The outbreak is unusual in that it has developed very rapidly, and an unusually high number of cases affect adults (86% are in people aged 18 years or older), particularly women (67%), instead of the normal high-risk groups, which are young children and the elderly. Nevertheless, cases have also been reported in school-aged children. 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.