In the hazard characterisation step, a dose±response relationship was
described, as a percentageof eachage-basedgroupthat will become seriously ill
or die afterbeingexposedto a particular levelofL. monocytogenes. The dose±
responserelationship was estimated fromliteraturedata on listeriosisoutbreaks
and fromstudies withanimals. In therisk characterisationstep, the resultsof the
exposure assessmentand the hazardcharacterisation werecombinedto estimate
the likelihood of adversehealtheffects. Thiswas doneby running Monte Carlo
simulations withstatisticaldata resultingfromthe exposure assessmentand the
hazardcharacterisation.
Resultsfromthe risk assessment showed that the risk of listeriosison bothper
servingand per annumbasisvaries greatlyamong the variouscategories. The
category delimeats' rankedas highest risk on bothper servingand per annum basis,withestimated risksbeing7.7 10 ˇ^8 casesper serving or 1599casesper year.Thecategoriespasteurised fluidmilk'and highfat and otherdairy products' rankedmoderate risk on a per servingbasis(about 2 10 ˇ^9 casesper serving)but ranked highriskon a per annum basis(about 70 cases/year), because of the highyearly consumption of theseproducts. Hard cheeseranked low risk on bothper serving and per annumbasis,withestimatedrisksbeing 4.5 10 ˇ^15 cases per serving or <0.1casesper year. The risk assessmentalso showed thatsusceptible subpopulations (suchas the elderly,perinatal and individualswithchronic illnesses) are muchmorelikelyto contractlisteriosis thanthe general population.Thissuggests thatstrategiestargeted to these susceptible groups would result in the greatest reduction in public health impact. Finally, the risk assessmentmodelwas usedto calculate somewhatif?'
scenarios to estimate the likelyimpact of controlstrategies for foodborne
listeriosis. It was,for example, calculatedwhat the impactwould be if home
refrigerators couldnot operateaboveeither45 ÎF (7.2 ÎC) or 41 ÎF (5 ÎC). These
scenarios predictedthat the totalnumberof cases of listeriosiswould be reduced
from 2105 to 656 cases per year by ensuring that all homerefrigeratorsoperated
at 45 ÎF or less. Thenumber of caseswouldreduceto 28 per year(a 98%
reduction) if homerefrigerators wouldalwaysoperatebelow41 ÎF. Similarly it
was shownthat reduction of storagetime (shelf-life)for deli meatfrom28 days
to 14 daysreduces the numberof cases of listeriosis in the elderlypopulationby
13.6%. In another set of `whatif?' scenarios it waspredicted that a 1 log
reduction in contaminationat retailwould reducethe number of predictedcases
in the elderly populationby 50%;a 2 log reductionwouldresultin 74% less
cases.
20.3.2 Productionline for pasteurised milk
Mostfoodprocessors havecarried out risk assessments of some kindon their
production lines,often as part of a HACCP plan.Although suchrisk assessments
are widely performed,veryfew of themare published owingto the confidential
information contained in such assessments. The example given below is
Riskassessmentin hygiene management 317