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Friday, June 17, 2011
Food poisoning: The Difference Engine: Gut feeling
The Difference Engine: Gut feeling The Economist Jun 17th 2011, 17:00 by N.V. | LOS ANGELES
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 ofE.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 withE.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 ofSalmonella 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.
It is practically impossible to prevent at least some bugs getting into food in the field, no matter how stringent the hygiene rules. And washing fresh produce removes little more than surface dirt. The only answer is irradiation. That means treating food with high-energy bursts of electrons or photons to attack the micro-organisms' DNA, preventing them from spitting out dangerous toxins and proliferating.
The food industry welcomes the idea. Irradiation destroys 99.9% of common pathogens, reduces the need for chemical pesticides and fumigants, extends shelf life by slowing down the ripening process, and eliminates the need to quarantine fruit and vegetables from abroad. Irradiation is used widely in France for ensuring the safety of deboned poultry meat. Frozen seafood and frogs legs are similarly treated in Belgium, France and the Netherlands. Elsewhere, irradiation is employed extensively to eradicate bacteria and moulds in spices, dried vegetables and seasonings. In America, irradiation has long been approved for killing the pathogens in meat, and (following the E.coli scare in 2006) for treating spinach and lettuce.
The World Health Organisation, the American Medical Association and the American Dietetic Association, among others, are strongly in favour of food irradiation. Many medical researchers and food scientists would like to see irradiation become the fourth pillar of public health, taking its place alongside chlorination, vaccination and pasteurisation. They see the benefits as far outweighing any risks the technology may entail—especially as it is now done, not by bombarding food with radiation from X-ray machines or radionuclides such as cobalt-60, but with a beam of electrons from an emitter similar to the kind found in traditional television sets.
But despite its private enthusiasm for irradiation, the food industry is leery of embracing the technology in public. In America, the Food and Drug Administration requires that irradiated-food packages carry the international "Radura" symbol (coined to symbolise "irradiation" and "durability") along with the words "Treated with/by irradiation". Few supermarkets have been willing to stock such products, fearing customers will mistakenly associate the wording with nuclear fallout.
Advocacy groups such as the Centre for Food Safety, the Food and Water Watch and the Organic Consumers Association have opposed food irradiation, not on grounds that the technology is risky, but because it does not address the root cause of outbreaks—namely, the unsanitary conditions found on many farms and in food processing plants. Such concerns are genuine. Unfortunately, though the authorities have stepped up inspections to improve hygiene, there is no way that the food industry, no matter how scrupulous, can be made bug-free using disinfectants and washing alone. Only additional processing with irradiation can ensure that.
In his weekly column in the Wall Street Journal, Matt Ridley, a former science editor ofThe Economist, noted that Germany is a classic example of what is known as the "precautionary principle"—the notion that the burden of proof is on the innovator to demonstrate that a new technology is safe before it can be approved. The precautionary principle holds all new technologies to far higher standards than existing ones.
In Europe, for instance, genetically modified foods must be labelled so that they can be traced "from farm to fork". Yet, organic crops fertilised with animal manure have no such requirements—even though they pose a far higher risk to human health. Under United States Department of Agriculture rules, excrement used as an organic fertiliser must be composted to a sterilising temperature of over 70ºC, and the treated crop then kept for 120 days before being harvested. Given the exigencies of the business, that rarely happens.
By the same token, America requires that irradiation of food be shown to be not just beneficial, but to do no harm whatsoever. According to Michael Osterholm, director of the Centre for Infectious Disease Research and Policy at the University of Minnesota, that is a standard to which even medical products such as hip joints and vaccines cannot hope to aspire.
The irony, as Mr Ridley points out, is that when, in 2000, the European Commission proposed that irradiation be allowed for a greater range of foods and at higher doses, it was the German government (fearful of the country's vociferous green movement) that vetoed the idea. Harvested bean sprouts would seem a perfect candidate for such treatment. Having now witnessed the tragic consequences of allowing a dangerous pathogen like O104:H4 to get loose in the country's food supply, one can only hope that Germany will now lead the world in embracing the merits of irradiating food. Along with presumably countless other consumers, your correspondent would heartily welcome such a move.