The Legendary Walkerton, Ontario HUS Outbreak of 2000

In a recent Kidney International Supplement issue dealing entirely with TTP/HUS, there are two interesting articles regarding the Walkerton, Ontario HUS Outbreak: the largest public health disaster involving municipal water in Canadian history.

In May 2000, approximately 2300 residents (out of about 5000) of this rural farming town came down with a diarrheal illness caused by E. coli O157:H7. Essentially, a breakdown in public health checkpoints led to contamination of the water supply with the bacteria (shed by 20% of the cattle raised in the area) after a period of heavy flooding.

Not surprisingly, a significant number of cases of childhood HUS was reported: a total of 24 cases. One of the articles in this issue reports on the outcome of 22 of these 24 patients.

Patients with HUS were identified based on the development of anemia, hemolysis on blood smeark, a platelet count <> 95% for age and gender, and/or the appearance of hematuria or proteinuria. The mean age was about 5 but had a wide range. Eight of the children required dialysis, all of which was administered as peritoneal dialysis. There was one child who unfortunately died; of the survivors all fortunately were able to come off of dialysis eventually and a 1-year follow-up showed a GFR > 90cc/min per 1.73 m² in all but 2 patients.

The outbreak is interesting at a number of levels, including giving a large enough sample size to estimate the risk of developing HUS as a result of E.col O157:H7 exposure--only 24 of 564 children with diarrhea went on to develop HUS, leading to an estimate of about a 4% risk. This estimate is lower than previously suggested rates.

I wonder if there are any genetic differences to explain why certain children develop HUS in response to infection whereas others do not? This would certainly seem like a suitable and large enough sample size to begin asking these types of questions.