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Table 37: Temperature ºC, serving at random. Entries Mean [2.5, 97.5] uncertainty replicates.
Country Population
Uncertainty consideration
Mean 5
th
ile Median
95
th
ile Canada
Elderly Point estimate
4.5 0.3
4.5 9.1
Canada Elderly
Uncertainty
4.7 [4.4; 5.3] 0.35 [0.087; 0.60]
4.3 [4.2; 4.4] 9.6 [8.7; 16.0]
Canada Pregnant women
Point estimate 4.8
-0.22 4.3
11
Canada Pregnant women
Uncertainty 4.6 [4.4; 4.8]
-0.44 [-0.20; 0.18] 4.6 [4.4; 4.8]
12 [10; 17]
Canada General and
Immunocompromised Point estimate
4.5 -0.13
4.1 10
Canada General and
Immunocompromised Uncertainty
4.1 [3.9; 4.3] -0.13 [-0.33; 0.025]
4.1 [3.9; 4.3] 10 [9.5; 13]
U.S. Elderly
Point estimate
4.5 0.29
4.2 9.1
U.S. Elderly
Uncertainty 4.7 [4.4; 5.4]
0.35 [0.094; 0.61] 4.3 [4.2; 4.4]
9.6 [8.7; 16] U.S.
Pregnant women Point estimate
4.8 -0.21
4.4 11
U.S. Pregnant women
Uncertainty 5.1 [4.7; 5.8]
-0.20 [-0.46; 0.18] 4.6 [4.4; 4.8]
12 [10; 17] U.S.
General and Immunocompromised
Point estimate 4.5
-0.15 4.1
9.9
U.S. General and
Immunocompromised Uncertainty
4.6 [4.3; 5.1] -0.33 [-0.14; 0.03]
4.1 [3.9; 4.3] 10 [6.4; 13]
Contamination at Home
The microbiological literature suggests that contamination can occur in the consumer’s refrigerator when the cheese is stored, open, over several eating occasions. However, the
literature does not describe the frequency and level of contamination that would inform model inputs for that source of contamination.
7.5. L. monocytogenes Ingested in a Serving
All servings from non L. monocytogenes contaminated cheeses contain, by definition, 0 L. monocytogenes cells. For L. monocytogenes contaminated cheeses, consumption was modeled
as a partition process see section 6.3. Each contaminated cheese was considered as if it were a stack of contaminated and uncontaminated grams of “core” and “rind” cheese see section 6.1.
A serving of C grams was considered to be a random sample of these grams amongst the grams that constitute the cheese, using a hypergeometric distribution to describe variability among
servings and among cheeses. The L. monocytogenes present in these C grams were the ingested dose. Variability in the proportion of rind and core in a serving was not modeled.
This simulation process respects the clustering of L. monocytogenes among contaminated and uncontaminated cheeses and the clustering within contaminated cheeses.
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8. Risk Characterization Method
The risk characterization is the final component of the risk assessment. Risk characterization integrates the hazard characterization and the exposure assessment to synthesize the probability
and severity of adverse health effects in a particular population of consumers. In this risk assessment, the output of the risk characterization is the probability of invasive listeriosis
following the consumption of a random serving of cheese by an individual in a considered subpopulation and country. Using a second-order Monte-Carlo simulation framework, the
variability and uncertainty of the risk characterization outputs are estimated as a reflection of the variability and uncertainty of the model inputs. In addition, a sensitivity analysis is used to
explore the impact of the uncertainty and variability of inputs on the risk outputs.
8.1. Output of the Risk Characterization
The main output that will be used to assess the risk of invasive listeriosis from soft-ripened cheese consumption in Canada and the U.S. is the probability of invasive listeriosis following the
consumption of a random serving of cheese by an individual of the considered subpopulation.
We will simplify this output to the: risk per serving in the particular country Canada, U.S. for
the considered population Elderly, Immunocompromised, Pregnant, General. This output is of interest because the expected number of cases of invasive listeriosis in a particular population
during a specific period of time is proportional to the mean risk per serving. The average number of cases in N
c, p
servings is
p c
s p
c p
c
R N
C
,
, ,
× =
, where N
c,p
is the number of servings consumed by population p in country c during this period and
p c
s
R
,
is the mean risk per serving for this population p during this period of time
15
. For any risk mitigation strategy indexed 1 that does not impact the number of servings consumed in a population, the proportion of avoided cases
compared to the baseline pasteurized-milk cheese baseline or raw-milk cheese baseline -- indexed 0 is then equal to:
1 1
R R
C C =
.
15
under the assumption of a binomial result for the number of cases in N
c, p
servings.
