Acknowledgements
The following investigators are members of the PirkanmaaWaterborne Outbreak Study Group: JJ Antonen, P Collin, J Helenius, J Herrala, T Katto, M Korpela, E Kujansuu, AL Kuusela, M Kuusi, J Laine, J Lumio, S Mustajoki, J Mustonen, H Oksa, P Ruutu, S Räsänen, and T Uotila. This study was supported financially by the Competitive Research Funding of Tampere University Hospital (Grants 9L002, 9M124, and 9P023).