Shiga toxin-producing E. coli (STEC) O104:H4 2011 outbreaks in Europe: Taking Stock

On 21 May 2011, Germany reported an ongoing outbreak of Shiga-toxin producing Escherichia coli (STEC), serotype O104:H4. From an initial case control study, the outbreak was associated with the consumption of fresh salad vegetables. Subsequent investigations showed that the risk of infection was significantly associated with the consumption of fresh sprouted seeds rather than with other fresh vegetables. A tracing back and tracing forward study showed that all of the clusters for which there was sufficient information, could be attributed to consumption of sprouted seeds from a single sprouted seed producer in Germany. Investigation of the production site showed no evidence of environmental contamination. Employees were found to be infected, but since they had not become ill prior to the outbreak, it was concluded that they were not the source of the food contamination. Hence, contaminated seeds used for the sprout production were the most likely source. Several varieties of seeds were used, and sprouts thereof were sold as a mixture. Subsequently, a cluster of patients with bloody diarrhoea was reported, after having participated in a local event in France on 8 June. Consumption of sprouted seeds was also associated with occurrence of the disease in this cluster. Furthermore, the STEC isolates responsible for the outbreaks in France and Germany were found to be indistinguishable. It was therefore concluded that there was a common source for both outbreaks. A comparison of the back tracing information on the seeds from the French and German outbreaks led to the conclusion that a specific consignment (lot) of fenugreek seeds imported from Egypt was the most likely link between the outbreaks, although it could not be excluded that other lots from the same exporter and importer were also implicated. STEC O104 is a very rare serogroup in humans in the EU and worldwide. Sporadic cases in the EU have been previously linked to travel to North Africa, the Middle East and Central Asia. On 26 July, the Robert Koch Institute declared the outbreak finished. A total of 3911 cases have been reported to the ECDC and WHO, linked to the outbreaks, to date.