methodological issues is essential if the quality and cost-effectiveness of field studies are to continue to improve. Macro-epidemiology is concerned with the absolute and relative contributions of particular causes or diseases to the overall burden of ill-health in a population. It is a young field in which important advances may be made in the 1990s. Its results are highly relevant to policy making and resource allocation in the health sector. In conclusion, the relationship between epidemiologists in developed and developing countries is briefly discussed and some recommendations are made.

The bacteriological quality of traditional water sources in north-eastern Imo State, Nigeria

Monthly bacteriological water testing of traditional water sources (ponds, rivers, unprotected springs and traditional wells) used by five villages in northeastern Imo State, Nigeria, was conducted during the period January 1983 to August 1985. The membrane-filtration technique was used to detect faecal coliforms (FC) and faecal streptococci (FS). Evidence of faecal pollution was seen throughout the year for all water sources. During the study period, the monthly geometric mean counts per 100 ml of water (all sources combined) ranged from 760 to 17877 for FC and from 678 to 17394 for FS. The peak period of faecal pollution occurred during the transition between the dry and wet seasons and in the early wet season. During this peak pollution season (February-May), the geometric mean counts were 2.5-7.2 times higher than in the remaining part of the year for all source types except rivers, with ponds being the most heavily polluted. Preliminary findings on the sensitivity and specificity, in this tropical environment, of the standard membrane-filtration technique for enumerating FC are presented. The implications of the findings of this study for the environmental control of waterborne and hygiene-related diseases are discussed.

The epidemiology of acute diarrhoea in a rural community in Imo State, Nigeria

As part of an evaluation of a water supply and sanitation project, a baseline cross-sectional study of diarrhoea, and its putative risk factors, was conducted in 5 villages in Imo State, Nigeria. Data were collected from 4641 and 5920 persons during surveys in the dry and wet seasons, respectively. 8 d period prevalence rates for diarrhoea ranged from 5 to 50%, with the highest rates occurring in the 6 to 23 month age group. Diarrhoea was associated with up to 75% of all illnesses in young children and with about 20% in adults. Risk factors included lower socio-economic status, an unclean domestic environment, use of non-purified water, absence of soap, and feeding methods other than exclusive breast-feeding in the early months of infancy. These results suggest that the education component of water supply and sanitation projects should emphasize personal and domestic hygiene and infant feeding.

Feeding and nutritional status among infants in Basrah City, Iraq: a cross-sectional study

Feeding histories were collected on 772 randomly selected infants visiting Maternal and Child Health Clinics in Basrah city between October 1983 and May 1984. Weight-for-age data on 557 of these infants (72 per cent) were also obtained. Over 90 per cent of infants were breast-fed initially, and prevalence rates of breast-feeding during infancy were higher among infants of low socioeconomic status (LSES) than those of high socioeconomic status (HSES). Exclusive breast-feeding declined sharply during the first 6 months of life. Supplementation of breast-feeding with bottle-feeding was common, especially among HSES infants. Methods of cleaning infant feeding bottles were more hygienic among HSES than LSES families. Comparison of the weight-for-age of infants on different feeding modes in the 2-7 months age group showed that exclusively breast-fed infants were slightly, but significantly, heavier than partially breast-fed or non-breast-fed infants. Mild faltering of weight-for-age with age was observed, relative to the NCHS median reference weight.

Comparison of five assays for the heat-labile enterotoxin of Escherichia coli

Enzyme-linked immunosorbent assay (ELISA), DNA-DNA hybridisation, Vero cell assay, the Biken test and a new membrane-filter method were compared in the detection of heat-labile enterotoxin (LT) of Escherichia coli. Six subcultures of each of 50 strains of E. coli from the Biken collection were evaluated "blind" in the laboratory. The combined results of the most reproducible tests (ELISA and DNA-DNA hybridisation) were used to calculate the sensitivity and specificity of the other assays. The Vero-cell assay had a high sensitivity (98%) but a lower specificity (91%). The Biken and membrane-filter assays had sensitivities of 58-71% and 77-84% respectively, depending on the type of antiserum used. Only one false positive result was obtained with the Biken test; specificity of the membrane-filter assay was 94-95%. The membrane-filter assay, with anti-cholera toxin, is specific and reasonably sensitive. It has particular advantages over DNA-DNA hybridisation and the Biken test, and it may prove suitable for screening large numbers of E. coli isolates in epidemiological studies in developing countries.

The effects of distance and season on the use of boreholes in northeastern Imo State, Nigeria

A study was conducted in a rural area of northeastern Imo State to examine the effect of distance and season on the use of boreholes, provided at a borehole-to-population ratio of 1 to 440. The type of water source used by households varied according to season. In the water-scarce dry season, 98% of households used borehole water: 64% as their sole source, a further 26% as their main source, and 8% as a secondary source. The use of borehole water as the main source was little influenced by distance until the household-to-borehole distance reached approximately 2 km. The situation was different in the wet season when the availability of water sources was much greater. In this season, rainwater was the main water source for 64% of households. Borehole water was the main source for only 31% of households. In the rainy season, the use of borehole water as the main source showed a significant decrease with increasing household-to-borehole distance. The provision of one borehole for 400-500 people was associated with a high rate of use as the main water source only in the dry season. However, the use of boreholes as either a main or alternative source was high in both seasons and it is possible that those households that used boreholes as an alternative source used the water for drinking.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane filter assay for detection of enterotoxigenic Escherichia coli in epidemiological studies

A membrane filter assay is described for detection of heat-labile toxin (LT) production by Escherichia coli. Bacterial colonies were isolated on a membrane filter which was then incubated on an agar medium containing anti-cholera toxin. LT produced by bacterial colonies diffused through the membrane filter, complexed with the antiserum, and formed a zone of precipitation in the agar. Requirements for reagents and materials were simple. The membrane filter assay showed good agreement with both the ganglioside-enzyme-linked immunosorbent assay and the DNA-DNA hybridisation assay and may prove to be an important technique for the study of the epidemiology of enterotoxigenic E coli in developing countries.

The impact of physico-chemical stress on the toxigenicity of Vibrio cholerae

The expression of toxigenicity by Vibrio cholerae, before and after exposure to various conditions of salinity, pH and cation composition and concentration, has been measured. Exposure to these conditions did not select for hyper- or hypo-toxigenic strains. This suggests that toxigenic V. cholerae O1 are unlikely to lose their toxigenicity when exposed to environmental stress and that V. cholerae toxin production is not a response to the stresses included in this study. These results are consistent with an aquatic reservoir for toxigenic V. cholerae O1.

Interventions for the control of diarrhoeal diseases among young children: prevention of low birth weight

The effect of low birth weight (LBW) on diarrhoea morbidity and mortality is analysed and interventions to increase birth weights are reviewed. Birth weight is a major determinant of infant mortality and, in developed countries at least, its effect on neonatal mortality is independent of socioeconomic status. We have located no satisfactory data on LBW as a determinant of diarrhoea mortality or morbidity. The strong association between LBW and mortality, however, makes it likely that there is an association between LBW and diarrhoea mortality in developing countries where diarrhoea is a major cause of infant death. Poor maternal nutrition, certain infections, pre-eclampsia, arduous work after mid-pregnancy, short birth intervals, and teenage pregnancy are likely to be causally associated with LBW in developing countries. Tobacco and alcohol consumption are additional risk factors.Of the interventions examined, maternal food supplementation has been the most studied. If targeted to mothers at nutritional risk, and if the food is consumed in addition to the usual diet, the prevalence of LBW can be expected to be reduced. However, food supplementation can be expensive and the results from carefully supervised feeding trials may be better than those that can be achieved in national programmes. The effect of supplementation with iron, zinc or folate requires further study. If it were possible to intervene in maternal nutrition, health and life-style in a developing country in a way that reduced the prevalence of LBW from around 30% to around 15%, a fall in the infant mortality rate of around 26% would be expected. The fall in infant diarrhoea mortality rate might be similar. The scarce data on relative risk of morbidity by birth weight do not allow any comparable computations for morbidity reductions to be made.This review confirms that whatever its association with diarrhoea, LBW is an important determinant of infant mortality. For the more general goal of reducing infant mortality it is necessary to know more about the nature, etiology, and prevention of LBW in developing countries.

Interventions for the control of diarrhoeal diseases among young children: chemoprophylaxis

A number of situations place young children at increased risk of diarrhoea. Among these, the best documented in developing countries is contact with a diarrhoea case in a family or household. The most common application of chemoprophylaxis in developing countries is to prevent cholera or shigellosis among household contacts of known cases. There is little evidence that chemoprophylaxis is effective in reducing diarrhoea morbidity and mortality, except perhaps in travellers. Theoretical calculations in this paper (based on optimistic assumptions) suggest that chemoprophylaxis of household contacts of known cholera cases in Bangladesh might reduce overall diarrhoea incidence rates in children under 5 years of age by 0.02-0.06% and diarrhoea mortality rates by 0.4-1.2%. Chemoprophylaxis of household contacts of known shigellosis cases might reduce overall diarrhoea incidence rates by 0.15-0.35% and diarrhoea mortality rates by 0.3-0.7% in the same age group. The correct identification of index cases of cholera and shigellosis, followed by the rapid distribution of drugs to their household contacts, requires skills and resources that are scarce in the developing countries. Chemoprophylaxis can contribute to the widespread emergence and dissemination of antimicrobial resistance. The available evidence suggests that chemoprophylaxis is not feasible in many settings and that, even if successfully implemented, it is not a cost-effective intervention for national diarrhoeal diseases control programmes.

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

A theoretical model is proposed that relates the level of ingestion of diarrhoea-causing pathogens to the frequency of diarrhoea 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 of a low infectious dose. The impact of water supply and sanitation on diarrhoea, related infections, nutritional status, and mortality is analysed by reviewing 67 studies from 28 countries. The median reductions in diarrhoea morbidity rates are 22% from all studies and 27% from a few better-designed studies. All studies of the impact on total mortality rates show a median reduction of 21%, while the few better-designed studies give a median reduction of 30%. Improvements in water quality have less of an impact than improvements in water availability or excreta disposal.

Response of toxigenic Vibrio cholerae 01 to physico-chemical stresses in aquatic environments

The survival and growth of toxigenic Vibrio cholerae 01 in water under various conditions of salinity, pH, temperature and cation composition and concentration were studied in an extensive series of laboratory experiments. Inter- and intra-strain variation in stress response (of 01 and non-01 strains) and the ability of V. cholerae to adapt to stressful environments were also studied. Toxigenic V. cholerae 01 were able to survive for at least 70 days at 25 degrees C in solutions of sea salt. The optimal salt concentration was 2.0% though all solutions in the range 0.25-3.0% gave good support. Substrains with enhanced capacity to persist at sub-optimal salinity (0.1%) were demonstrated. A great degree of inter-strain variation in stress response at low salinity (0.05%) was found among 59 strains, and this variation was unrelated to serogroup (01 or non-01), source (clinical or environmental) or country of origin (Tanzania or Bangladesh). At optimal salinity, inter-strain variation was less and 18 out of 20 strains remained viable at high concentrations for at least 40 months at 25 degrees C. V. cholerae 01 could not survive beyond 45 days at 4 degrees C and optimal salinity, either with or without nutrients. The optimal pH range for survival at 25 degrees C was 7.0-8.5 at optimal salinity, and 7.5-9.0 at low salinity. V. cholerae 01 require Na+ for survival in the absence of nutrients, and for enhanced growth in their presence. The presence of Ca2+ or Mg2+, in addition to Na+, further enhanced survival. These, and other results reported in this paper, suggest that toxigenic V. cholerae 01 are able to survive for extended periods in warm water containing no nutrients but having a salinity of 0.25-3.0% and a pH of around 8.0. With added nutrients and under the same conditions, rapid growth is possible. The implications of these findings for the identification of putative aquatic reservoirs of V. cholerae 01, and for the epidemiology of cholera, are considerable.

Measuring the impact of water supply and sanitation investments on diarrhoeal diseases: problems of methodology

A review of the published literature on the impact of water supply and/or excreta disposal facilities on diarrhoeal diseases, or on infections related to diarrhoea, reveals several methodological problems that hamper the drawing of definitive conclusions from these studies. This paper examines eight of these methodological problems: lack of adequate control, the one to one comparison, confounding variables, health indicator recall, health indicator definition, failure to analyse by age, failure to record usage, and the seasonality of impact variables. It is suggested that an evaluation of the impact on health of environmental interventions may best be undertaken by the combined efforts of engineers, social scientists and epidemiologists in 'opportunistic' settings and that the intervening behavioural processes so necessary for health impact to occur should be a primary focus of such evaluations.