Report No DWI0289
Drinking
water meeting current standards and gastrointestinal illness: A
critique of the work of Pierre Payment, with discussion of its
relevance to the UK and suggestions for a future study
DWI0289
1994
Executive summary
- In 1991, Pierre Payment
and co-workers reported on a randomized controlled trial conducted in
Canada (the Montreal study). The paper claimed that the study had shown
one third of the episodes of gastrointestinal infection in the
population were caused by drinkingtap water, even though the water met
current microbiological standards. The Epidemiological Survey Project
Group was asked to consider critically the methodology of the study, to
re-evaluate its conclusions in the light of any weaknesses found, to
assess the relevance of the study to the situation in England and Wales
and, if appropriate, to suggest a specification for the design of any
study which could be conducted here.
- The Group found some
problems with the epidemiological design of the Montreal study,
principally that participants were not blind to whether they were
drinking tap or filtered water and thus the reporting of symptoms might
have been biased. Against that possibility, a dose response
relationship was reported between rates of gastrointestinal illnesses
and variables participants were blind to ie. quality of water in the
distribution system, levels of contamination in the filters and
quantity of tap water consumed. The study was therefore considered to
be sound enough to be taken seriously in spite of methodological
limitations.
- Other criticisms of the
study included the use of reverse osmosis filters, because of the
change in the chemical composition of the water and evidence of
contamination by bacteria. This did not undermine the validity of the
study, but raised questions about the interpretation of results. It was
noted that no stool samples were collected; this might have helped to
identify the types of organism associated with the gastrointestinal
illnesses linked to drinking tap water.
- The study was considered
relevant to England and Wales because the quality of the tap water
appeared to be similar, although the quantity conserved might be lower
in England and Wales. Very limited available data suggests the rate of
gastrointestinal infections might also be lower than in Canada.
- The Group supported the
undertakings of a similar study in England and Wales and presented an
outline design and costings for a study which would eliminate the
methodological limitations of the Montreal study.
Copies of this report may be available as an Acrobat pdf download under the 'Find Completed Research' heading on the DWI website.