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US risk ranking of ready-to-eat foods

The USDA and FDA have jointly released a draft risk ranking for ready-to-eat foods that might be contaminated with Listeria monocytogenes.

While listeriosis is comparatively rare in Australia, when the disease does occur the consequences may be very serious in sub-groups of the population (Food Safety & Hygiene, November 1998). The US risk assessment takes into account three age-based groups:
  • perinatal. These are pregnancy associated cases where the mother experiences a foodborne L. monocytogenes infection during pregnancy exposing her fetus to the pathogen.
  • elderly. This group includes people 60 or more years of age. People in this age bracket are considered to have increased susceptibility to listeriosis.
  • intermediate age. This group includes the entire remaining population. Healthy people appear not to be very susceptible to severe illness from L. monocytogenes. There are certain subpopulations within this group that are more susceptible to listeriosis. However there is insufficient data to separate this group further.

The aim of the risk ranking which took two years to complete was to identify which ready-to-eat foods pose the greatest risk to consumers particularly those susceptible to the organism. Twenty products were included in the ranking and those included foods in the categories of seafood, fruit and vegetables, dairy, meats and combination foods.

When foods were considered by the ranking body on a per-serving basis, the foods ranked most likely to transmit listeriosis were pâté, fresh soft cheeses, smoked seafood and deli meats. This ranking accords closely with warnings to susceptible groups issued by local health authorities.

When the amount of each food consumed each year by Americans i.e. the consumption pattern, was included in the ranking, deli meats rose from fourth to first. They were followed by deli salads (sixth on a per-serving basis) and pasteurised milk – presumably as a result of post-pasteurisation contamination. Pâtés, soft cheeses and smoked seafood moved down the ranking list moderately.

The report concludes that while the exposure assessment suggests that US consumers are exposed to low levels of L. monocytogenes on a regular basis, the likelihood of acquiring listeriosis is extremely small. Risk factors to be taken into account include:
  • how much of the food is consumed
  • how many organisms are on the food
  • whether the organism can grow
  • the temperature at which the food is stored
  • how long the food is stored before it is eaten.
Food Safety and Hygiene
Prepared by Keith Richardson and Beverley George
Food Science Australia
PO Box 52, North Ryde 1670. Tel +61 2 9490 8397 Fax +61 2 9490 8499
Email enquiries@csiro.au