The increase of serious EHEC diseases in the northwest Lower Saxony in summer 1997 was accompanied by a lively discussion on the hazard represented by this pathogen which gained a large amount of media attention. The Lower Saxony Public Health Department initiated a study of this case in the Weser-Ems government district to investigate the spread of EHEC by children and their supervisors in kindergartens receiving certified raw milk supply. This established that there were ten kindergarten children in the Ammerland rural district who were asymptomatik EHEC carriers. The Local Public Health Department immediately carried out the necessary epidemic hygiene measures. First of all, control investigations were performed on the affected children, including environmental investigations on their families and contracts. The results of these investigations revealed the need to carry out additional environmental investigations in two kindegartens (follow-up investigations) as well as amongst employees in a hospital canteen. Within the families, a mother of an affected child was also identified as another asymptomatic EHEC carrier. However, the strains that were isolated reflected different serotypes. In total, the investigation of 337 people in contact with the eleven asymptomatic EHEC carriers did not confirm any person-to-person transmission--even though three of the kindergarten children shedding the organisms for 6-10 weeks attended the kindergartens for at least 4 weeks. No EHEC disease occurred in the communal facilities, neither were any positive cases identified by additional control investigations. The results indicate a probable lower rate of infectiousness by healthy EHEC carriers than was previously thought to be the case. Further studies are needed to decide if in future one should proceed on a case by case basis when considering the reauthorization of affected children and other people to enter communal facilities.