From farm to the plate: Europe’s deadly E. coli outbreak

From farm to the plate: Europe’s deadly E. coli outbreak

PETER COLLIGNON

E. coli is a common germ that has traditionally caused blood stream infections and urinary tract infections. The virulent strain we’re seeing in Europe which has infected more than 1500 people and killed 17 is called E. coli 0104. While this particular strain is new, there are quite a lot of other E. coli strains that have done something similar in the past. Certain strains of E. coli contain a toxin or poison called the “Shiga toxin”. This toxin causes damage to the bowel and symptoms begin with bloody diarrhoea. They can progress to clots in the blood vessels and a break down in blood cells (this process is called “haemolytic–uremic syndrome”). This eventually results in kidney failure and can cause death. In some people, clots can occur in other parts of the body, such as the brain, leading to strokes and other very serious health problems. This outbreak in Europe is the first time we’ve seen this combination of bug with this particular toxin. But the haemolytic–uremic syndrome has been found before in hamburger meat in the US (a strain called 0157) and about ten years ago in salami from South Australia (a strain called 0111). Where could this strain have started? The ultimate source for E. coli is usually food animals. In the past it’s mainly been cows, but there’s no reason why it couldn’t originate in other animals, including people. It goes something like this: the animal has the bug in its bowel, which then gets into water or into manure and is used as fertiliser. It’s then sprayed onto vegetables – cucumbers, lettuce and tomatoes – and if those vegetables aren’t heated before they’re eaten, the bug can be ingested. There is an incubation period during which the bug multiplies in the gut, which may take a few days to a week or ten days. A key concern about this strain is that it’s quite resistant to antibiotics. It’s what we call an Extended Spectrum Beta Lactamase or ESBL. That means it is likely to come from an animal – presumably a food animal – that has been exposed to antibiotics, often unnecessarily. But we can’t be definite about the source. Scientists are trying to map the genome of the new strain – what will this enable them to do? It will be helpful but it won’t solve the problem. We know this E. coli comes from animals and we know it shares many genetic traits to other E. colis. The one advantage of the mapping is we might be able to track where it came from. But that’s going to be a medium to long-term issue. In the short-term we need to identify (using culture and molecular techniques) what foods are contaminated with this bug and, if they are vegetables, then we’ve got to go further and identify what animals it originated from. There have been a large number of deaths and large numbers of people who are very sick. People in Germany have ingested this bug and travelled back to Sweden and the US and England, so there’s a potential for it to spread. If we don’t track down the intermediate and original source, then it may come back later and cause more contamination. What role does the use and overuse of antibiotics play in this situation? This is another example of antibiotics use in animals contributing to the development of more resistant strains of E. coli. Overuse of antibiotics has the perverse effect of increasing E. coli’s ability to pick up these other toxins (such as the Shiga toxin) and add to its virulence. We need to be very careful about the antibiotics we give animals. We’ve also got to be very careful what we do with the run-off from the farms with animals (or the manure or the water) because that’s going to contain these antibiotic resistant bacteria and/or other bacteria that contain toxins like the Shiga toxin. Why are women more affected by this strain of E. coli? The short answer is that we sometimes don’t know why these differences occur. Often males are more affected by things like Golden Staph and females are more affected by E. coli because they’re more likely to get urinary tract infections. Because it’s likely this strain of E. coli is coming in through food, it may be because women eat different foods to men. They’re more likely to eat healthier foods, such as fresh fruits and salads. If these haven’t been cooked, it’s more likely they will still contain this bug. But the bottom line is we don’t know yet. They haven’t identified what food source is responsible here and where it has come from. We’re a little over a month into this outbreak, what do you expect to see over the coming days and weeks? The worry is that we’re still seeing new infections and we haven’t identified the food source, so it might still be circulating. So it will be fairly telling over the next week or so if there are the same numbers or increasing numbers of people getting this infection – it would imply that we haven’t removed the food source, or water source, that’s contaminated. E. coli can spread through water? You wouldn’t expect the water supply in Germany to be contaminated. The presumption is that it’s a food. The authorities have done case-controlled studies and it’s more likely to occur in people who have had lettuce, tomato or cucumber. But in other areas of the world, antibiotic-resistant E. colis are found in water supplies, such as in Deli. The most likely scenario is that this bug got to a lettuce or cucumber, or another type of food, via water that was contaminated by an animal source. So water is probably a vehicle in this, somewhere along the chain. What lessons can we learn from this outbreak? This whole situation shows that we need to be very careful where we source food from and ensure that appropriate procedures are taken. We can’t allow superbugs, or bugs with toxins, to spread.