The unusual E. coli serogroup O104 is suspected of being the pathogen likely to be associated with this outbreak. The epidemiological investigation into the source of the outbreak is under way. Although the source has not yet been determined, cucumbers are under suspicion, and the Robert Koch Institute in Germany is advising people, as a precautionary measure, to avoid eating tomatoes, cucumbers and lettuces, in addition to taking the usual hygiene measures in handling fruit and vegetables.