The tool (Excel-document, 189Kb) can assist in discriminating potential food-related norovirus outbreaks requiring source-tracking from the bulk of norovirus outbreaks caused by person to person tranmission and requiring different prevention and intervention measures.
A description of the tool can be found in:
Selection tool for foodborne norovirus outbreaks
Verhoef LPB, Kroneman A, van Duynhoven Y, Boshuizen H, van Pelt W, Koopmans M, et al. Emerging Infect Dis. 2009 Jan.