A quantitative risk assessment (QRA) model was developed to evaluate the risk of invasive
listeriosis from the consumption of non-ready-to-eat (non-RTE) frozen vegetables. On a lot basis,
the QRA model simulates Listeria monocytogenes concentration and prevalence in a “Processing
module” that comprises blanching, potential recontamination and packaging, any post-packaging
inactivation treatment, and within-lot end-product testing and in a subsequent “Consumer’s handling
module” that encompasses portioning of frozen vegetables, defrosting, and cooking. Based on
available published data, the model was coded in nine sequential R functions designed to assess the
effectiveness of blanching, the improvement in processing environment hygiene, the implementation
of sampling schemes at the end of processing, and improved consumer instructions on the product’s
package. In a reference scenario, the model estimated that 9.4% of 500 g packages of frozen vegetables
would be contaminated, although at mean levels lower than 10 CFU/g, and assuming that 20% of the
portions of frozen vegetables would be left to thaw at room temperature for 2 h, the lot-level mean
risk of listeriosis in the susceptible population would be 2.935 × 10−14 (median 5.446 × 10−15) for
uncooked 50 g servings and 2.765 × 10−17 (median 5.184 × 10−18) for cooked 50 g servings. Analysis
of selected scenarios suggested that not cooking the non-RTE product contributes to the risk to a
greater extent than the level of contamination in the incoming raw vegetables, the latter in turn being
more influential than the level of contamination in the processing environment. The QRA model
is freely available as an R package with full documentation and can be used as a tool to inform the
consideration of strengthened risk management measures in view of the current changes in consumer
behavior and new diet trends.
