Science: Tell me about ... E. coli O157

THE revelation that many hamburgers in commercial fast-food joints might not be sufficiently cooked to kill off bacteria such as E. coli O157 is unsettling: already, this bug has acquired a lethal reputation. It was the cause of the world's worst food-poisoning outbreak, when 19 people died in 1996 in Scotland.

So is it a superbug? Not exactly. It's a strain of the common bacterium Escherichia coli - a common organism found in the gut of man and animals and in damp, mild environments such as soil and vegetation. It can also breed in moist or wet areas in factories, untreated water, and so on. There are many types and strains of E.coli, a few of which are potentially pathogenic.

Of these, E. coli O157 (the "O" is the letter, rather than the number zero) has only been identified comparatively recently. It is also known as verocytotoxin-producing E.coli, or VTEC, because of the poison - or toxin - it produces when it colonises parts of the gut.

What seems to mark it out is that the infectious dose is very low compared to other E. coli strains - perhaps fewer than 10 cells.

Infection symptoms range from mild diarrhoea to severe, bloody diarrhoea and in some cases haemolytic uraemic syndrome (HUS) and kidney failure, which can be fatal. Most commonly, it affects children under four, but the elderly are also at risk - all the Lanarkshire deaths were among elderly adults.

It usually takes a couple of weeks for the symptoms to pass completely, but perhaps longer for the actual bacteria to be excreted.

So is it new? VTEC illness was first recognised early in the 1980s and reports of outbreaks and cases are now increasing rapidly; there have been well-publicised incidents in many parts of the world. In 1993 a large outbreak in America affected 732 people: the cause was undercooked hamburgers. An outbreak of bloody diarrhoea in a refugee camp in Malawi affecting 20,000 people is thought to have been caused mainly by VTEC, though some cases were probably caused by a dysentery-like illness. In 1996, Japan suffered an outbreak, probably from contaminated meat.

Yet tests on samples stored in the Netherlands suggest that VTEC may have been causing illness there since at least 1974. So in that sense, it's not new: but we've now got better at testing for it, and so we are noticing it much more.

In addition, the arrival of international transportation, jet flights and so on means that such bugs can be transported around the world (say, by someone who picked up a "tummy bug" in one country) and spread to new areas. Having arrived, though, there's no chance it will go away in a hurry: the modern world simply offers too many people and places where it can thrive, especially if just 10 cells is all it takes to infect someone.

How can you avoid it? Simple - use high temperatures when cooking: an internal temperature of 70 Centigrade for two minutes will kill it. And do not use the same surface for cooked and uncooked items, since that can re-infect something you just sterilised. One other thing: now, wash your hands.

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