section). Important considerations are that sporadic cases will often go
undetected,since the focuswiththis methodis on larger incidents. Moreover,
it is oftendifficult to gather all relevantdetailsof an outbreak, because of the
timebetween the momentof consumption and the investigation.
An example of the second approach can be foundin a studyby Haldet al.
(2002)whocomparedvarioustypes of salmonellaein patientswithtypesin
various foodproducts, resultingin estimatesof the contributionof thesefood
products to the diseaseburden (Fig.2.4). An example of the thirdapproach
concerns the use of quantificationto determine the importance of variousroutes
of contamination. Evers et al. (2004)determined the contribution in the
exposure ofCampylobacterof variousroutes.Thistypeof quantificationcan
effectivelyhelpto target interventions. The veryextendedFDA/FSIS(Foodand
Drug Administration/FoodSafetyInspection Service)risk assessment(HHS/
USDA, 2003)concerningthe relativerisksofListeriamonocytogenesin ready-
to-eat foodsresulted in the identification of the mostimportantproduct groups.
Delimeats were identified as largelythe most important source,followed
unexpectedly by pasteurised milk.In this product, the risk per servingis not very
high,but owingto the largenumber of consumedunitsfor the per annumrisk,
and thusthe number of casesin a year,it is a relevant source. Thelow
prevalenceofListeriain this product is probablycausedby recontamination
(HHS/USDA, 2003).
Fig. 2.4 Estimatednumberof sporadicand domesticcasesof humansalmonellosisin
Denmarkin 1999attributedto differentanimal-foodsources(Haldet al., 2002).
36 Handbookof hygiene controlin the foodindustry