London (CNN) — Hopes of drawing a line under the E. coli outbreak in Europe fell Tuesday as scientists said they had yet to trace the source of the bacteria that has killed at least 22 people mainly in Germany and infected more than 2,200 people in at least 12 countries.
The admission came the day after German agriculture officials said no trace of the bacteria has been found in initial tests at a farm growing sprouts, also known as bean sprouts, which is suspected of being the source of the outbreak. The company has nevertheless halted production and is recalling its products.
What is the situation now?
Lower Saxony Agriculture Minister Gerd Lindermann, who earlier raised the likelihood of a link between the producer Gaertnerhof, in the town of Bienenbuettel, and the contamination, said a “smoking gun” might never be pinpointed.
“It’s quite possible that we’ll never find the active contaminant,” Lindermann told Bild newspaper. “But this doesn’t take away from statements warning about sprouts.”
Nicola Holden, from Scotland’s James Hutton Institute, explained to CNN Tuesday what the problems were. “It’s very difficult for the epidemiologist to find the source of the outbreak because quite a long period of time has gone by, and because of the perishable nature of the food stuffs we’re looking at.
“We’re still looking at bean sprouts, lettuce, cucumber and tomatoes. Most of that will have been discarded at this point, so it’s going to be hard to find anything that was originally contaminated. We’ve seen this in other outbreaks: it’s always hard to find the smoking gun.”
But molecular microbiologist Alan McNally, from Nottingham Trent University, said so unusual was the strain of bacteria in this case that epidemiologists should be able to find the source.
“The bacteria will still be at the farm,” McNally told CNN. “This is not the kind of strain that’s going to disappear, even though the food that contained it will have neen discarded.
“This is a hardy organism and all the tools at the disposal of epidemiologists — such as genetic fingerprinting — should help to find it.”
Why are salad vegetables at risk?
McNally said large-scale E. coli outbreaks in the U.S. and Japan in recent years had both been linked to salad vegetables.
McNally said such cases were usually linked to contamination from animal waste, either in groundwater, water used in irrigation, or in slurry spread on fields as fertilizer.
Holden added that as well as landing directly on the plants, the bacteria were also absorbed into their edible parts — the leaves and fruit — through their root systems, meaning that washing alone was not always enough to get rid of contaminants.
“The threat to human health occurs because these bacteria are not simply sitting on the surface of the plant and are particularly difficult to remove post-harvest,” she said.
What is the advice for consumers?
Although it remains unclear what the source of the outbreak, German authorities are continuing to advise consumers against eating raw tomatoes, lettuce, cucumbers and sprouts.
Health authorities say the case is a reminder of the importance of basic food hygiene practices, such as keeping surfaces and utensils clean.
“Simple precautions like hand washing and not preparing food for other people when you’re sick should prevent the spread from one person to another,” Robert Tauxe, of the U.S. Center for Disease Control told CNN.
But experts insist there is no need for widespread worry.
“This outbreak seems to be confined to northern Germany, even the cases elsewhere are linked to there, and so there’s absolutely no cause for concern,” McNally told CNN.
“It’s always a good idea to wash fruit and vegetables, but people don’t need to get paranoid about eating salad.”
He added that the outbreak may help to make people more aware of of food hygiene, and that it is not just meat products that can cause food poisoning. “The general public needs to realize that anything grown in the ground that comes into contact with bacteria is a potential risk.”
Is organic food less of a risk?
All crops are grown with water and fertilizer so eating organic produce will not guard against bacterial infections. “If they want to eat organic,” McNally said, “they must understand that that fertilizer comes straight from a farmer’s field.”
“Consumers have to understand what comes with that: the intestines of cows, sheep and pigs are rich in bacteria that can cause problems if we ingest them.”
What has been the impact of the crisis on producers?
With sales of vegetables now plunging across Europe, EU agriculture ministers were meeting in Luxembourg to discuss emergency aid to farmers.
Spanish farmers are furious that German and EU health officials made a claim — that was since withdrawn — that Spanish cucumbers were the source of the outbreak.
Spanish exporters say they’re losing $290 million a week because of the E. coli outbreak in the midst of their country’s own deep economic crisis, with 21 percent unemployment. They are now demanding compensation.
EU health commissioner John Dalli said ministers would try to ensure that future warnings have “scientific basis and proof” before they are made public.
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