How E. coli infections wreak havoc on the body, causing dangerous disease — particularly in kids

Escherichia coli, or E. coli, are a diverse group of bacteria. They typically thrive within the intestines of healthy animals. And, most of the time, they're perfectly harmless.

But in some cases, certain strains are capable of causing severe disease, by rapidly spreading through the human digestive system, wreaking havoc throughout the bloodstream, and eventually damaging the delicate kidneys — leading to gruelling gastrointestinal symptoms, kidney failure and the potential for long-term health complications or death.

That's the situation right now in Alberta, where a large E. coli outbreak linked to a shared kitchen in Calgary has sickened hundreds of daycare-aged children. There have been more than 300 lab-confirmed cases so far, and 21 patients remain in hospital. Twenty of those patients, all of them children, have a severe kidney disease known as hemolytic uremic syndrome.

So how did a common type of bacteria make this many children sick?

"Bacteria are in our environment everywhere. And it's an ongoing war," said Edmonton-based intensive care physician and kidney specialist Dr. Darren Markland.

"And so certain bacteria have evolved advantages to be able to take over more territory, which is us."

In the case of the Alberta cluster, which is already one of the largest E. coli outbreaks ever reported in Canada, the type hitting kids isn't one of the typical strains that can cause several days of diarrhea, vomiting, cramps and other unpleasant gastrointestinal issues.

Instead, it's a strain called O157.

This vicious pathogen is best known for sparking previous headline-making outbreaks, including the devastating Walkerton, Ont., tragedy in 2000. 

In that instance, manure-tainted drinking water caused more than 2,300 cases and seven deaths — and a host of other smaller outbreaks linked to contaminated foods, ranging from packaged lettuce to salami. 

The O157 strain is found in the gastrointestinal tract of ruminating animals, such as cattle, but it doesn't cause them any disease since their bodies don't have the right receptors for this bacteria to tap into, said University of Guelph microbiologist Lawrence Goodridge, the director of the Canadian Research Institute for Food Safety.

But when people eat improperly cooked meat — or any items cross-contaminated by either raw meat or animal feces — this dangerous pathogen can enter the human body, starting an often-dangerous chain reaction.

The next stop is the stomach. Usually, the high acidity within that organ means most E. coli bacteria can't survive, Goodridge said. 

In the case of O157, however, he says ingesting just 10 of these single-celled organisms is enough to make someone sick.