Listeriasis is a food born disease caused by Listeria Monocytogenes

1. Listeria monocytogenes:
food as public health risk
Silvia Pessah-Eljay. MD., MPh., MS.
Epidemiology Division. Public Health Service.

2. 2
Objective of this session
Understand that Listeria monocytogenes it
is not only a matter of food quality / safety
criterion,
first of all,
Is the significance of a public health risk.

3. 3
Listeria monocytogenes
• Gram(+) bacteria
• Regular, short rods with
rounded ends
• Facultative anaerobes
• Can grow at refrigeration
temperatures to significant
numbers (in sufficient time)
• Resistant for low pH
• Are known 11 serotypes
• 1/2 a, 1/2 b, 1/2 c,
3a, 3b, 4a, 4 ab, 4 b,
4c, 4d, y 4e
• The antigenic
determinants of Listeria
monocytogenes, have
cross reaction with gram
positive bacteria such as:
Corynebacterium, Staphylococcus
aureus and enterococos.

4. 4
Listeria monocytogenes
• The primary reservoir for L.
monocytogenes are soil, water and mud
• Additional reservoir is alimentary tract of
domestic and wild animals
• Consumption of contaminated food is the
main route of infection for human
• Infectious dose was determined as 107
CFU (some papers suggest 102 CFU!!)

5. 5
• Listeriosis: Infectious disease,
caused by Listeria monocytogens
• Especially in danger are some
groups of people (high risk
groups):
• Neonates,
• Pregnant women,
• Immunocompromised
people,
• Elderly
Listeria monocytogenes

6. 6
Transmission of L. monocytogenes
Reservoir Source Vehicle
Transplacentary
infections

7. 7
L. monocytogenes in food processing and retail
▪ L. monocytogenes is frequently present in raw foods of plants and animal
origin
▪ Can be found in food processing environments
▪ Present in food retail environment and household

8. 8
Notificable disease.
▪ Varied clinical forms are described:
▪ Asymptomatic (subclinical)
▪ Symptomatic:
▪ Localized infections
▪ Self limited gastrointestinal disease
▪ Systemic manifestations
▪ Sepsis
▪ CNS infections
▪ Endocarditis
▪ Pregnancy associated infections
Listeria monocytogenes

9. 9
Gastrointestinal listeriosis
▪ Usually self-limiting febrile gastrointestinal
disease presenting with unspecific symptoms
like:
▪ Nausea
▪ Vomiting
▪ Diarrhea
▪ Observed as sporadic cases and food-poisoning
outbreaks.
Listeriosis

10. 10
Outbreaks of listeriosis
Food-borne outbreak: “an incidence, observed under given
circumstances, human cases of the same disease and/or infection,
or a situation in which the observed number of human cases
exceeds the expected number and where the cases are linked, or
are probably linked, to the same food source”. (Directive 2003/99/EC)
Food vehicle: food (or foodstuff) that is contaminated by a
causative agent.
(EFSA, Manual for reporting of food-borne outbreaks […])

11. 11
Outbreaks of listeriosis
Listeria monocytogenes is absolute foodborne pathogen, caused both:
gastrointestinal and invasive disease

12. 12
Outbreaks of listeriosis
Country Year Food vehicle Affected
Austria,
Germany,
Czech Rep.
2009 Acid curd cheese “Quargel” 14 cases, 4 deaths
USA,
Louisiana
2010 Hog head cheese 14 cases of invasive listeriosis
USA
(multistate)
2011 Cantaloupe (Rockmelon) 84 people, 15 deaths
USA
(multistate)
2014 Caramel Apples 35 people, 7 deaths
USA
(multistate)
2015 Bell Creamery Products 10 cases, 3 deaths

13. 13

14. 14
Pregnancy associated listeriosis
▪ Case classification: illness occurred in a pregnant woman or an infant
aged <28 days
▪ Woman has unspecific flu-like symptoms
▪ CNS infection are very rare in pregnant women
▪ Outcome depends on stage of pregnancy
I trimester II trimester III trimester
Congenital listeriosis
Preterm birth
Stillbirth
Miscarriage
Data Source: ECDC TESSY

15. 15
Congenital listeriosis
Early-onset Late-onset
Associated with prematurity and
acquired through utero.
Caused by bacteria acquired from vaginal
tract of asymptomatic mothers
Clinical symptoms occurs just after birth
(mean-time is 1.5 day)
Occurs about 2 weeks post partum.
Sepsis Meningitis
• Depending on time of clinical symptoms manifestation, two types of
infection are recognized

16. 16
Listeriosis cases by year. Israel. Data belongs to the Epidemiology Division.
Ministry of Health of Israel
Epidemiology Division. Public Health Service. Ministry of Health. 2015
* Cases of 2015 only at end of May.
0
10
20
30
40
50
60
70
19961997199819992000200120022003200420052006200720082009201020112012201320142015
Case number of Listeriosis. 1996 - 2015

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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
19961997199819992000200120022003200420052006200720082009201020112012201320142015*
Incidence x 100000 0.10.10.60.40.20.70.30.30.40.30.50.80.50.40.60.50.70.70.70.3
Incidenceratex100,000
Listeriosis rates. Israel. 1996-2015
Listeriosis rates by year. Israel. Data belongs to the Epidemiology Division.
Ministry of Health of Israel
Epidemiology Division. Public Health Service. Ministry of Health. 2015

18. 18
Age distribution of Listeriosis. Israel. Data belongs to the Epidemiology Division.
Ministry of Health of Israel
0
2
4
6
8
10
12
14
16
<1 1-14 15-44 45-64 65+
Comparison of number of cases by age groups.
(Only from January to May)
2013 2014 2015
0
5
10
15
20
25
30
35
40
>1 1-14 15-44 45-64 65+
Comparison of number of cases by age groups.
2013 2014 2015
Epidemiology Division. Public Health Service. Ministry of Health. 2015
Who belongs to this group?
• Pregnant women
• Cancer & terminal diseases
• Systemic no-terminal diseases

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Severity of listeriosis
▪ Characterization of listeriosis severity depends on category of
disease (invasive / non-invasive).
▪ Low occurrence contrasts with high case-fatality rate (ranging
20-30%).
▪ Up to 11% of neonates and 30% survivor of CNS infections
suffer residual symptoms.
▪ Psychiatric residual symptoms have been also reported.

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“Non missing points” in the Epidemiological Research Form

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22. 22
Listeriosis cases EU in 2010-2012 by country
http://ecdc.europa.eu/en/publications/Publications/food-and-waterborne-diseases-surveillance-report-2015.pdf

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Risk assessment
The risk assessment was tailored to address three specific questions posed by the 33rd
session of the CCFH (CAC, 2000) namely:
1. Estimate the risk of serious illness from L. monocytogenes in food when the number of
organisms ranges from absence in 25 grams to 1000 colony forming units (CFU) per
gram or millilitre, or does not exceed specified levels at the point of consumption.
2. Estimate the risk of serious illness for consumers in different susceptible population
groups (elderly, infants, pregnant women and immunocompromised patients) relative
to the general population.
3. Estimate the risk of serious illness from L. monocytogenes in foods that support its
growth and foods that do not support its growth at specific storage and shelf-life
conditions.

24. 24
Risk assessment to public health from foodborne L. monocytogenes
▪ The goal was to predict the relative
public health impact of foodborne
Listeria monocytogenes from selected
food categories.
▪ RTE foods to asses are chosen, if had a
history of either Listeria monocytogenes
contamination or were implicated
epidemiologically.
▪ This risk assessment have been used as
base for FAO WHO recommendations.

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Cultured Milk Products
Hard Cheese
Ice Cream and Other Frozen
Dairy Products
Processed Cheese
Preserved Fish
Raw Seafood
No food categories
High Fat and Other Dairy Products
Pasteurized Fluid Milk
Soft Unripened Cheese
Pâté and Meat Spreads
Unpasteurized Fluid Milk
Smoked Seafood
No food categories
Deli-type Salads
Dry/Semi-dry Fermented Sausages
Frankfurters (reheated)
Fresh Soft Cheese Fruits Semi-soft
Cheese Soft Ripened Cheese
Vegetables
No food categories
Cooked RTE Crustaceans No food categories
No food categories
Deli Meats
Frankfurters (not reheated)
DecreasedRiskperServing
Decreased Risk per Annum
Moderate riskHigh risk Low riskVery high risk Very low risk
Risk assessment - results

26. 26
Risk assessment - results
Food
Cases of listeriosis
per million people
per year
Cases of listeriosis
per 1 millon
servings
Milk 9.1 0.005
Smoke fish 0.46 0.021
Ice cream 0.012 0.0004
The mean risk estimates of the number of illnesses per 1million people per
year and the risk per serving for 3 ready-to-eat foods.

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Foods of very high risk
▪ Includes two food categories:
▪ Deli Meats (included smoked fish)
▪ Frankfurters, Not Reheated.
▪ They have high predicted relative risk rankings on both a per
serving and per annum basis, because:
▪ Have relatively high rates of contamination.
▪ Support the relative rapid growth of Listeria monocytogenes
under refrigerated storage.
▪ Are stored for extended periods.
▪ Are consumed extensively.
▪ These products have also been directly linked to outbreaks of
listeriosis.

28. 28
Foods of very high risk
This risk designation is one that is
consistent with the need for
immediate attention in relation to
the national goal for reducing the
incidence of foodborne listeriosis.
Likely activities include the
development of new control
strategies and/or consumer
education programs suitable for
these products.

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Very low risk food products
Includes four food categories:
▪ Cultured Milk Products,
▪ Hard Cheese,
▪ Ice Cream and Other
Frozen Dairy Products,
▪ Processed Cheese.

30. 30
Very low risk food products
▪ These products all have in common the characteristics of being subjected to a
bactericidal treatment, having very low contamination rates, and possessing
an inherent characteristic that either inactivates Listeria monocytogenes (e.g.,
Cultured Milk Products, Hard Cheese) or prevents its growth (e.g., Ice Cream
and Other Frozen Dairy Products, Processed Cheese).
▪ This results in a very low predicted per serving relative risks. The predicted per
annum relative risks are also low despite the fact that these products are
among the more commonly consumed RTE products considered by the risk
assessment.
▪ The results of the risk assessment predict that unless there was a gross error in
their manufacture, these products are highly unlikely to be a significant source
of foodborne listeriosis.

31. 31
EU initiative for L. monocytogenes reduction in RTE foods
European Comission launched the survey on Listeria monocytogenes in selected
categories of ready-to-eat food at retail in the EU.
▪ RTE food categories under investigation:
▪ Smoked and gravad fish,
▪ Soft and semi-soft cheeses,
▪ Heat-treated meat products.
▪ Analyses methods:
▪ L. monocytogenes detection and enumeration,
▪ pH and aw measurement,

32. 32
Reduction of risk to public health from foodborne L. monocytogenes
Risk of
listeriosis
Consumer
susceptibility
Food matrix
Virulence of
the strain

33. 33
Summary
▪ Listeriosis is serious infectious foodborne disease
▪ Many factors affect the risk of listeriosis
▪ Initial quality of food - no Listeria at detectable level is the best
method to increase the food safety

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