Food Protection Trends - September/October 2022 - 384

Listeria has reservoirs in soil, forage, water, and infected
domestic and wild animals; its main route of transmission is
via the consumption of contaminated food. The main food
types likely to give rise to infection in the EU remain fresh
produce, raw milk products, and ready-to-eat (RTE) fish, meat,
and dairy products, which have been primarily contaminated
after processing (8).
The number of confirmed cases of listeriosis in the EU from the
latest available figures (8) and for the previous 10 years (compiled
from previous annual European Food Safety Authority Zoonosis
Reports), together with the infection rate per 100,000 people, are
shown in Table 1. It is recognized that the confirmed case numbers
are a slight underestimate of the actual total number of cases. Listeriosis
is the most important food poisoning disease in Europe; in
a typical year, there are more deaths from listeriosis than from all
other notifiable food poisoning organisms combined (including
Salmonella, Escherichia coli STEC infections, Campylobacter, and
Yersinia) (7).
The data in Table 1 indicate that the number of listeriosis
cases has leveled off over the last 5 years after significantly
increasing during the previous 5 years. Between 2010 and
2020, the EU population increased from approximately 440
million to 447 million (approximately a 1.6% rise). However,
the proportion of the population that are over 65 has risen
from 17.6 to 20.6% (approximately a 17% rise) in the same
period (10). Although the overall incidence of listeriosis is
low in Europe, its incidence expressed as a rate per 100,000
people is increasing, probably due to the expansion of the
section of the population above 75 years of age, the age group
with the highest incidence of listeriosis (7). As the European
population ages further, the importance of listeriosis will likely
increase; and, thus, more effort is needed from all stakeholders,
including the food industry and medical practitioners, to
control this disease.
Historical control of Listeria
The control of Listeria in food manufacturing is multifaceted
and has historically been achieved by product development,
product decontamination, hygienic zoning of factories,
effective cleaning practices, and management of the storage
and distribution chain.
Product design challenges the formulation of a food
product to minimize the presence of Listeria in the raw
materials and/or reduce the chance for any Listeria present
in the product after the decontamination process to survive
and grow. Raw material risk assessment is undertaken to
choose ingredients and suppliers so as to minimize the risk
of agricultural and primary processing contamination. The
majority of RTE products will have received a microbiological
reduction treatment by the product manufacturer, either as
a pasteurization (e.g., cooking) or a decontamination (e.g.,
produce washing ) process. Food manufacturing facilities are
built to contain hygiene zones such that, as the product is
processed and microbiologically decontaminated, the hygiene
384 Food Protection Trends September/October
of the process environment increases so that, after final product
decontamination, any further manipulation of the product
prior to packaging is undertaken in the highest hygiene zone.
The high hygiene zone, primarily for the manufacturing of
RTE products, is constructed to minimize the chance of crosscontamination
of Listeria from the processing environment by
reducing both potential Listeria harborage sites (sources) and
cross-contamination vectors to the exposed product.
Validated interim and end-of-production cleaning and
disinfection programs, together with periodic deep cleans in
which the equipment and building fabric is further dismantled
prior to cleaning, ensure that any Listeria pathogens entering
the high hygiene area during production periods are effectively
removed. Following packaging, some RTE products will
be designed to prevent Listeria growth (by the addition of
preservatives or modified in-pack atmospheres) or eliminate
the organisms in packed product via secondary, in-pack
pasteurization treatments (e.g., high-pressure processing). For
RTE products not preserved or in-pack treated, Listeria is likely
to be controlled by a chilled distribution and retail chain with
defined times and temperatures, within a shelf life determined
from practical or modeled trials that ensures Listeria is unlikely
to reach levels that are outside legislated values (2).
As noted in Table 1, Listeria cases are not being reduced
in the EU; and, thus, it can be argued that traditional control
methods are not sufficiently robust and that a new approach to
Listeria management is required. Hazard analysis and critical
control point (HACCP) (5) remains the primary food control
in Europe, and, in practice, any product decontamination steps
will be identified as critical control points (CCPs). There is
little or no evidence in published literature or the European
Rapid Alert System for Food and Feed (6) of any failures in
these CCPs giving rise to Listeria food poisoning incidents.
It would appear that, globally, the majority of Listeria cases
are caused by an excessive load or challenge of Listeria prior
to any decontamination process (e.g., in recent cantaloupe
cases (4, 11)) and by instances in which the decontamination
process may not be sufficiently effective at eliminating Listeria
(e.g., produce washing that may have a 1- to 2-log reduction
factor) or by cross-contamination after the decontamination
process (e.g., the world's largest known Listeria outbreak in
South Africa associated with cooked meats (19)). As such,
Listeria is primarily controlled by HACCP prerequisite
programs, and a better approach is required in which all
identified prerequisites are risk assessed and managed
according to their risk in a focused Listeria control plan.
Legislation on Listeria control
International and national legislation with respect to food
pathogens is established with the best intentions of reducing
the chance of a pathogen being present in foodstuffs at a level
likely to cause harm when consumed. However, different
approaches will be apparent with respect to guidance on
regulated control measures and, particularly, limits for the
Food Protection Trends - September/October 2022

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