Globally, around 2.4 million deaths (4.2% of all deaths) could be prevented annually if everyone practised appropriate hygiene and had good, reliable sanitation and drinking water. These deaths are mostly of children in developing countries from diarrhoea and subsequent malnutrition, and from other diseases attributable to malnutrition.
How is an opportunity to prevent so many deaths (and 6.6% of the global burden of disease in terms of disability-adjusted life years or DALYs failing to attract the attention of the international public health community?
In this introductory paper to the PLoS Medicine series on water and sanitation, we develop the idea that these basic needs are the forgotten foundations of health.
A Massive Disease Burden Is Associated with Deficient Hygiene, Sanitation, and Water Supply
While rarely discussed alongside the “big three” attention-seekers of the international public health community—HIV/AIDS, tuberculosis, and malaria—one disease alone kills more young children each year than all three combined. It is diarrhoea, and the key to its control is hygiene, sanitation, and water (HSW).
Regrettably, it is no surprise that much ill health is attributable to a lack of HSW. Globally, nearly one in five people (1.1 billion individuals) habitually defecates in the open. Conversely, 61% of the world's population (4.1 billion people) has some form of improved sanitation at home—a basic hygienic latrine or a flush toilet. Between these two extremes, many households rely on dirty, unsafe latrines or shared toilet facilities. Not only can it prevent endemic diarrhoea, adequate sanitation can help to prevent intestinal helminthiases, giardiasis, schistosomiasis, trachoma, and numerous other globally important infections.
The situation for drinking water appears better than that for sanitation. Although around 13% of the world's population (884 million people) lives in households where water is collected from distant, unprotected sources, 54% (3.6 billion) receives piped water at home. However, many piped water systems in developing and middle income countries work for only a few hours per day and/or are unsafe. In larger Asian cities, for example, more than one in five water supplies fails to meet national water quality standards. Reliable safe water at home prevents not only diarrhoea but guinea worm, waterborne arsenicosis, and waterborne outbreaks of diseases such as typhoid, cholera, and cryptosporidiosis.
Much of the impact of water supply on health is mediated through increased use of water in hygiene. For example, hand washing with soap reduces the risk of endemic diarrhoea, and of respiratory and skin infections, while face washing prevents trachoma and other eye infections. A recent systematic review of the literature confirmed that hygiene, particularly hand washing at delivery and postpartum, also helps to reduce neonatal mortality. It might be argued that water supplies also make flush toilets feasible, but this does not necessarily add to their health benefits, as we have seen no credible evidence that the health benefits of sanitation cannot be achieved by dry latrines, if they are properly built and maintained.
This Disease Burden Is Largely Preventable with Proven, Cost-Effective Interventions
A balanced interpretation of the available evidence suggests that a reasonably well-implemented intervention in one or more of hygiene, sanitation, water supply or water quality, where preexisting conditions are poor, is likely to reduce diarrhoeal disease prevalence by up to a third. Still greater reductions (up to 63%) are associated with water piped to one or more taps on a property. Such a major impact merits far more attention from health professionals and health systems than has been common in recent decades.
We are still learning about the role of HSW in disease control. For example, Ascaris and other intestinal worms are known to be associated with poor sanitation, but a recent review found evidence that hand washing with soap can also help to prevent transmission of ascariasis. We know that trachoma is prevented by facial hygiene and hand washing, but recent research has also highlighted the role of latrines in controlling the Musca sorbens flies that carry the Chlamydia pathogen between children's faces. Even regarding the effect of hygiene on diarrhoea among young children in poor communities, we still have much to learn. There is good evidence to justify promotion of hand washing with soap, but for other aspects of hygiene behaviour, such as proper disposal of children's stools, the epidemiological evidence is from observational studies, which are subject to confounding.
The most effective means of promoting behaviour change is also a fruitful research field. It has only recently become clear to health professionals that emotional levers (“Clean hands feel good”) change people's health behaviours more effectively than cognitive statements (“Dirty hands cause disease”). Advertising agencies have known this for years. They also know the importance of investing in formative research, testing, and evaluation, to tailor the messages to local people's beliefs and aspirations. If health workers can divest themselves of the unsubstantiated belief that health considerations motivate behaviour, they can become a more effective force for hygiene behaviour change.
There are alternative ways to tackle some of the HSW-associated disease burden. The widespread introduction of oral rehydration therapy (ORT) in the 1980s, for example, contributed much to reducing mortality from diarrhoeal disease. However, such interventions focus on mortality rather than morbidity and on secondary rather than primary prevention. Moreover, ORT does not address the problems of persistent diarrhoea and dysentery.
It is sometimes claimed that the lack of an overall decline in diarrhoea morbidity rates despite increasing coverage with water and sanitation shows that the health benefits of HSW are illusory. However, there are other possible explanations for the apparent contradiction. First, coverage has not advanced as rapidly as one would wish, or as some official figures suggest. Second, the diarrhoea morbidity data are subject to a variety of interpretations; for example, reviews have found that apparent geographical variations could be explained by differences in study design. Third, if challenge by diarrhoea pathogens can cause tropical enteropathy without diarrhoea, a reduction in that challenge could reduce mortality risk without necessarily reducing diarrhoea morbidity.
In fact, the benefits to health of improving HSW are far greater than implied by disease-specific statistics. In the early 1900s, sanitary engineers in the US and Germany identified the “Mills-Reincke phenomen.