Trachoma and water
Trachoma prevalence and transmission
There are four reasons why one might expect improvements in water supply to reduce the transmission of trachoma in a community.
- Children’s faces are the sources and sites of re-infection with the organism, Chlamydia Trachomatis, which causes the disease. Increased water availability means that faces can be cleaned more thoroughly and more frequently.
- It also means that the objects which carry the organism between one person and another (such as fingers and bedclothes) can be kept cleaner and are less likely to be infected.
- Trachoma is transmitted by flies (see the article in this Issue). If there is more water in a dry environment, including water spilt or thrown on the ground, this will provide alternative sources of moisture to flies which would otherwise seek it on children’s faces.
- Finally, the water supply helps people to maintain a cleaner domestic environment (for instance, by washing dishes rather than leaving them around with food remains on them). The environment will be less attractive to flies.
Trachoma and water supplies
Certainly, trachoma is generally found in the more dry parts of the world, such as the Sahel, India, and the Australian interior where water is scarce. However, the relationship between water supplies and trachoma is sometimes more complex than it might seem, and the proof that water supply improvement can help to reduce trachoma can sometimes be difficult. One study from Ethiopia1 even found that people living further than 15 minutes’ walk from a water source had less active trachoma than those with a source of water closer at hand.
Part of the explanation for such negative study results is that hygiene improvements do not follow automatically from the provision of a convenient water tap. If we study overall domestic water consumption as an indicator of hygiene and the time required to collect a bucket of water as an indicator of water availability, we find that the relationship between them takes a rather surprising form (Fig. 1).
The surprising part is where the water source is less than half an hour’s round trip away from the household. In general terms, a half hour round-trip water collection journey corresponds to a distance each way of about 1 km (walking at 4 km/h, with no queue at the tap). When the existing source is farther away than this, then a tap closer to the home can be expected to lead to an increase in consumption. However, when this level of availability has already been reached, bringing the water source closer to the door has practically no influence on water consumption, unless the water is provided in the yard or in the house.
This ‘water use plateau’ has been documented by studies in East, West and Southern Africa, Asia and Central America. It means, that for people who are already on the plateau, a water supply providing an in-house level of service will increase their water consumption, affect their hygiene and by implication reduce their level of trachoma. If house connections of water are not feasible or affordable, priority in allocating water supplies should go to those who are farthest from their water source, and farthest off the ‘edge’ of the plateau. That priority will help to ensure the maximum benefit in terms of eye health. Happily, it will also give the maximum benefit in terms of diarrhoeal disease reduction and also save in the weary task of carrying water. Water supplies which are good for health in general are also best for trachoma control.
In fact, both water and sanitation are good for trachoma control. A number of studies1, 2 have found less trachoma in families with latrines. Latrines help to control the Musca sorbens flies which land on children’s faces, which may explain why they protect against trachoma.
The total amount of water people use gives only a crude indication of their hygiene. How the water is used determines whether it will help to control trachoma. For example, a study in The Gambia3 found that the total quantity of water used by a household had no effect on the prevalence of active trachoma, but that trachoma-free households used more water for washing children than households with trachoma cases.
Trachoma and health education
This raises the possibility of using health education to encourage the use of water for specific hygiene purposes such as face-washing. Health education is probably cheaper than building water supplies; even so, there are no specific resources in most poor countries for health education simply to prevent trachoma. On the other hand, adding too many messages to an existing health education programme weakens its impact, so that health educators may be unwilling to add a trachoma message to an already overburdened programme.
One promising possibility is that hand-washing, which is increasingly promoted to prevent diarrhoeal diseases, may also help to prevent transmission of trachoma and other eye infections. Fingers have been considered an important means of transmission of trachoma for sixty years,4 and a field study from Indonesia3 has shown that an intervention to promote hand-washing could be successful in reducing not only diarrhoea but also eye infections. As with the water supply itself, this is an example of how good primary health care can help to prevent trachoma best when it also prevents other diseases.
1 Zerihun N. Trachoma in Jimma zone, Southwestern Ethiopia. Tropical Medicine and International Health 1997; 2: 1115-21.
2 Courtright P, Sheppard J, Lane S et al. Latrine ownership as a protective factor in inflammatory trachoma in Egypt. Br J Ophthalmol 1991; 75: 322-5.
3 Bailey R et al. Trachoma and water use; a case control study in a Gambian village. Trans Roy Soc Trop Med Hyg 1991; 85: 824-8.
4 MacCallan AF. Epidemiology of trachoma. Br J Ophthalmol 1931; 15: 361-411.
5 Wilson JM et al. Hand-washing reduces diarrhoea episodes: a study in Lombok, Indonesia. Trans Roy Soc Trop Med Hyg 1991; 85: 819-21