1. 1Department of Food and Environmental Hygiene, Faculty of Veterinary Medicine, University of Helsinki, P.O. Box 57, FIN-00014 University of Helsinki, Finland
2. 2Finnair Catering, FIN-01053 Finnair, Finland
3. 3Vantaa City Food Inspection, Environmental Centre, Viertolankuja 4 A, FIN-01300 Vantaa, Finland