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Wednesday, 21 November 2012

Disease and sanitation

Action in low-income communities 
by Professor John Pickford of the Water, Engineering and Development Centre at Loughborough University of Technology.
It is often said that much of the disease in low-income countries is caused by bad water. Water-related diseases, so we are told, cause the deaths of many millions of children each year and occupy most of the hospital beds in developing countries. Diarrhoea in its various forms is a killer, as well as causing pain and suffering.
Water quality is unfairly blamed for all these problems. However, nearly all so-called water-carried diseases, from quick-killing cholera to uncomfortable stomach-ache, are really spread through poor hygiene and sanitation practices. Lack of sanitation may mean that water is contaminated but these diseases are also passed on in other ways. The diagram on page 2 shows some of the other ways in which diseases can be spread from the faeces of the infected person to other people.
The spread of disease
In Tanzania a medical officer told me about his investigations into the quite serious cholera outbreak in the mid-1970s. He had tried to work out how the infection spread. In one rural area a map marked with cholera cases showed clearly that all were along a stream used as water supply. Once the stream was polluted by cholera bacteria, people downstream were likely to be infected. But in Dar es Salaam (the capital city) he could find no connection between the epidemic and water. Here it seemed many women had contracted the disease while tending sick relatives and carrying out rites on those who had died. Their hands acted as the carrier.
Washing hands
In this example, as in many others, a lack of water for washing helped the spread of disease. Thorough washing of hands is so important in preventing the spread of infection. Washing with soap or ashes is best, but the essential thing for good health is to have enough water. Water for washing does not have to be of the same quality as drinking water.
Flies are also responsible for much of the spread of disease. Cockroaches are sometimes to blame too, but flies are the real villains. The trouble is that they like feeding on faeces. They can also travel long distances. Flies have spikes on their legs, so particles of whatever they feed on are carried away. If their food is faeces of someone suffering from a diarrhoea-type disease such as cholera (rare) or gastroenteritis (common), these particles may pass on the disease to others. Their next meal is quite likely to be on human food. So bits of faeces are left behind on food or drink which is to be eaten by people. The disease is passed on.
Disease spread through soil
Another route is in soil. This is very important for intestinal worms such as roundworms and hookworms. Children with roundworms often relieve themselves while crawling or playing in an unpaved compound. The faeces are likely to contain roundworm eggs. Even if someone cleans the compound, some eggs probably remain in the ground. Other children get some soil on their hands – children everywhere get dirty when playing. Then fingers go in mouths because children everywhere suck their fingers. The roundworms are passed on. One of the problems with roundworm eggs is that they remain infective for a very long time – many months. When children (or adults) with roundworms defecate on the ground near food crops, soil containing eggs can also easily get onto the crops many months later. Roundworms can then be spread through the food.
Disease spreads very easily
When particles of faeces from someone with a so-called ‘water carried disease’ are passed on by water, hands, flies or the ground, the disease may be transmitted to someone else. A tiny amount of faeces is enough. People excrete several thousand million micro-organisms every time they defecate. Most of these organisms are harmless, but it only requires a few of the dangerous ones for fresh infection.
The value of sanitation in preventing disease
The aim of sanitation is to block all these ways of spreading disease. This diagram shows how good sanitation prevents the micro-organisms in faeces from spreading disease.
It is important to reduce hand contact with faeces. Washing hands well after contact with faeces must go together with sanitation to reduce all risk of disease transmission. Washing hands is particularly important after cleaning a baby’s bottom. It is often wrongly assumed that the faeces of young children are harmless.
The use of latrines
Where there are no latrines people have to relieve themselves in the open. They may do this at any nearby place – in fields or the bush, on the roadside, beside railway lines and canals, on any vacant land. As villages and towns grow it becomes increasingly difficult to find places to defecate in private. Privacy is usually more important for women than men. The destruction of trees and other vegetation (an environmental problem in many parts of the world) adds to these difficulties. No trees or bushes may mean no natural screen to give privacy.
Most people want to keep the immediate surroundings of their homes clean, so it is necessary to go some distance from home to defecate. In some circumstances this may be acceptable. However, in bad weather, having to walk half a kilometre may be very inconvenient. It may be difficult or impossible for the old or infirm, or for young children whose faeces are often particularly dangerous. A long walk is especially difficult for anyone suffering from severe diarrhoea.
Until the 1960s a common method of dealing with excreta in many Third World towns was the dry latrine or bucket latrine. If well run, the system was reasonably satisfactory for the user. Users defecated into a bucket or other container that was regularly emptied. Emptying was often carried out at night; hence the name ‘nightsoil’. There are still many such latrines, although they are a serious health problem. The system involves handling of fresh excreta and there is much nuisance from smell and flies. Excreta is spilled near the latrine and along the routes used by the nightsoil men.
Advantages of pit latrines
Wealthy urban areas may have WCs, sewerage and proper sewage treatment with piped water supplies. However, for the majority of people in both urban and rural areas, this is out of the question.
For most people the best sanitation solution is some form of pit latrine. The pit is simply a hole in the ground to hold faeces. There is no pollution of above-ground water or the soil and disease is not transmitted through these routes. There is no need for fresh excreta to be handled.
Faeces decompose and are converted to gases and liquid, leaving solid remains. The gases escape to atmosphere or into the soil. If the surrounding soil is suitable is soaks up liquid from decomposition, plus urine, water from cleaning the latrine and a small amount of other waste water put into the latrine.
The solids that remain gradually fill latrine pits. A pit may last for a long time if it is large and ground conditions are favourable. I have examined many pit latrines in East Africa that have been used by large families for more than twenty years, have never been emptied and seemed to have plenty of space left for future use.
There needs to be some support over the pit for users to squat or sit. This ‘slab’ needs to be strong enough to support the user’s weight. If it has a rough surface (as when made of unplaned wood or mud) it may provide a suitable residence for hookworms. A smooth concrete slab is ideal – it is strong and easy to clean.
More about flies
Fly-breeding in pits is a health hazard already described. This is not a great problem with a very deep pit with a small squat hole. But flies can be a serious problem with a shallow open pit or nearby full deep pit. There are three ways of controlling this fly nuisance.
The cheapest is to make a lid that fits exactly in the squat hole and to make sure it is always replaced when the latrine is not actually being used. In Mozambique a low-cost, slightly domed, unreinforced concrete slab is popular. The squat hole is keyhole-shaped. In the keyhole a lid is cast, made of concrete with a wood handle. This type of latrine can be made with a cheap shelter for privacy – grass matting is sufficient.
In Zimbabwe thousands of ‘Ventilated Improved Pit’ latrines (VIPs) have been built. VIPs require a latrine building with roof and cost much more than the Mozambique-type latrine. The pit is ventilated by a pipe or chimney with fly-proof netting at the top. Hundreds of flies may hatch in the pit from eggs laid by one or two mother flies that manage to get in. They are attracted by light at the top of the vent, while the latrine building is darker. Unable to get through the netting, they die.
The third method of controlling the fly nuisance can be used where people use water instead of paper or leaves for cleaning themselves after defecation. A trap with a water seal is fitted below a shallow pan. The trap is like that in a WC but not so deep. It is flushed by pouring a small quantity of water. Flies, mosquitoes and smells in the pit are all effectively trapped by the seal, with obvious reduction of health risks.
A final point to be considered is what happens when a pit becomes full. In rural areas a new pit can be dug but this may be impossible on small urban plots. Emptying a recently filled pit with buckets exposes the workers to health risks. A few fortunate towns have special vacuum tankers for emptying pits. An idea which has been found helpful in many other places is to make two small pits or to divide one pit into two sections. One section or pit is used for two or three years, and then the other. By the time the second pit is full the excreta in the first pit will be quite safe to take out by hand.

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