An Overview of Traceback Investigations and Three Case Studies of Recent Outbreaks of Escherichia coli O157:H7 Infections Linked to Romaine Lettuce

Abstract

Leafy greens contaminated with Shiga toxin-producing Escherichia coli (STEC) have continued to cause foodborne illness outbreaks in recent years and present a threat to public health. An important component of foodborne illness outbreak investigations is determining the source of the outbreak vehicle through traceback investigations. The Food and Drug Administration is home to traceback investigation experts that employ a standardized process to initiate, execute, and interpret the results of traceback investigations in collaboration with the Centers for Disease Control and Prevention and state and local partners. Traceback investigations of three outbreaks of STEC infections linked to romaine lettuce in 2018 and 2019 were examined to demonstrate challenges, limitations, and opportunities for improvement. The three outbreaks resulted in a total of 474 illnesses, 215 hospitalizations, and five deaths. These illnesses were linked to the consumption of romaine lettuce from three distinct growing regions in Arizona and California. Some of the challenges encountered included the time it took to initiate a traceback, limited product-identifying information throughout the supply chain, lack of interoperability in record keeping systems, and co-mingling of product from multiple suppliers. These challenges led to time delays in the identification of the farm source of the leafy greens and the inability to identify the root cause of contamination. Implementation of technology enabled traceability systems, testing of these systems, and future regulations to incentivize adoption of traceability systems are some of the initiatives that will help address these challenges by improving traceback investigations and ultimately preventing foodborne illnesses and future outbreaks from occurring.

Bi-national outbreak of Salmonella Newport infections linked to onions: the United States experience

“…The U.S. Food and Drug Administration (FDA) and local and state regulatory agencies, including the California Department of Public Health (CDPH) and California Department of Food and Agriculture (CDFA), conducted traceback activities to identify common suppliers of suspect food items. Traceback activities are defined as the ‘process of reviewing product supply chain records to identify the origin of food served or sold at a specific point of service (POS)’ [ 4 ]. Information related to ill people's food exposures, including purchase dates and locations were collected during sub-cluster investigations and used to determine the ultimate source(s) of foods supplied to the point of sale.…”

“…Records including receipts, invoices, bills of lading and other relevant product traceability documents were obtained from restaurants associated with sub-clusters. A traceback leg was defined as the ‘supply chain for a specific illness sub-cluster or single case exposure, initiated at the POS.’ [ 4 ]…”

“…A traceback leg was defined as the "supply chain for a specific illness sub-cluster or single case exposure, initiated at the POS." [4] Field Investigations FDA, CDPH, and CDFA investigators conducted on-farm investigations and sample collections at locations identified in traceback, including farms, packing facility, public lands, and canals. Investigators conducted record reviews, interviews, and made observations on environmental factors, adjacent land use, and growing and harvesting practices (e.g., planting, irrigation, soil amendments, water, animal activity).…”

“…Raw produce items can be served in a variety of dishes, such as in salads and on sandwiches which often contain various other raw produce ingredients that may be difficult for ill people to remember. Traceback of raw produce items to their field of origin, particularly for those that can be purchased in bulk and without labelling, can be difficult [ 4 ]. Finally, the short shelf-life of many raw produce items can limit opportunities for testing leftover foods to identify the outbreak strain.…”

Prevalence, distribution, enterotoxin profiles, antimicrobial resistance, and genetic diversity of Bacillus cereus group isolates from lettuce farms in Korea

“…Since lettuce is primarily consumed fresh without cooking as a wrap material or in salads, it could potentially be contaminated with pathogens across the food supply chain and may cause illness upon consumption ( Bozkurt et al, 2021 ). The foodborne pathogens Escherichia coli O157:H7, Listeria monocytogenes , Salmonella, and Bacillus cereus are reported to be the major sources of lettuce-related outbreaks ( Kim et al, 2012 ; Irvin et al, 2021 ; Qu et al, 2021 ). A total of 60 outbreaks related to consumption of leafy vegetables, mainly lettuce was reported to the Centers for Disease Control and Prevention (CDC) between 2014 and 2021 [ Centers for Disease Control and Prevention (CDC), 2022 ].…”