Almost Half Of All Listeria Illnesses Linked To Dairy Products: IFSAC Report

Almost half of all Listeria monocytogenes illnesses over the 1998-2017 period were attributed to dairy products, according to a recent report from the Interagency Food Safety Analytics Collaboration (IFSAC).

The IFSAC is a tri-agency group created in 2011 by the Centers for Disease Control and Prevention (CDC), the US Food and Drug Administration (FDA) and USDA’s Food Safety and Inspection Service (FSIS).

IFSAC has developed a method to estimate the sources of foodborne illness using outbreak data from 1998 through the most recent year (in the case of this report, that is 2017) for four priority pathogens: Listeria monocytogenes, Campylobacter, Escherichia coli 0157, and Salmonella.

These are considered priority pathogens because of the frequency (estimated 1.9 million illnesses each year combined) and severity of illness they cause, and because targeted interventions can significantly reduce these illnesses.

Data for the report came from 1,329 foodborne illness disease outbreaks that occurred from 1998 through 2017 and for which each confirmed or suspected implicated food fell into a single food category. The method relies most heavily on the most recent five years of outbreak data (2013-2017).

Of the 1,329 outbreaks used in the analysis, 811 caused or suspected to be caused by Salmonella, 242 by E. coli 0157, 40 by Listeria, and 236 by Campylobacter. Due to down-weighting, the last five years of outbreaks provide the majority of information for the estimates; outbreaks from 2013 through 2017 provide 72 percent of the model-estimated illnesses used to calculate attribution for Salmonella, 62 percent for E. coli 0157, 79 percent for Listeria, and 58 percent for Campylobacter.

Over 77 percent of Listeria monocytogenes illnesses were attributed to dairy products and fruits, including 48.4 percent attributed to dairy. The credibility intervals for the dairy and fruits categories were quite wide, due to the small overall number of outbreaks (40).

Nearly 80 percent of non-dairy Campylobacter illnesses were attributed to chicken, other seafood, turkey, and other meat/poultry.

A Campylobacter attribution percentage for dairy is not presented in the report partly because most foodborne Campylobacter outbreaks were associated with unpasteurized (raw) milk, which is not widely consumed, the report noted.

The attribution percentages before removing dairy were: dairy, 62.6 percent, chicken 17.9 percent, other seafood 4.6 percent, turkey 3.7 percent and other meat/poultry 3.3 percent, and were less than 2 percent for each of the other categories. The chicken attribution percentage increased to 47.9 percent after removing dairy.

Almost 75 percent of E. coli 0157 illnesses were attributed to vegetable row crops (such as leafy vegetables) and beef. Some 6.6 percent of E. coli 0157 illnesses were attributed to dairy products.

Over 75 percent of Salmonella illnesses were attributed to seven food categories: seeded vegetables (such as tomatoes), chicken, fruits, pork, eggs, other produce, and beef. Some 4.3 percent of Salmonella illnesses were attributed to dairy products.

This report addresses several issues with outbreak-based foodborne illness source attribution, yet limitations associated with generalizing outbreak data to sporadic illnesses remain and

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