Quantitative Risk Assessment for Listeria monocytogenes in Cantaloupe

Introduction: The multistate listeriosis outbreak associated with cantaloupe in 2011 has drawn increasing concern and scrutiny on the melon production chain. Recent advances of quantitative microbial risk assessment (QMRA) provide a systematic and objective way to evaluate the food safety risk within the “farm-to-fork” continuum. However, no QMRA has been developed for melons, limiting the ability to provide quantitative guidelines.

Purpose:  Based on data from the published scientific literature and industry practice, a QMRA model was developed for Listeria monocytogenes associated with either fresh-cut or whole cantaloupe consumption. 

Methods:  A simulation model describing exposure and public health assessment from cantaloupe consumption was developed using the @RISK software. Relevant steps in the farm-to-fork chain were included. The baseline model assumed a prevalence of 1% and an initial level of L. monocytogenes contamination of -1 log CFU/cm² of. Variability and uncertainty in variables and parameters using a Monte Carlo framework with Latin Hypercube resampling and 10⁵ iterations.

Results: The model predicted the risk per serving of fresh-cut cantaloupe consumption to be approximately 10-fold higher than that of whole cantaloupe consumption. The estimated annual Listeriosis cases associated with fresh-cuts cantaloupe consumption in the U.S. among susceptible and general healthy population were 0.3 and 0.001 cases per year, respectively. The sensitivity analysis highlighted that temperature at retail and at household storage are the two most important factors affecting risk associated with fresh-cuts consumption, while household storage after cutting is the main factor for whole melon consumption. 

Significance: This study provides a first quantitative framework to evaluate the impact of contamination by L. monocytogenes in the farm-to-fork cantaloupe supply chain, and to assess potential risk reduction strategies.