People who fall seriously ill from E. coli poisoning are at sharply higher risk for permanent kidney disease, a landmark seven-year study of victims of Canada's tainted-water tragedy has concluded.

But the study of thousands of people in Walkerton, Ont., which was devastated in May 2000 by an E. coli outbreak due to contaminated tap water, has found no relation between E. Coli and diabetes.

"Patients who had confirmed severe gastro-enteritis had a 30 per cent increased risk of high blood pressure or kidney damage," Dr. Bill Clark, who led the internationally groundbreaking study, said in an interview.

"That will persist."

However, the study also found that treatment for the "silent complications" of E. coli poisoning prevents further progression of the damage and prevents long-term complications.

"We've been able to show that, so that's been great," Clark said.

About 22 children who were severely ill in 2000 have permanent kidney damage, but treatment has stopped the illness from getting worse. In one girl, kidney function has improved.

The outbreak in the midwestern Ontario town of Walkerton due to E. coli 0157:H7 killed seven people and made 2,500 others ill.

Some will be forever changed

It was one of the worst public health disasters in Canadian history and led to sweeping changes in the laws and practices related to municipal drinking water.

"The reality is that there are some people who will be forever changed by this epidemic and tragedy," Clark said.

Clark, who was in Walkerton on Thursday to provide his final report on the health study to the town, said the results should help improve outcomes for "a lot of communities" hit by E. coli outbreaks around the world.

Coincidentally, his report came as health authorities in North Bay, Ont., were investigating 93 possible cases of E. coli poisoning linked to a fast-food restaurant.

It's clear from the Walkerton study that those who fall ill should have annual followup assessments for at least a couple of years for kidney and blood pressure problems, Clark said.

One unexpected finding was the discovery that about five per cent of people in Walkerton were drinking "excessive" amounts of water — more than three litres a day — and possibly damaging their kidneys in the process.

Less water slows kidney aging

Clark said the problem — which runs counter to popular wisdom that drinking lots of fluids is healthy — appears to be reflective of the population at large.

"We may be stopping a new epidemic of kidney aging, which could result in a lot more dialysis 30 to 40 years from now," Clark said.

Poison from the hardy E. coli 0157:H7 bacterium damages small blood vessels, including those in the lining of the intestines, resulting in characteristic bloody diarrhea.

The very young and frail elderly are especially susceptible to kidney failure or even strokes resulting from infection.

The study also found the incidence of irritable bowel syndrome — which can cause severe abdominal pain and bouts of diarrhea or constipation — was about twice that of the normal population.

However, that declined over time, with about 80 per cent of those affected getting better.

Even more positively, Clark said, 88 per cent of people in Walkerton now rate their own health as good to excellent, an exceptionally good result.

The study began with more than 4,500 people, with about 2,800 remaining through the full seven years.

Clark was full of praise for the community's involvement.

"We came at a very difficult time for the people in Walkerton," he said.

"They had just gotten through a very difficult process and then we launched into an intrusive and invasive study, but they participated and made it all possible."