|GATE - 1/95 - Waste Water: Resource Management and Environmental Hygiene (GTZ GATE, 1995, 56 p.)|
Hygiene must have higher priority by Peter Weis
The outbreak of the cholera epidemic in Peru in January 1991, the first such epidemic on the American continent in the 20th century, drew public interest again to this classical pest which has plagued poor underprivileged people the world over for centuries. Such a cholera epidemic which attracts great attention by the media obstructs our view for the fact that even when there is no cholera, diarrhoeal diseases join acute respiratory diseases, measles, malaria and tuberculosis in being the major causes of sickness and death in developing countries.
World-wide, one infant in four of those dying under 5 years of age dies from a diarrhoeal disease. The vibrio cholerae pathogen only plays a minor role. Viruses, particularly rotavirus, are the main cause of diarrhoeal diseases, followed by bacterial pathogens and parasites (Table 1).
Causes of diarrhoeal diseases
· viruses: rota virus, adeno
virus, enterovirus (polio, coxsackie, etc.)
· bacteria: salmonella, shigella, yersinia, campylobacter, vibrio cholerae, pathogenic, E.coli
· parasites: entamoeba histolytica, giardia lamblia, cryptosporidium
Experience from history
Long-term monitoring of diarrhoeal diseases on a global scale shows that despite world-wide efforts, the estimated number of new cases per year remained constant at 1 billion cases annually between 1980 and 1990, although the annual diarrhoeal specific mortality in the same period fell from 4.6 million to 3.2 million (Bern et al. 1992). It can be concluded that c. 0.3 % of all patients with diarrhoeal diseases die from the disease. Morbidity and mortality rates are not evenly spread.
They cluster quite characteristically in children in their first years of life, reaching a maximum in infants aged 6 to 12 months (Table 2) who average 5 diarrhoeal episodes per year and in conditions of poverty and particularly susceptible groups such as pregnant women, malnourished and undernourished people and individuals with a compromised immune system (e.g. AIDS patients) .
Table 2: Estimated median diarrhoeal morbidity. For under-5-years old, based on the results from 18 studies in developing countries.
Since the 19th century, the public health sector and also water engineers around the world assumed that improving the quality of drinking water could make a significant contribution to reducing diarrhoeal discases and consequently raising the health status of the population (Kolsky, 1993). From the historical viewpoint this opinion was underlined by the work of John Snow on the cholera epidemic in London in 1854 (Hennekens, 1987).
Thirty years before Pasteur and Koch brought out their germ theories, Snow, a practising physician and epidemiologist, claimed that cholera was transmitted by contaminated water. He put forward impressive epidemiological data to prove this: People whose water came from the Southwark and Vauxhall Company, which pumped non-filtered river water from the Thames into the water supply system, were subject to eightfold the risk of dying from cholera than people whose water was pumped by the Lambeth Company, which took water upstream from London and passed it through sand filters.
Experience from the cholera epidemic in the German city of Hamburg in 1892 strikingly confirmed John Snow's findings: while Hamburg was hit by a cholera epidemic causing high mortality, the then neighbouring town of Altona which was already using sand filters was largely spared from the epidemic.
Indeed, improved drinking water supplies in London and Hamburg could have avoided many cholera-induced deaths; but this should not distract from the fact that most diarrhoeal diseases including cholera are not transmitted solely by drinking water. This was proven most impressively 140 years after John Snow in 1991 in Trujillo/Peru (Swerdlow et al., 1992). The public water supply system was indeed contaminated with cholera germs - not least because the water was not chlorinated - but the highest risk for the individual to be hit by the cholera disease was inadequate personal hygiene (for example dipping hands into the drinking water container) and from eating unhygienically prepared food at fiestas (Table 3).
Table 3: Univariate analysis of risk factors for Cholera among patients and controls, Trujillo, Peru (1991)
The observations made by Snow right through to Swerdlow allow the conclusion that the factor "water" and the problem of diarrhoeal diseases link up via two different mechanisms (which also require different intervention strategies): The infection can be transmitted by a direct water supply (water-borne) or the infection can be transmitted because of the lack of water for personal hygiene (water-washed).
The problem is that the water-borne and water-washed categories are not mutually exclusive, and all faecal-orally transmitted diseases can be passed on both by waterborne and water-washed means and the percentage of each type of transmission depends not only on the etiology but also epidemiological and socio-economic factors and can greatly vary from case to case. Faecal-disease-bearing germs can directly reach the host by water (waterborne) or via the hands, food, flies or from the fields (Table 4). The problem of controlling diarrhoeal diseases is one of assessing the extent to which the frequency of diarrhoeal diseases could be reduced through an improved quality of drinking water vs. greater quantities of water of unimproved quality parallel to hygiene education measures (e.g. water and soap!).
Table 4: Multiple Transmission Routes
Routes of possible transmissions of disease from faeces. PB, primary barrier; SB, secondary barrier. Source: Transactions of the Royal Society of Tropical Medicine and Hygiene, Vol 87, p S3/44, 1993. Figure: M. Sehring
Water quantity and hygiene education
An analysis of 53 intervention programs (Esrey et al., 1985) found that better quality water brought about a 16 % average reduction in the frequency of diarrhoeal diseases, whereas improving the availability of water leads to an average reduction of diarrhoeal diseases of 25 %. Even if more strict selection criteria were applied (see Table 5) the results remain the same Increasing the quantity of water has a greater influence on preventing diarrhoeal diseases than improving the quality. Hygiene measures and hygiene education which should be accompanied by a greater availability of water in conditions of poverty experienced in many developing countries, should concentrate on the following four measures (Cairn-cross, 1990):
Table 5: Median reductions in diarrhoeal disease morbidity from improvements in one or more components of water and sanitation
- washing of hands
- washing of food
- washing of cooking utensils and crockery
- disposal of children's stools.
In an outbreak of bacterial dysentery, a 69 % reduction in secondary infection was possible thanks solely to a massive effort to promote washing hands with soap (Khan, 1982).Thesamemeasure, but not using soap, in a control group led to a far lower reduction in the incidence of diarrhoeal diseases. To control diarrhoeal diseases, two basic strategies can be taken:
· Reduction of diarrhoea-induced mortality by improved case management, particularly oral rehydration therapy (ORT), promotion of breast-feeding, antibiotics (in strictly indicated cases, particularly in cases of bloody diarrhoea) and specific care of disease episodes for people suffering from malnutrition and undernutrition. Efforts to promote the care-seeking behaviour and improved access to primary health care services are also of substantial importance if mortality rates are to be reduced.
· Reduction of diarrhoea-induced morbidity by improving the quality and quantity of water, the sanitation conditions, promoting health and hygiene conditions, empowerment of women and, finally, promoting family planning, because fewer children, born at greater intervals suffer from far less episodes of disease and diarrhoea.
1. To control diarrhoeal diseases a sufficient quantity of water is often far more important (or at least equally important) as improved quality of water. Where diarrhoea is endemic and overall faecal contamination is high, it is reasonable to focus on quantity rather than quality of water.
2. The significance of water and wastewater measures to control diarrhoeal diseases differs greatly from region to region and in line with the corresponding etiology and epidemiologic situation.
3. Hygiene behaviour is often a decisive determinant for achieving a sustained Improvement in the control of diarrhoeal diseases and should receive far more intensive pro motion (health and hygiene education in the scope of primary health care).
4. The established programmes to control diarrhoeal diseases operated both by the WHO (Division of Control of Diarrhoeal Diseases) and also by the GTZ in the framework of district health projects still focus too exclusively on case management particularly using oral rehydration. It is however acknowledged that these measures were of paramount importance in reducing the global diarrhoeal-specific mortality over the last decade.
Bern C. et al.: The magnitude of the global problem of diarrhoeal disease: a ten-year update. Bulletin of the World Health Organization, 70 (6): 705-714 (1992)
Cairncross, A.M.: Health impacts in developing countries: new evidence and new prospects. Journal of the Institution of Water and Environmental Management, 4,571-577
Esrey, S.A. et al.: Intervention for the control of diarrhoeal diseases among young children; Improving water supplies and excreta disposal facilities: Bulletin of the World Health Organization, 63,757-772 (1985)
Hennekens, Charles H.: Epidemiology in medicine, p. 5-8 (1987)
Kawata, K.: Water and other environmental interventions the minimum investment concept. American Journal of Clinical Nutrition, 31, 2114-2123 (1978)
Khan, M.U.: Interruption of shigellosis by hand washing. Transactions of the Royal Society of Tropical Medicine and Hygiene, 76,164-168 (1982)
Kolsky, P.J.: Diarrhoeal disease: current concepts and future challenges: Water, sanitation and diarrhoea: the limits of understanding. Transactions of the Royal Society of Tropical Medicine and Hygiene (1993) 87 Supplement 3,43-46
Swerdlow, David S. et al.: Waterborne transmission of epidemic cholera in Trujillo, Peru: lessons for a continent at risk; The Lancet, Vol 340: 28-33 (1992)
Pour prnir les des de maladies diarrhues comme le chol, de nombreux programmes de dloppement rise jour ont exerceur effort en direction d'une amoration de la qualite l'eau. Des des scientifiques auxquelles l'auteur fait rrence montrent toutefois que l'accroissement des disponibiliten eau,liescampagnes d'cation en mati d'hygi, semble reprnter une strate plus porteuse. L'auteur est d'avis que les programmes de santevraient e modifin consence.
Hasta la fecha, uno de los instrumentos mas importantes que han utilizado los programas de desarrollo para prevenir epidemias de enfermedades diarreicas tales como el colera ha sido mejorar la calidad del agua potable. Sin embargo, los analisis cientcos presentados por el autor indican que podria ser mas efectivo aumentar la oferta de agua y realizar simultanemente programas de educacion higico-sanitaria. Seg autor, convendradaptar los programas de salud a estos nuevos conocimientos.