Contamination of water and food by faecal material as a result of poor sanitation and poor hygiene, leading to unsafe drinking water, is a major cause of gastrointestinal illness, particularly diarrhoea. Diseases and organisms associated with diarrhoea include cholera, typhoid, hepatitis A, giardia and cryptosporidium (Lozano et al. 2013).
The most important known viral cause of diarrhoea (rotavirus) is being reduced by vaccination programmes (Burnett et al. 2017). Open defecation also causes important parasitic diseases transmitted via contact with soil and water (e.g. ascaris, hookworm, water snails) (McCarty, Turkeltaub and Hotez 2014; Lo et al. 2017).
While hygiene-related diseases have diminished greatly, deaths from diarrhoea still constituted the second most prevalent cause of death (about 13 per cent) in children aged one to four years in 2010 (Lozano et al. 2013). Sub-Saharan Africa and South Asia have the highest mortality rates associated with water, sanitation and hygiene (WHO 2017a). Chronic gastrointestinal infections, including those from parasites, cause disability, economic loss and cognitive impairment (Pinkerton et al. 2016; Lo et al. 2017). Because freshwater provides a habitat for mosquito-breeding, malaria and dengue fever exhibit an even higher disease burden for individuals residing near such habitats, although the situation is slowly improving (e.g. through widespread bed net use) (Ebi et al. 2016; Hemingway et al. 2016). Recent estimates of the burden of disease due to diarrheal diseases are summarized in Figure 9.21.
Health effects from water and sanitation-related diseases appear to vary by gender. Women may have less access to sanitation compared with men and spend more time in environments where open defecation has occurred, thus incurring a greater risk of parasite exposure. Gendered roles of fetching water and caring for young children, including disposing of their faeces, may further increase the exposure of women to sources of infection. Nevertheless, a recent systematic review and meta-analysis found that, overall, infectious diarrhoea was more common in males. Schistosomiasis was also more common in men, but cholera was more frequent in women (Sevilimedu et al. 2016).
Predicted hydrologic cycle changes associated with climate change may exacerbate the environmental health-related diseases, particularly diarrhoea (GBD 2015 DALYs and HALE Collaborators 2016; Mukabutera et al. 2016; Musengimana et al. 2016; Thiam et al. 2017).