Jun 212011
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THE bean sprouts contaminated with a particularly nasty strain of Escherichia coli, a bug that normally lives quietly in the gut of humans and other animals, have now sickened over 3,250 people in Germany and caused 37 deaths. Since the outbreak began in May, a quarter of those infected have developed haemolytic uraemic syndrome (HUS)—a potentially fatal complication that affects the blood, kidneys and nervous system.

The genetic sequence of the bacterium in question (a wholly new version of a strain of E.coli called O104:H4) has been found by scientists in Germany and China to contain at least eight genes that make it resistant to the majority of antibiotics. Many of the patients with HUS will need kidney transplants or require dialysis for the rest of their lives.

The source of the tainted bean sprouts has been traced to an organic farm in northern Germany. The owner claims not to have used cattle manure, nor any of the three dozen or so non-organic additives widely employed in organic farming. Apparently, the only ingredients were seeds and water. The usual procedure for sprouting is to steam the selected seeds in drums at a temperature of 38ºC. Such conditions are ripe for breeding bacteria.

The question is how the O104:H4 got there in the first place? The usual route is via animal faeces that have contaminated the water used for sprouting, or from manure used directly as organic fertiliser. But both have been ruled out. By all accounts, the farm also complied with the industry’s highest standards of personal hygiene. The conclusion is that the seeds themselves must have been contaminated beforehand.

Microbiologists have long known that E.coli can bind tightly to the surface of seeds and even penetrate them, and then lie dormant for months. On germination, the population of bacteria can expand 100,000 times or more. Apart from contaminating the seeds, the bacteria get inside the stem tubers as the seeds begin to sprout. No amount of washing can then eradicate the bugs completely.

The outbreak in Germany is just the latest in a long string of food scares associated with E.coli. In 1996, a sequence of outbreaks linked to contaminated radish sprouts in Japan sickened some 12,000 people and caused a dozen or so deaths. Like the current incidence in Germany, the Japanese outbreaks (of a more common strain known as O157:H7) also caused bloody diarrhoea and HUS. The good news is that such food-borne infections are on the wane—at least in the United States. Thanks to better reporting methods, stepped up inspections and improved hygiene measures generally, the number of dangerous O157:H7 infections has been halved since the mid-1990s.

Unfortunately, that is not the case with Salmonella. According to the Centres for Disease Control and Prevention (CDC) in Atlanta, the number of confirmed cases of Salmonella infection—especially from raw meat, eggs and vegetables—increased by 10% in 2010. Memories are still strong of last year’s scare when 500m tainted eggs had to be withdrawn from the American market after 2,000 people became infected, though mercifully no-one died.

All told, the CDC reckons that one in six Americans is infected annually by food- or water-borne diseases such as Salmonella, E.coli, Campylobacter and noroviruses. Some 130,000 wind up in hospital each year, and about 3,000 die as a result of complications. In statistical terms, a fatality rate of 0.001% would seem a monumental achievement for public health. But the point is that those 3,000 annual deaths from food poisoning could easily be avoided, and millions of people spared the incapacitating symptoms of food poisoning.

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