Food Protection Trends - May/June 2023 - 234

Modeling of the preharvest Salmonella transmission and
the impact of different interventions on human salmonellosis
cases is difficult, as numerous factors will affect interventions
and the impact on public health. In addition, interactions
between preharvest control and postharvest control
strategies may be complex. Prior risk assessments in this
space are limited but may provide some help with initial
development of more comprehensive risk assessments (1).
Some key considerations for the model structure include the
ability to model transmission of different serovars (rather
than all Salmonella); this is important, as there is clear
evidence that Salmonella subtypes differ in the ability to
cause human disease (16, 21, 28). In addition, vaccination
strategies are currently either specific to certain serovars (i.e.,
for autogenous vaccines) or differ in effectiveness against
different serovars (i.e., for live attenuated vaccines). Key data
needs for preharvest models (or preharvest compartments
of systems models) include not only the more obvious (e.g.,
prevalence of Salmonella and different Salmonella serovars
at the various preharvest stages; effectiveness of diverse
interventions, including uncertainty and variability), but also
data that may not always be considered as data needs and
that are likely to be more challenging to acquire. For example,
data on interactions between different Salmonella serovars at
preharvest, as well as data on the effectiveness of competitive
exclusion cultures to prevent Salmonella colonization
(including colonization by different subtypes) in the chick,
could be important to appropriately assess certain risk
management strategies, including potential unintended
consequences (e.g., where control of one Salmonella serovar
through vaccination may subsequently allow other serovars
that may or may not show enhanced human virulence to rise
in prevalence).
Risk management options at poultry slaughter and
processing
There are many risk management options that can be used
to reduce Salmonella loads and prevalence at slaughter and
further processing. Although these risk management options
would typically be equally effective against all Salmonella
( " generic risk management options " ), there are also some
risk management options that would target specific serovars
or groups of serovars. Generic risk management options
include different rinse treatments (e.g., with peracetic acid)
that have been shown to effectively reduce Salmonella loads
(20). However, some of these treatments may be more
effective against some serovars (e.g., those that typically
represent surface contamination) than others (e.g., those
that are preferentially located internally in tissues, such
as in joints). Another generic risk management option is
scheduling slaughter on the basis of the results of prior testing
in chicken houses, with live birds from houses with higher
loads or prevalence of all Salmonella or specific Salmonella
serovars of greater public health relevance to be slaughtered
234 Food Protection Trends May/June
at the end of a shift to reduce cross-contamination risks or
subjected to enhanced control strategies to reduce Salmonella
before slaughter. There are few subtype- or serovar-specific
interventions at slaughter and processing; one example of
such an intervention is the use of specific phages that target
specific subtypes or serovars (25).
To model the public health impact of different risk
management practices at slaughter and processing, reliable
data on the efficacy of different treatments are essential. Data
on treatment efficacy generated in commercial slaughter and
processing facilities are by far preferable over " laboratory "
data that are generated under artificial and simplified
conditions. Importantly, data on treatment efficacy should
also include information on variability and uncertainty to
be useful for modeling. In addition, data that quantify the
relative efficacy of treatment against different subtypes or
serovars in commercial operations would be important to
prevent over- or underestimation of the efficacy against
different subtypes. Similarly, data on prevalence, level, and
serotype distribution of Salmonella at key stages in processing
along with estimates of intervention effectiveness would
also be very significant. Models should also examine the
impact of selecting products with lower or higher Salmonella
contamination risks for particular end-product uses (e.g.,
Food Safety and Inspection Service [FSIS] data suggest
that mechanically separated raw materials lead to end
products with higher prevalence (35)). In addition, models
should include the ability to simulate lotting strategies,
using preharvest or preprocessing testing for Salmonella or
other indicators to selectively direct certain higher or lower
risk raw materials to different products. Models should
also include the ability to model transmission of different
serovars, which is particularly important with (i) emerging
interest in serovar- or subtype-specific Salmonella control
options at processing and slaughter (32) and (ii) emerging
evidence that Salmonella subtypes may differ substantially in
sensitivity to postharvest treatments.
Consumer risk management options
Observational studies and other research have documented
a high prevalence of high-risk consumer food handling
behaviors when preparing poultry (24, 31). Previous risk
assessments have sought to model how changes in food
handling practices might influence the number of Salmonella
infections caused by contaminated ground turkey (37)
and chicken parts (22). These models have considered
variables, including whether the product is cooked at home
or in a restaurant, exposure to Salmonella through crosscontamination
from raw poultry to other products and
exposure via consuming an undercooked product (22). The
significance of these variables differs by model. For instance,
Lambertini et al. note that " results were fairly insensitive to
changes in the fraction of undercooked portions, " which " is
likely due to the fact that a large fraction of undercooked
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