Atlanta, GA—The Interagency Food Safety Analytics Collaboration (IFSAC) recently released a report on foodborne illness source attribution estimates for 2016 for Listeria monocytogenes, Salmonella, Escherichia coli 0157, and Campylobacter.

IFSAC developed a method to estimate the sources of foodborne illness using outbreak data from 1998 through the most recent year for four priority pathogens: Salmonella, Listeria, E. coli 0157, and Campylobacter.

For IFSAC’s 2016 estimates, data came from 1,255 foodborne disease outbreaks that occurred from 1998 through 2016 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 (2012- 2016).

Foods are categorized using a scheme IFSAC created to classify foods into 17 categories that closely align with the US food regulatory agencies’ classification needs.

Each outbreak was assigned to a single food category using the IFSAC food categorization scheme based on confirmed or suspected implicated foods and ingredients (i.e., a single ingredient was confirmed or suspected to be implicated or all ingredients in the food were assigned to the same food category).

The study’s results are based on 762 outbreaks caused or suspected to be caused by Salmonella, 235 by E. coli 0157, 37 by Listeria, and 80 by Campylobacter (after 141 outbreaks due to dairy were excluded).

Estimated Salmonella and Campylobacter illnesses were more widely distributed across food categories than illnesses from E. coli 0157 and Listeria; most of the illnesses for the latter two pathogens were attributed to two food categories.

Over 75 percent of the Listeria illnesses were attributed to dairy and fruits; specifically, 45.3 percent were attributed to dairy and 30.6 percent were attributed to fruits. The credibility intervals for the dairy and fruits categories were quite wide, partly due to the small number of total outbreaks.

Although the limited number of outbreaks and wide credibility intervals dictate caution in interpreting the attribution percentage for dairy for Listeria, the risk to pregnant women and persons with weakened immune systems of consuming soft cheese made from unpasteurized milk or in unsanitary conditions is well-recognized, the report stated.

Among the 221 Campylobacter outbreaks during the study period, the 141 assigned to dairy were excluded from the final calculation of the attribution percentage due to the challenges of estimating Campylobacter attribution using outbreak data.

Most foodborne Campylobacter outbreaks were associated with unpasteurized milk, which is not widely consumed, the report noted (the unadjusted dairy attribution percentage for Campylobacter was 66.9 percent and was less than 10 percent for all other food categories).

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

An analysis of 38 case-control studies of sporadic campylobacteriosis found a much smaller percentage of illnesses attributable to consumption of raw milk than chicken. For example, a US Food- Net case-control study attributed 1.5 percent of campylobacteriosis cases to consumption of unpasteurized milk, compared with 24 percent to consumption of chicken prepared in a restaurant.

Structured expert judgment studies estimate about 8 to 10 percent of foodborne campylobacteriosis to be attributable to dairy products (principally raw milk), compared to 33 to 72 percent for chicken.

Over 75 percent of Salmonella illnesses were attributed to seven food categories; seeded vegetables (such as tomatoes), chicken, pork, fruits, other produce, eggs, and beef. Some 4.1 percent were attributed to dairy products.

Nearly 75 percent of E. coli 0157 illnesses were attributed to vegetable row crops. Some 7.8 percent were attributed to dairy.

Estimates should not be interpreted as suggesting that all foods in a category are equally likely to transmit pathogens, the report pointed out. Caution should also be exercised when comparing estimates across years, as a decrease in a percentage may result, not from a decrease in the number of illnesses attributed to that food, but from an increase in illnesses attributed to another food.

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