A US Food and Drugs Administration (FDA) report has confirmed that environmental samples taken from packaging equipment and a cold storage unit at Jensen Farms tested positive for the four outbreak-associated strains of Listeria monocytogenes.
The report provides an overview of factors which led to the deaths of 25 people and the infection of a further 123 across 26 states
The foodborne outbreak, the worst in the US since 1998, has been attributed to infected Jensen Farms Rocky Ford brand whole cantaloupes.
The aim of the report was to “identifying the factors that potentially contributed to the introduction, growth, or spread of the Listeria monocytogenes strains that contaminated the cantaloupe.”
Environmental samples collected at Jensen Farms suggested it was “likely that the contamination occurred in the packing facility. It is also likely that the contamination proliferated during cold storage.”
Pools of water, formed by a refrigeration drain, were found to be positive for one of the outbreak strains of Listeria.
Officials have also suggested that the design of the packaging facility made cleaning the refrigeration drain difficult, which the report suggests may have served as a “harbourage site” for the pathogen.
Recently purchased packaging equipment, previously used in the production of another raw agricultural commodity, has also been submitted as a factor.
The equipment, some of which was used for the washing and drying of cantaloupes wasn’t “easily cleanable and was previously used for handling another raw agricultural commodity with different washing and drying requirements, Listeria monocytogenes could have been introduced as a result of past use of the equipment.”
“Environment ideal for Listeria”
Officials have also identified a truck used to transport culled cantaloupe to a cattle operation, and condensation formation as potential contaminants.
Condensation formed on the whole cantaloupes would have provided an “environment ideal for Listeria monocytogenes growth.”
Field heated cantaloupes were not pre-cooled at Jensen Farms before being washed and placed in cold storage which would have “potentially created conditions that would allow the formation of condensation.”
Samples of soil, animal excrement, furrow drag swabs, agricultural and pond water and cantaloupes from the fields were also collected, but all were found to be negative for Listeria.
The pathogen is traditionally associated with ready-to-eat and processed food products such as deli meats, unpasteurised cheese, raw milk and fresh-cut fruit and vegetables.
“This is the first Listeriosis outbreak associated with a whole fruit or vegetable raw agricultural commodity,” added the report.
The report concluded: “FDA’s findings regarding this particular outbreak highlight the importance for the industry to employ good agricultural and management practices in their packing facilities as well as in growing fields.”