|Oral Rehydration Therapy and the Control of Diarrheal Diseases (Peace Corps, 1985, 566 pages)|
|Module Two: Diarrhea, dehydration and rehydration|
|Session 5 - Rehydration therapy|
Many of you have asked about the use of dirty water in making up oral rehydration solution when clean water is unavailable. Richard Feachem suggests that the benefits of early replacement of water and electrolytes in acute diarrhoea far outweigh the possible risk of using contaminated water.
Mothers are encouraged so prepare oral rehydration fluid using only clean water. However, most people in rural areas of developing countries have no access to clean water and in some communities the only available water is heavily contaminated with faecal material(1). In these circumstances it is recommended that the water be boiled and allowed to cool before preparing the oral rehydration fluid. This is often impracticable - involving use of expensive fuel and delaying the start of treatment. If oral rehydration therapy becomes common place in villages it is certain that the ore's rehydration fluid will often be made up with water containing pathogens of faecal origin. Does this matter? The answer is we don't yet know but it probably doesn't.
The main questions
The dirty water used to make up the fluid may contain faecal viruses, bacteria and intestinal parasites. Of these only tile bacteria may multiply if conditions are right. Oral rehydration fluid is normally used for about 24 hours after it is prepared and therefore the two central questions are:
· can certain bacterial pathogens that may be present in water multiply in oral rehydration fluid stored in the home at 20-30°C
· if they can, what is the effect of ingesting a large dose of bacterial pathogens on an intestine already colonized by the same pathogen or by another viral, bacterial or protozoal pathogen
Only multiplication (rather than enhanced survival) of a pathogenic bacterium in oral rehydration fluid is important, since only if multiplication takes place might the child receive a greater dose of the bacterium in the oral rehydration fluid than in plain water.
The results of laboratory experiments are conflicting. Some have found a steady decline in the numbers of pathogens introduced into oral rehydration fluid. On the basis of these findings a WHO Scientific Working Group(2), concluded that "Escherichia coli, Vibrio cholerae, Salmonella and Shigella do not multiply in oral rehydration fluid and survive in declining numbers for up to 48 hours".
This is unlikely to be true in all circumstances and one recent study has shown that V. cholerae and entero-pathogenic and enterotoxigenic strains of E. coli increased in concentration by between 1 and 5 log10 units after 24 hours in oral rehydration fluid. However, all these experiments used oral rehydration fluid made up with distilled water, or with sterilized surface water and therefore failed to duplicate actual field conditions.
A more relevant study on the behaviour of wilds E. cold in oral rehydration fluid made up with well water has recently been reported from The Gambia.(3)
The concentration of E. cold in well water alone fell slightly during 24 hours storage (2330° C). However, in well water plus oral rehydration salts the concentration increased by over 2 log10 units. The same study compared the response of children (three months to four years) receiving oral rehydration fluid made up with well water with those whose fluid was made up with sterile water. There was no difference in the incidence and duration of acute diarrhoeal attacks, or in the growth rates, between the two groups it was estimated that the E. cold ingested in stored oral rehydration fluid were at most 5 per cent of the E. cold regularly ingested in food eaten by these children in The Gambia.
A sound strategy
In conclusion, some bacteria may multiply in stored oral rehydration fluid. There is no evidence, however, that using contaminated fluid increases the incidence severity or duration of diarrhoea, and there is one study indicating that it does not.
A sound strategy, pending more field research, is to advise mothers to use the cleanest water available, to boil it where possible and not to keep the oral rehydration fluid more than 24 hours. To those who express concern at this approach it must be stressed that the proven benefits of water and electrolyte replacement early in acute diarrhoea far outweigh the possible risk of using contaminated water.
(1) The Lancet, August 2 1980 pp 255-256
(2) Report WHO/DDC/79.3
(3) Transactions of the Royal Society of Tropical Medicine and Htgyene, 1980, Vol. 74, pp 657-662.