• Kai is a contributing correspondent for Science magazine based in Berlin, Germany.

Cucumbers May Be Culprit in Massive E. coli Outbreak in Germany

26 May 2011 3:50 pm

German researchers suspect cucumbers from Spain are the source of a massive enterohemorrhagic Escherichia coli (EHEC) outbreak that has hit the northern parts of the country. According to the Robert Koch Institute (RKI), so far 214 patients have developed hemolytic-uremic syndrome (HUS), a potentially deadly complication of an EHEC infection, characterized by a destruction of red blood cells and severe kidney problems. At least two patients have died.

Local authorities in Hamburg announced today that they had isolated the EHEC bacteria from four cucumbers. Three of the samples came from a big market in Hamburg that sells to greengrocer's shops as well as restaurants and caterers. Those cucumbers came from two organic producers in Spain. Scientists had speculated in the last few days that manure from infected animals used on an organic farm might have spread the bacteria to vegetables. A fourth sample came from a restaurant, and it was not immediately clear where that cucumber had been grown. After the announcement, stores started taking Spanish cucumbers off the shelves.

Consumers had already been hesitant about vegetables since scientists at RKI and the Federal Institute for Risk Assessment announced the results of a first case-control-study on Wednesday evening: Women who had become infected with EHEC were a lot more likely to have eaten raw tomatoes, cucumbers, and lettuce in the days before falling ill than women who had not fallen ill.

The scientists used a detailed questionnaire to ask 25 female EHEC patients and 96 women living in the same areas about what they had eaten in the days before the outbreak. Only women were included in the study because they have fallen ill more often than men in the outbreak. "It also strengthened the results of the study, because it meant that we could ignore all sex-specific differences in eating habits," says Gérard Krause, head of the department for infectious diseases epidemiology at RKI.

A statistical analysis revealed that 92 % of the women who had become infected had previously eaten tomatoes. Only about 60% of healthy women had done so. "For something that people eat so frequently, this is a big difference," says RKI expert Klaus Stark. The results for cucumbers and lettuce were similar but slightly smaller. All three results were statistically significant. The experts advised Germans, particularly in the north, not to eat any raw tomatoes, cucumbers, or lettuce until further notice.

That advice remains in place. "It is certainly a possibility that more than one of these foods is responsible," says Reinhard Burger, president of RKI. Scientists also want to be sure that the results from Hamburg are confirmed in another lab.

New insight into the nature of the bacterium might help them. Scientists at the National Consulting Laboratory on Hemolytic Uremic Syndrome in Münster have samples from all 42 EHEC cases that have occurred in HUS patients in Germany since 1996. They have identified the strain in the current outbreak as HUSEC41, sequence type ST678. In the common serotype classification that means the pathogen is an E. coli O104:H4

According to Helge Karch, head of the laboratory in Münster, O104:H4 does not have a single documented outbreak to its name. "That is why we were very surprised, that this strain could cause severe illness in such a short time," he says.

Karch and others are now working on sequencing the whole genome of HUSEC41 and establishing a new and quick way of diagnosing this particular strain of EHEC. That is important because the bacterium is hard to distinguish from normal, nonpathogenic E. coli.

The strain is also eae-negative, which is unusual for a pathogenic E. coli. The gene eae encodes the protein intimin, which the bacteria uses to attach to the intestinal wall. "That has been shown to be particularly important for infecting children, so it might be one explanation, why we are seeing mainly adult patients in this outbreak," RKI expert Stark says.

Meanwhile, the outbreak is continuing in full force. "It looked for a bit, like there was a dip in the numbers, but particularly in Hamburg a lot of patients are still presenting at hospitals with bloody diarrhea," Stark said. The next few days will show whether the warning about eating cucumbers, tomatoes, and lettuce has had any impact on the outbreak.

*This item has been corrected on 3 June. A previous version of this story erroneously reported that researchers had isolated the EHEC strain O104:H4 from cucumbers.

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