TORONTO - Researchers who conducted followup health studies of residents of Walkerton, Ont., who became sick after drinking tainted water have discovered genetic risk factors associated with post-infectious irritable bowel syndrome.
Details of the study by scientists at McGill University in Montreal and McMaster University in Hamilton will be published in the March edition of the journal Gastroenterology.
The water supply in the southwestern Ontario town was contaminated almost a decade ago with E. coli and Campylobacter jejuni, leading to the deaths of seven people and causing symptoms, including bloody diarrhea, in 2,300 area residents.
Alexandra-Chloe Villani, a research associate at McGill, says this population provided a wealth of samples to study.
"Worldwide, this is the first genetic study in the field of PI-IBS," she said Wednesday from Montreal.
"It became a unique opportunity, since we knew the environmental trigger, to study the genetic risk factors."
Of the 2,300 people who developed gastroenteritis from microbial contamination of the water supply, a longitudinal study found that more than 36 per cent developed irritable bowel syndrome, or IBS, a chronic condition characterized by abdominal discomfort and disturbed defecation.
"We were wondering how come 64 per cent didn't develop anything and 36 per cent came to develop this syndrome," said Villani.
When comparing the two groups, they found variations in three genes that increased the risk of having IBS.
"It doesn't increase your risk dramatically, but what's most important about genetic studies ... is that it's an excellent tool to create the map of all of the mechanisms - biological mechanisms - that are defective in the patients," she explained.
Dr. John Marshall, a gastroenterologist at McMaster, said it may help with an understanding of the condition in the future.
"It's important to recognize that I don't think these findings are going to change our clinical management of people," he said.
"It's not something you can use to test for the condition or at this stage to predict who's going to get the condition or recover from it."
The mutations all tilt the probability one way or the other, in favour or away from developing IBS, he said.
"So the differences for any individual gene are relatively small in absolute terms. But when you have such a large population to study, you can actually detect the difference statistically between them."
The tainted water in Walkerton caused "an awful tragedy," he noted, and researchers are extremely grateful to all the people who have given their time and samples for study.
"Without them this could never happen. It is a truly unique opportunity ... It's very rare to have such a large outbreak in a population, in a developed country where we could access them and study them relatively quickly, and where there's such a high rate of participation."