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Outbreaks, Alerts and Hot Topics

August, 2018

Foodborne diseases


Mary Anne Jackson, MD | Division Director, Infectious Diseases | Medical Editor, The Link Newsletter | Professor of Pediatrics

While strategies continue to evolve to improve food safety, a significant burden of disease remains, related to foodborne illness and is associated with health and economic consequences. First compiled and published in 1923, data related to foodborne disease outbreaks focused on infections specifically linked to milk. Reporting expanded to include all food products in 1938. More recent data is derived from FoodNet, which includes 10 sites compromising the Foodborne Disease Active Surveillance Network focusing on nine specific pathogens, and the Foodborne Disease Outbreak Surveillance System, which over the last six decades, utilizes a voluntary reporting system to identify foodborne illnesses that result in outbreaks.

Current estimates suggest that 15 percent of the U.S. population will annually develop a foodborne illness. While Salmonella, Campylobacter, Shigella, STEC and Cryptosporidium typically are associated with the most foodborne-related infections, the use of newer testing modalities suggest Cyclospora, Yersinia and Vibrio account for more cases than previously reported.1 

Published in MMWR this past month, results received to the Foodborne Disease Outbreak Surveillance System over the last seven years are used to characterize recent trends in foodborne disease outbreaks.2 Between 2009 through 2015, over 5,700 outbreaks occurred, with reports coming from all 50 states, the District of Columbia and Puerto Rico. The outbreaks accounted for 100,939 illnesses. 

Outbreak-associated illnesses were caused by a variety of bacterial, parasitic and viral pathogens, and some were linked to chemical and toxin etiologic agents. More than 25 bacterial pathogens, five parasites and five common viral agents accounted for most of the cases. The top three causes in each of those sub-groups included Salmonella, Shiga-toxin producing E. coli and Campylobacter, Cryptosporidium, Trichinella and Cyclospora and norovirus, hepatitis A and sapovirus. 

The two most common pathogens included norovirus, which accounted for 38 percent of the outbreaks, and Salmonella with 30 percent. Norovirus outbreaks were typically associated with ready-to-eat foods, like lettuce, fruits or mollusks, contaminated during food preparation by infected food workers. Salmonella outbreaks were associated with a variety of food products, many produced outside of the U.S. Hospitalizations occurred in 4 percent of outbreak cases overall, and there were 140 deaths, with 82 percent of deaths related to illnesses caused by Listeria or Salmonella.

Novel food vehicles associated with certain Salmonella infections included pine nuts imported from Turkey, chia seed powder imported from Canada, and moringa leaf powder in a powdered shake mix imported from South Africa. An outbreak of STEC serogroups 0126 and 0121 that impacted 56 individuals in 24 states was associated with raw wheat flour produced in the U.S. A multi-state outbreak of listeriosis attributed to caramel apples was associated with a case fatality rate of 20 percent.
Outbreak illnesses were most commonly associated with food consumption at sit-down restaurants, followed by catering or banquet facilities, institutions (e.g., schools) and occasionally, private homes. Illnesses that occurred in institutional settings were more likely to affect a larger number of individuals (average, 46.5) compared to restaurant settings (average, 11.6). 

A specific food product could be identified in less than one-half of outbreak cases; fish, dairy, chicken, pork and seeded vegetables were most commonly implicated and overall, Salmonella was the most common pathogen. The largest outbreak reported from multiple states was related to shell eggs (Salmonella serotype Enteriditis) and the second highest was related to cucumbers (Salmonella poona). 

A fraction of outbreaks were related to ingestion of fish. There were 519 distinct outbreak-associated illnesses reported with 41 hospitalizations related to scombroid or ciguatoxin poisoning syndromes. Characterized by a histamine reaction that occurs minutes to hours after eating, scombroid poisoning occurs when fish is not appropriately stored and is associated most commonly with ingestion of tuna, amberjack, mahi-mahi, blue fish and skipfish. Ciguatera poisoning, especially following eating barracuda, is characterized by the occurrence of cardiovascular, gastrointestinal and neurologic symptoms, three to 30 hours after ingestion, and accounted for nearly all of the hospitalizations related to fish ingestions. The marine toxins that are associated with seafood poisonings are unaffected by cooking and there are no routine diagnostic tests to implicate affected fish. Treatment is supportive.

Individuals can access restaurant inspection scores, which will describe conditions found in food service establishments. In Kansas City, Mo., inspection scores can be accessed for specific restaurants ( and in Kansas, at


1. Preliminary Incidence and Trends of Infections with Pathogens Transmitted Commonly Through Food, Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 2006-2017. Marder, MPH EP, Griffin PM, Cieslak PR, et al. MMWR Morb Mortal Wkly Rep 2018;67:324–328.
2. Surveillance for Foodborne Disease Outbreaks, United States, 2009-2015. Dewey-Mattia D, Manikonda K, Hall AJ, Wise ME, Crowe SJ. MMWR Surveill Summ 2018;67(No. SS-10):1–11.