Could the problem be due to imported food?
We are used to bacteria which we meet around us every day, but may not have been into contact with imported bacteria before and hence have not built up immunity to them.
A bacterial cell such as E.coli can multiply within 20 minutes in ideal growing conditions - the gut is the perfect place (37oC and nutrients) and some bacteria can also readily exchange DNA with other types of bacteria or phages (these are like viruses that infect bacteria) - so new strains of bacteria (eg different types of E.coli) can emerge readily with a rapid growth in cell numbers. This is a natural course of "evolution" and nothing sinister about it. It is one of the reasons why bacteria are one of the most studied forms of life because of the genetic diversity and rapid growth and scientists can use them to learn about genomes and make medicines.
The immune response is a bit more complicated - because there are so many types and strains of E.coli, we don't all have the same antibody response, even a population within the same country. It would be nice to think the outbreak was the result of imported food but there are many sources of contamination.
In this case, the E.coli strain was found in highest numbers from a different animal species (bovine) so the most likely source of contamination is from vegetables grown in cow manure and poor hygiene to wash the food and hands after handling.
Severe illness (or even death) is not down to the bacteria itself but the toxins (natural by products) they produce and this can cause serious diarrhoea and dehydration as the body tries to get rid of it from the body as quickly as possible. This can also lead to kidney failure in extreme cases as fluids are pumped from the blood system into the gut to facilitate rapid expulsion to get rid of the source of infection. The effect of the toxin (rather than the bacteria) is the cause of haemolytic uraemic syndrome (the red blood cells are haemolysed/break down)
With regards to using raw manure versus rotted down, although it is likely most of the bacteria will have died, some will remain viable but just be dormant. The soil is teaming with microbes most of which are naturally occurring but if food is improperly prepared, these can become pathogens. A classic case is the Clostridium botulinum which is found in soil but only becomes deadly if preserved food is done incorrectly.
I hope I wasn't too technical
but I just wanted to dispel any myths. I think the title of this thread should be "now wash your food and hands" to remind people to go back to basics