Chapter 16 Unsafe water , sanitation and hygiene

The disease burden from unsafe water, sanitation and hygiene (WSH) is estimated at the global level taking into account various disease outcomes, principally diarrhoeal diseases. The risk factor is defined as including multiple factors, namely the ingestion of unsafe water, lack of water linked to inadequate hygiene, poor personal and domestic hygiene and agricultural practices, contact with unsafe water, and inadequate development and management of water resources or water systems. For estimating disease burden of infectious diarrhoea, exposure scenarios are established according to water supply and sanitation infrastructure, the level of faecal–oral pathogens in the environment and populations assigned to these scenarios. The total burdens from schistosomiasis, trachoma, ascariasis, trichuriasis and hookworm disease are all wholly attributable to unsafe WSH and have been quantified at global level as an additional exercise. Unsafe WSH is an important determinant in a number of additional diseases, such as malaria, yellow fever, filariasis, dengue, hepatitis A and hepatitis E, typhoid fever, arsenicosis, fluorosis and legionellosis, some of which present a high disease burden at global level. For infectious diarrhoea, six exposure levels were defined, with the lowest risk level corresponding to an ideal situation where WSH plays no role in disease transmission. Exposure prevalence, in terms of infrastructure, was determined from the Global Water Supply and Sanitation Assessment 2000. This assessment is a synthesis of major international surveys and national census reports covering 89% of the global population. The parameters considered included access to improved water sources and improved sanitation facilities. Relative risk estimates were based on reviews and large multi-country studies for areas with high faecal–oral pathogen loads in the environment (i.e. principally in developing countries). The proportion of disease Chapter 16