1. Centers for Disease Control and Prevention (CDC). Vital signs. Safer food saves lives. Accessed January 29, 2016.
  2. Centers for Disease Control and Prevention (CDC). Multistate outbreak of listeriosis linked to Blue Bell Creameries products (final update). Accessed January 29, 2016.
  3. Centers for Disease Control and Prevention (CDC). Listeria (listeriosis): definition & symptoms. Accessed January 29, 2016.
  4. Centers for Disease Control and Prevention (CDC). PulseNet. Accessed January 29, 2016.
  5. Centers for Disease Control and Prevention (CDC). Multistate outbreak of Salmonella Poona infections linked to imported cucumbers (final update). Accessed January 29, 2016.
  6. Centers for Disease Control and Prevention (CDC). Multistate outbreak of listeriosis linked to soft cheeses distributed by Karoun Dairies, Inc. (final update). Accessed January 29, 2016.
  7. Centers for Disease Control and Prevention (CDC). Multistate outbreaks of Shiga toxin-producing Escherichia coli O26 infections linked to Chipotle Mexican Grill restaurants. Accessed January 29, 2016.
  8. Centers for Disease Control and Prevention (CDC). Multistate outbreak of multidrug-resistant Salmonella I 4,[5],12:i:- and Salmonella Infantis infections linked to pork (final update). Accessed January 29, 2016.
  9. Centers for Disease Control and Prevention (CDC). Multistate outbreak of Shiga toxin-producing Escherichia coli O157:H7 infections linked to Costco rotisserie chicken salad (final update). Accessed January 29, 2016.
  10. Centers for Disease Control and Prevention (CDC). Multistate outbreak of Salmonella paratyphi B variant L(+) tartrate(+) infections linked to JEM raw brand sprouted nut butter spreads (final update). Accessed January 29, 2016.
  11. Centers for Disease Control and Prevention (CDC). The future of PulseNet. Accessed February 9, 2016.

Contributor Information

Sabah Ghulamali, MPH
Division of Foodborne, Waterborne, and Environmental Diseases
Centers for Disease and Control Prevention (CDC)
Atlanta, Georgia

Disclosure: Sabah Ghulamali, MPH, has disclosed no relevant financial relationships.

Laura Burnworth, MPH
Health Communication Specialist
Division of Foodborne, Waterborne, and Environmental Diseases
Centers for Disease and Control Prevention (CDC)
Atlanta, Georgia

Disclosure: Laura Burnworth, MPH, has disclosed no relevant financial relationships.


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An Alarming Trend: Multistate Foodborne Illness Outbreaks

Sabah Ghulamali, MPH; Laura Burnworth, MPH  |  June 28, 2016

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Slide 1

A Year of Multistate Foodborne Illness Outbreaks

Foodborne illness (sometimes referred to as "food poisoning") is a common yet preventable occurrence. The Centers for Disease Control and Prevention (CDC) estimates that each year, about 1 in 6 Americans (48 million people) gets sick from foodborne illness. An estimated 128,000 people are hospitalized and 3000 die of foodborne diseases every year.

Most foodborne outbreaks occur within just one state. Only 3% of foodborne outbreaks sicken people in multiple states, and yet these multistate outbreaks caused more than one half of all deaths reported in foodborne outbreaks in 2015 alone.[1] Foods that cause multistate outbreaks are contaminated before they reach a restaurant or home kitchen. Investigating these outbreaks often reveals problems on the farm, in processing, or in distribution that resulted in contaminated food. Several notable and complicated multistate foodborne outbreaks were investigated in 2015. These outbreaks were caused by a wide range of contaminated foods, including ice cream, raw vegetables, sprouted nut butters, and Mexican-style restaurant meals.

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Slide 2

Listeria monocytogenes and Ice Cream

From January 2010 through January 2015[2]:

  • Case count (outbreak strain of L monocytogenes): 10
  • States: 4
  • Hospitalizations: 10
  • Deaths: 3

A cluster of ill patients was identified in a Kansas hospital, and product testing revealed that the source of Listeria was a Blue Bell ice cream product served to patients. Soon after, that strain was found in a Blue Bell production facility. This complex outbreak investigation involved listeriosis cases occurring over several years. Listeriosis is a serious illness that primarily affects pregnant women and their newborns, adults older than 65 years, and people with weakened immune systems.[3] As the first multistate outbreak of listeriosis linked to ice cream, it alarmed the ice cream industry. As a result of this investigation, Blue Bell Creameries, the ice cream manufacturer, recalled all ice cream produced at its facilities and took action to improve food safety.

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Slide 3


Public health investigators used the PulseNet[4] system to identify illnesses that were part of this outbreak, piecing together data from 5 years. PulseNet includes DNA "fingerprints" using the subtyping techniques of pulsed-field gel electrophoresis (PFGE) and whole-genome sequencing (WGS). WGS gives a more detailed DNA fingerprint than PFGE and can show whether isolates from people and food production facilities are related genetically. WGS was used to confirm that cases dating back to 2010 were part of the outbreak. The US Food and Drug Administration and the National Institutes of Health collaborated with CDC in using this new technology.

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Slide 4

Salmonella Poona and Cucumbers

From July 2015 through February 2016[5]:

  • Case count (outbreak strains of Salmonella Poona): 907
  • States: 40
  • Hospitalizations: 204
  • Deaths: 6

Epidemiologic, laboratory, and traceback investigations identified imported cucumbers as a likely source of the outbreak, and two cucumber recalls took place. After peaking, the number of reported illnesses declined substantially, but not as fast as expected. An investigation was unable to determine whether the higher-than-expected rate of illness could be explained by cross-contamination by recalled cucumbers in shipping containers or at retail locations.

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Slide 5

Listeria monocytogenes and Soft Cheeses

From June 2010 to October 2015[6]:

  • Case count (outbreak strains of L monocytogenes): 30
  • States: 10
  • Hospitalizations: 28
  • Deaths: 3

This outbreak (the second largest outbreak of listeriosis since that linked to cantaloupe in 2011) was not easy to solve. Several pieces of evidence were critical to the investigation. First, 67% of ill people were of Middle Eastern or Eastern European descent, and this provided a clue about the foods that could be linked to the illnesses. Second, WGS of isolates from ill people showed that the cases were closely related genetically and probably had a common source of contamination. Finally, environmental testing at the Karoun Dairies cheese manufacturing facility confirmed that soft cheeses made from pasteurized milk were the source.

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Slide 6

Shiga Toxin-Producing Escherichia coli O26 and a Mexican-Style Restaurant Chain

From October 2015 to January 2016, two separate outbreaks involving different strains of E coli O26 were identified[7]:

  • Case count (outbreak strains of E coli O26): 60
  • States: 14
  • Hospitalizations: 22
  • Deaths: 0

Investigators in several states, the CDC, the US Food and Drug Administration (FDA), the US Department of Agriculture, and Chipotle Mexican Grill worked diligently to determine the source of the two outbreaks. Interviews with ill people suggested that a common meal or ingredient served at Chipotle restaurants was the likely source of the outbreaks, but food testing and a review of Chipotle's distribution records did not identify a particular food item or ingredient that could explain either outbreak. Because the contaminated food couldn't be identified, CDC recommended that people contact a healthcare provider if they became ill with diarrhea shortly after eating at a Chipotle restaurant so they could be interviewed to help guide investigators to the source of the illness.

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Slide 7

Multidrug-Resistant Salmonella I 4,[5],12:i- and Salmonella Infantis and Pork

From April 25, 2015 to September 25, 2015[8]:

  • Case count (outbreak strains of Salmonella I 4,[5],12:i- or Salmonella Infantis): 92
  • States: 5
  • Hospitalizations: 30
  • Deaths: 0

This outbreak began in Washington and was eventually linked to pork from a slaughter plant in that state. Ill people reported eating pork prepared in one of several ways. Multiple clusters of ill people said they ate at whole-pig roasts in the week before they got sick. The outbreak highlighted the need to prepare, cook, and serve whole pigs safely. Another noteworthy aspect of this outbreak was that tests indicated that the strain of Salmonella I 4,[5],12:i- causing illness was resistant to multiple drugs, including ampicillin, streptomycin, sulfisoxazole, and tetracycline. Antibiotic resistance may be associated with increased risk for hospitalization, bloodstream infection, or treatment failure.

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Slide 8

Escherichia coli O157:H7 and Chicken Salad

From October 2015 to December 2015[9]:

  • Case count (outbreak strain of with Shiga toxin–producing E coli O157:H7): 19
  • States: 7
  • Hospitalizations: 5
  • Cases of hemolytic uremic syndrome: 2
  • Deaths: 0

Soon after investigators realized that the majority of ill people reported eating Costco rotisserie chicken salad, the company removed all remaining chicken salad from its stores throughout the United States. When ingredients from the chicken salad were tested, initial results found E coli in the celery and onion blend produced by Taylor Farms Pacific, Inc. Although further laboratory analysis could not confirm the presence of E coli in the mix, Taylor Farms Pacific recalled the blend out of an abundance of caution. The FDA conducted a traceback investigation of the FDA-regulated ingredients used in the chicken salad but could not identify a common source of contamination. No additional illnesses were reported after the actions taken by Costco and Taylor Farms.

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Slide 9

Salmonella Paratyphi B Variant L(+) Tartrate(+) and Sprouted Nut Butters

From July 28, 2015 to November 22, 2015[10]:

  • Case count (outbreak strain of Salmonella Paratyphi B variant L[+] tartrate[+]): 13
  • States: 10
  • Hospitalizations: 0
  • Deaths: 0

Nut butters have caused multistate foodborne outbreaks over the past several years. In this outbreak, the epidemiologic data indicated that Jem Raw brand sprouted nut butter spreads were linked to illness. According to the manufacturer, the nuts used in their spreads were soaked and sprouted for 24 hours, after which they were dehydrated before being ground and blended into the nut butter spreads. Raw sprouts are a known source of foodborne illness. The fact that the nuts were sprouted before grinding into nut butter may have increased the likelihood that any bacteria present on the raw nuts were able to multiply.

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Slide 10

Emerging Issues: Testing

New diagnostic tests called "culture-independent diagnostic testing" (CIDT) can identify the bacteria that made a person sick without using traditional, standard microbiologic techniques. Standard tests take a day or more to grow the microbe in the laboratory, resulting in a pure culture of the living microbe. CIDT appeals to clinicians and patients because it provides results faster than culture-dependent techniques, and can test for bacteria, viruses, and parasites at the same time.

However, CIDT presents a challenge to public health surveillance because it does not generate the cultures needed to identify the DNA fingerprints and antibiotic resistance patterns used by public health investigators to detect and investigate foodborne outbreaks. CDC urges providers to continue to submit samples to the lab for culture confirmation even after getting a positive result from a rapid test, so CDC can continue to quickly detect and investigate foodborne outbreaks.[11]

WGS has proven to be a successful tool for investigators, enhancing the ability to detect and solve outbreaks faster, with more accuracy. WGS has been used as a highly discriminatory DNA fingerprinting technique in outbreaks of listeriosis since 2013, and will now be used for other pathogens, including Shiga toxin-producing E coli and Salmonella.

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Slide 11

Emerging Issues: Raw Food Movement

Another emerging issue is the growing popularity of unprocessed, raw foods. Multistate outbreaks of foodborne disease have been linked to various raw foods over the past several years, and CDC expects this trend to continue as people continue to choose less processed foods. People at higher risk for severe foodborne illness (young children, older adults, those with weakened immune systems) should consider the risks associated with unprocessed and raw items when choosing foods.

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