This study assesses the effect of drinking water quality on diarrheal disease in good and poor sanitary conditions using a random sample of 2,355 Filipino infants over the first year of life. The study provides powerful confirmation of the importance of environmental factors on diarrhea: The effects of water quality, household sanitation, and community sanitation are strong, consistent, and statistically significant. The positive impact of improved water quality is greatest for families living under good sanitary conditions, with the effect statistically significant when sanitation is measured at the community level but not significant when sanitation is measured at the household level. Improving drinking water quality would have no effect in neighborhoods with very poor environmental sanitation; however, in areas with better community sanitation, reducing the concentration of fecal coliforms by two orders of magnitude would lead to a 40 percent reduction in diarrhea. Providing private excreta disposal would be expected to reduce diarrhea by 42 percent, while eliminating excreta around the house would lead to a 30 percent reduction in diarrhea. The findings suggest that improvements in both water supply and sanitation are necessary if infant health in developing countries is to be improved. They also imply that it is not epidemiologic but behavioral, institutional, and economic factors that should correctly determine the priority of interventions.

The promotion of proper infant feeding practices and the improvement of environmental sanitation have been two important strategies in the effort to reduce diarrhoeal morbidity among infants. Breast-feeding protects infants by decreasing their exposure to water- and foodborne pathogens and by improving their resistance to infection; good sanitation isolates faecal material from the human environment, reducing exposures to enteric pathogens. Taken together, breast-feeding and good sanitation form a set of sequential barriers that protect infants from diarrhoeal pathogens. As a result, breast-feeding may be most important if the sanitation barrier is not in place. This issue is explored using data from a prospective study of 2355 urban Filipino infants during the first 6 months of life. Longitudinal multivariate analyses are used to estimate the effects of full breast-feeding and mixed feeding on diarrhoeal disease at different levels of sanitation. Breast-feeding provides significant protection against diarrhoeal disease for infants in all environments. Administration of even small portions of contaminated water supplements to fully breast-fed infants nearly doubles their risk of diarrhoea. Mixed-fed and weaned infants consume much greater quantities of supplemental liquids, and as a result, the protective effect of full breast-feeding is greatest when drinking-water is contaminated. Similarly, full breast-feeding has stronger protective effects among infants living in crowded, highly contaminated settings.

Storing drinking water in the home is common in the developing world. Several studies have documented increased concentrations of fecal coliforms during household storage. This has led to the belief that in‐house water contamination is an important transmission route for enteric pathogens and, moreover, that improving water source quality is not warranted until that quality can be maintained in the home. We contend that in‐house water contamination does not pose a serious risk of diarrhea because family members would likely develop some level of immunity to pathogens commonly encountered in the household environment. Even when there is no such immunity, transmission of these pathogens via stored water may be inefficient relative to other household transmission routes, such as person‐to‐person contact or food contamination. A contaminated water source poses much more of a risk since it may introduce new pathogens into the household, The effects of water source and in‐house contamination on diarrheal disease are estimated for 2355 Filipino infants. The results confirm our hypothesis: contaminated water sources pose a serious risk of diarrhea while contamination of drinking water in the home does not. Water boiling is shown to eliminate the risk of diarrhea due to water source contamination. The results imply that improvements in water source quality are more important than improving water storage practices.

This study examines determinants of growth from birth to 24 months in a sample of approximately 3000 urban and rural Filipino children. Individual, household, and community data were collected bimonthly during the Cebu Longitudinal Health and Nutrition Survey. Separate longitudinal, multivariate models were used to identify determinants of weight in children from birth to 6 months and 6-24 months of age. Previous weight, male gender, mother's height, and season of the year showed significant positive associations with weight in all models. Full and mixed breast-feeding significantly increased weight, but the effects of breast-feeding declined as children got older. Breast-feeding had a direct growth-enhancing effect in addition to its indirect effect through the prevention of diarrheal morbidity. Detrimental effects of recent diarrheal morbidity were particularly important in the older age group, but these effects were mitigated by breast-feeding. Since infant feeding variables are included in the models, the results strongly suggest an effect of diarrheal morbidity on growth independent of its known effects on infant feeding and dietary intake. Febrile respiratory infections had important detrimental effects on weight in both age groups.

The effect of behaviour on health is a major area of contemporary epidemiological enquiry. Most epidemiological studies of the effect of behaviour on health assume that the levels of the behaviour-related variables are determined by factors other than those under study. However, in many instances, obvious examples are breastfeeding and smoking, not only do behaviours affect health but, conversely, individuals take into account their (observable and non-observable) health conditions when making behavioural decisions. In models which allow for the joint determination of health and behaviour, both health and behavioural variables are 'endogenous', that is, determined by forces acting within the model. Through some simple didactic examples it is shown that estimates of the effect of behaviour on health are biased if endogeneity is ignored. Review of the small empirical literature on this subject shows perverse results, such as a negative relationship between the use of prenatal care and infant mortality, when endogeneity is ignored. Standard procedures for taking account of the effects of endogeneity are described briefly.

This study used a unique longitudinal survey of more than 3000 mother-infant pairs observed from pregnancy through infancy. The sample is representative of infants from the Cebu region of the Philippines. The sequencing of breast-feeding and diarrheal morbidity events was carefully examined in a longitudinal analysis which allowed for the examination of age-specific effects of feeding patterns. Because the work controlled for a wide range of environmental causes of diarrhea, the results can be generalized to other populations with some confidence. The addition to the breast-milk diet of even water, teas, and other nonnutritive liquids doubled or tripled the likelihood of diarrhea. Supplementation of breast-feeding with additional nutritive foods or liquids further increased significantly the risk of diarrhea; most benefits of breast-feeding alone or in combination with nutritive foods/liquids became small during the second half of infancy. Benefits of breast-feeding were slightly greater in urban environments.

This study had 2 objectives: 1) to determine whether a case-control approach is an effective measure for assessing the effect of improved sanitation on bacterial diarrhea, and 2) to assess the effects of environmental sanitation on diarrheal disease in Cebu. The study took place during the warm, rainy months (July-September) of 1985. The study population consisted of 281 children under 2 who were treated at 1 of 16 clinics for diarrhea due to Escherichia coli, salmonella, shigella, and Vibrio cholerae. The controls were 384 children under 2 who were brought to the clinics for respiratory ailments and did not have diarrhea. Environmental sanitation was classed as "good" if the bacterial count in the water supply was low (i.e., water was obtained from the municipal water supply or bore holes) and if excreta disposal was adequate (i.e., there were flush toilets, sealed latrines, or pit latrines). Water quantity was measured by the number of times the child was bathed. The effects of the exposure variables on the study children were determined by logistic regression analyses adjusted for confounding variables, which included sex, educational level of the household, breast feeding, attendance at well-baby clinics, number of children under 5 in the household, and frequency of bathing the child. The results of the study showed that improved sanitation reduced the episodes of bacterial diarrhea by 40%, and that case-control studies with sample sizes of about of about 500 cases and 500 controls are adequate to detect disease reductions of 33% or more.

The problems and prospects in the use of case-control studies to assess the effects of improvements in environmental sanitation on diarrhoea morbidity are discussed on the basis of two field studies. It is concluded that an adequate design is available for assessing the effects of a single improvement on diarrhoeal disease. The estimates of effect appear to be valid and sufficiently precise. For addressing more complex questions of interactions, sample sizes would have to be increased substantially. The experience with two field studies suggests that there is hope that a simpler protocol may be feasible, in which only limited information is collected, in which few home visits are made, and in which analytical techniques are simple. Until more field studies have been conducted definitive conclusions cannot be reached on the applicability of such a simple, rapid and inexpensive approach.

A case-control design has been applied in the evaluation of improved environmental sanitation on diarrhoeal diseases in rural Malawi. The study demonstrates the feasibility of using such an approach to evaluate two levels of water supply and sanitation service quickly and at moderate cost. Sample sizes would need to be increased substantially to evaluate multiple levels of service or to investigate interactions between water supply and sanitation. The results indicate that children living in families who use good quality water supplies and latrines experience 20% less diarrhoea as reported to the health clinics during the warm, rainy season.