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Some global statistics for water and sanitation related disease

Author: Sarah Parry-Jones and Pete Kolsky

Reviewed and Updated: Lucy Smith, June 2005

Quality assurance: Sandy Cairncross

The Global Burden of Diarrhoeal Diseases

Diarrhoea causes 2.5 million deaths/year, accounting for around 21% of all-cause mortality for children under five years old in developing countries (Kosek, 2003). This is equivalent to one child dying every twelve seconds, or a jumbo jet full of children crashing every 90 minutes.

In addition, diarrhoea accounts for the annual loss of around 62 million DALYs (disability-adjusted life years), a standard measure of the burden of disease calculated from the number of years of productive life lost due to illness and premature mortality (WHO, 2004); this figure provides an indication of the substantial socio-economic impacts of diarrhoeal diseases through loss of work, disrupted school attendance and medical costs. To put it into perspective, malaria leads to a loss of 47 million DALYs and tuberculosis 35 million DALYs per year (WHO, 2004).

The Role of Water, Sanitation and Hygiene Promotion

Interventions to improve water, sanitation, and hygiene practices have been shown to reduce sickness from diarrhoea by between a quarter and a third (Esrey et al, 1991; Fewtrell et al, 2005), although almost all diarrhoea deaths are potentially attributable to inadequate water, sanitation and hygiene (Pruss et al, 2002).

One of the main reasons that such interventions do not result in greater reductions in diarrhoeal disease and death is the complex web of pathways that can lead to the transmission of diarrhoea and other faecal-oral diseases (see Figure 1).

Figure 1: Transmission of disease from faeces

There is considerable debate over which class of intervention has the most health impact –sanitation, hygiene promotion, water supply or water quality. One point that is generally accepted, however, is that the supply of adequate quantities of water needs to be achieved before improvements in its quality can yield substantial benefits. This is because the organisms that cause diarrhoea can be spread through many routes besides drinking water, and the risk of transmission through these routes can be reduced by increased quantities of water for improved household and personal hygiene.

Another important factor limiting the reduction of diarrhoeal disease and mortality is the massively inadequate coverage of improved water supply and sanitation facilities in developing countries. An estimated 2.6 billion people lack adequate sanitation and 1.1 billion people are without access to safe water (WHO/UNICEF, 2004).

Such numbers explain the reasons behind the Millennium Development Goal (MDG) to halve the number of people without access to improved water and sanitation facilities by 2015. Although progress towards achieving this for water supply appears to be on track, improvements in sanitation coverage are much further behind; without accelerated progress, the sanitation target will be missed by a magnitude of half a billion people (WHO/UNICEF, 2004).

A considerable investment of US$11.3 billion/year is needed to reach the MDG drinking water and sanitation target by 2015. However, payback from increased productivity and earnings is predicted to be US$84 billion/year, based on calculations of time savings, increased school and work attendance and reduced health care costs (Hutton & Haller, 2004).

Other Water-Related Diseases

It is important to note that a wide range of diseases are related to (inadequate) water and sanitation in addition to diarrhoea, each of which also contributes significantly to the global burden of disease:

Intestinal worms

Approximately one half of the population of the developing world is infected with intestinal worms such as Ascaris, Trichuris and hookworm with an estimated one billion cases of each. These parasites can lead to malnutrition, anaemia, and retarded growth and cognitive abilities depending upon the severity of the infection (Chan, 1997).

All are spread due to contamination of the environment with faeces containing parasite eggs. These are then transmitted to a new host either through ingestion of soil or uncooked vegetables (Trichuris, Ascaris), or via penetration of the skin (hookworm). Hence improved sanitation and domestic hygiene present effective control measures (Esrey et al, 1991).

Trachoma

Trachoma is the leading cause of preventable blindness worldwide – an estimated 6 million people are already blind and a further 148 million suffer from active infections, which if left untreated result in gradual deterioration of vision (Emerson et al, 2004).

Transmission is via contact with discharge from the eyes of an infected person; a 25% reduction of trachoma can be achieved through provision of an adequate water supply for increased personal hygiene practices (Esrey et al, 1991), and improved sanitation has been shown to lower levels by 30% through reduction in fly populations which act as vectors for the infective agent and which breed in scattered human faeces (Emerson et al, 2004).

Schistosomiasis

Schistosomiasis affects 200 million people worldwide, with 20 million suffering severe consequences such as anaemia, impaired growth, poor cognition, and substandard school performance. Potential long-term effects include bladder cancer and serious kidney, liver or spleen complications.

The parasites enter water from faeces and urine and, after a short development period in a freshwater snail, are able to infect new human hosts by penetrating the skin; schoolchildren are particularly at risk through playing in water.

Esrey et al. (1991) in reviewing epidemiological studies, found a median 77% reduction of schistosomiasis from well-designed water and sanitation interventions which prevent faeces and urine from entering surface water.

Guinea Worm

Guinea worm infection causes a debilitating disease (dracunculiasis) characterised by a painful ulcer on the lower limbs from which the female adult worm slowly emerges. Although the disease is rarely fatal, it has strong socioeconomic impacts due to decreased agricultural productivity and income generation.

Dracunculiasis is the only disease exclusively transmitted by drinking water. Larvae released into water from a symptomatic patient are ingested by small crustaceans (Cyclops) which then infect a new host when swallowed in drinking water. Control is through safe water supply and/or filtration, health education and case management.

The global eradication initiative has made dramatic progress with the number of new cases reported per year dropping by almost 99% from 890,000 in 1989 to less than 16,000 in 2004 (WHO, 2005). Of the 11 remaining endemic countries across sub-Saharan Africa, 91% of these cases were in Ghana and Sudan. Pakistan, India and Senegal have recently been certified as "guinea worm free", with Cameroon, Chad, Central African Republic, Kenya and Uganda in pre-certification phase.

Note on Statistics

It is important to note that all statistics relating to global health and disease (including those given in this document) can only be approximations due to the many logistical issues involved in collecting data on such a large scale and under the conditions that exist in developing countries. Nonetheless, such figures still play a vital role in drawing attention to the relative magnitude and importance of world health issues

Sources and References

· Cairncross, S., Muller, R., Zagaria, N. (2002) Dracunculiasis (Guinea worm disease) and the eradication initiative. Clinical Microbiology Reviews, 15(2): 223-46

· Chan, M.S. (1997). The global burden of intestinal nematode infections – fifty years on. Parasitology Today 13(11): 438-443.

· Emerson, P.M., Lindsey, S.W., Alexander, N., Bah, M., Dibba, S.M., Faal, H.B. et al (2004). Role of flies and provision of latrines in trachoma control: cluster-randomised controlled trial. Lancet 363: 1093-1098.

· Esrey, S.A., Potash, J.B., Roberts, L., Shiff, C. (1991). Effects of improved water supply and sanitation on ascariasis, diarrhoea, dracunculiasis, hookworm infection, schistosomiasis, and trachoma. Bull. WHO 69(5): 609-621.

· Fewtrell, L., Kaufmann, R.B., Kay, D., Enanoria, W., Haller, L., Colford, J.M. (2005). Water, sanitation and hygiene interventions to reduce diarrhoea in less developed countries: a systematic review and meta-analysis. Lancet Infectious Diseases 5: 42-52.

· Hutton, G., Haller, L. (2004). Evaluation of the costs and benefits of water and sanitation improvements at the global level. WHO, Geneva.

· Kawata, K. (1978). Water and other environmental interventions - the minimum investment concept. American Journal of Clinical Nutrition 31: 2114-2123.

· Kosek, M., Bern, C., Guerrant, R.L. (2003). The global burden of diarrhoeal disease, as estimated from studies published between 1992 and 2000. Bull. WHO 81(3): 197-204.

· Pruss, A., Kay, D., Fewtrell, L., Bartram, J. (2002). Estimating the burden of disease from water, sanitation and hygiene at a global level. Environmental Health Perspectives 110(5): 537-542.

· WHO (2004). World Health Report 2004 – Changing History. WHO, Geneva.

· WHO (2005) Dracunculiasis eradication: global surveillance summary 2004. Weekly Epidemiological Record 80(19): 165-176.

· WHO/UNICEF (2004). Meeting the MDG drinking water and sanitation target: a mid-term assessment of progress. WHO/UNICEF Joint Monitoring Programme for Water Supply and Sanitation (www.unicef.org/publications/index_23223.html).

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