Outbreak Tracker
Outbreak Tracker
December 17, 2019
5 min read

Are outbreaks involving fresh produce, including romaine lettuce, on the rise?

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Kirk Smith, DVM, PhD, MS
Kirk Smith

The CDC and other public health institutions are investigating another Escherichia coli outbreak linked to leafy greens, this time Fresh Express Sunflower Crisp chopped salad kits.

As of Dec. 9, the outbreak included eight cases in three states, including three hospitalizations and no deaths.

The product has not been recalled, but the CDC urged consumers and retailers not to sell or consume any Fresh Express kits with a lot code that begins with Z and the UPC 071279309064, and a best-before date up to and including Dec. 7, 2019.

According to the CDC, the Fresh Express salad kits implicated in the outbreak contain romaine lettuce, although it is unclear if the outbreak is related to another ongoing E. coli outbreak linked to romaine lettuce from a growing region in California.

Romaine lettuce 
In the past 2 years, there have been notable outbreaks linked to romaine lettuce and leafy greens.
Source: Adobe.

Why do there seem to be so many outbreaks linked to produce these days? Laura Whitlock, communications lead for foodborne outbreaks at the CDC, called the question “complicated.”

“Foodborne outbreaks from contaminated fresh produce have been increasingly recognized in many parts of the world in recent years,” Whitlock told Healio. “This reflects a convergence of increasing consumption of fresh produce, changes in production and distribution, and a growing ability to detect the problem on the part of public health officials.”

Kirk Smith, DVM, PhD , MS, manager of the Foodborne, Vectorborne, Waterborne, and Zoonotic Diseases Unit at the Minnesota Department of Health, suggested that outbreaks are not necessarily on the rise, but that media coverage has increased awareness of them.

“Honestly, leafy greens and E. coli 0157 have been a problem going back at least to the mid-1990s,” he told Healio. “There are leafy green/E. coli 0157 outbreaks virtually every year, and usually a few to several. We really aren’t seeing more in the past 2 or 3 years than we used to. I think they are probably just getting more attention.”

Recent outbreaks

There have been several notable foodborne outbreaks linked to produce in the past two years.

An outbreak in November and December 2017 that was linked to contaminated leafy greens sickened 25 people and hospitalized nine, including two individuals who developed hemolytic uremic syndrome (HUS). One person died. Patients lived in both the United States and Canada.

A 2018 outbreak lasting about 4 months, from March to June, sickened 210 people from 36 states. The CDC reported 96 hospitalizations, including 27 individuals who developed HUS, and five deaths. There was no recall, but the infections were linked to romaine lettuce from the Yuma growing region in Arizona.


Another 2018 outbreak was linked to romaine lettuce from the Central Coastal growing regions in northern and central California. It lasted around 2 months, from October to December, and was declared officially over in January. The multistate outbreak sickened 62 and hospitalized 25, including two individuals who developed HUS. No deaths were reported, but red leaf lettuce, green leaf lettuce and cauliflower harvested between Nov. 27 and 30, 2018, from Adam Bros. Farming Inc. were recalled, as were sandwiches and other products under the Northwest Cuisine Creations and Fresh & Local labels from Spokane Produce Inc.

That outbreak prompted the CDC to recommend that consumers throw away all products containing romaine lettuce, and led to changes in how the leafy greens are packaged, with the industry agreeing to label packages with a harvest location by region.

Beginning in September 2019, an outbreak of E. coli O157:H7 infections has sickened 102 people from 23 states and hospitalized 58. There have been no deaths, but 10 people developed HUS. The outbreak was linked to romaine lettuce grown in the Salinas, California, growing region. According to the CDC, the E. coli strain implicated in that outbreak is the same strain that caused the latter outbreak linked to romaine lettuce in 2018 and the leafy green outbreak in 2017.

Reducing foodborne illness

Smith said there have been concerted efforts to “fix” or minimize foodborne outbreaks from leafy greens.

“Even going back to 2005, 2006, 2007, there were a lot of things that were tried, like implementing best growing practices and things like that,” Smith said.

Further efforts were undertaken in 2011 with the passing of the Food Safety Modernization Act.

“Produce safety was a part of that, but that’s being implemented piecemeal along the way,” Smith said. “I think, especially with last year and this year, everybody in the industry and the federal regulatory agencies will have to up their game to do something more to help with this problem, because it’s getting quite dramatic.”

Whitlock explained that contamination of leafy vegetables with E. coli or Salmonella can occur at just about any point in production. However, she noted that epidemiological data from many of the multistate outbreaks suggests that contamination occurred early in production.

“Leafy vegetables can become contaminated with pathogens by water used for irrigation, animal manure used for fertilizer, and feral animals that traverse vegetable fields,” she said. “Contamination can also occur during processing, including during washing, cutting and storage.”


Lettuce is prone to contamination because it is grown outdoors without any personal protection, like a rind or shell, Whitlock noted.

“It is concerning to us that we continue to detect outbreaks linked to leafy greens. These repeated incidences underscore why more work is needed to prevent these outbreaks from occurring, and prevent more people from getting sick,” she said.

Whitlock recommended that clinicians urge their patients not to eat or buy lettuce from the Salinas growing region. She said they should remind patients to check the packaging for the harvest region, and if there is none, do not buy or eat the product.

“We rely on interviews with ill people about foods they’ve recently consumed to gather data, help identify a possible source and prevent more people from getting sick. It can be challenging and time-consuming to reach people,” Whitlock said. “Clinicians can be very helpful in letting their patients who have been sick with E. coli know that they are likely to be contacted by their local health department and emphasize the importance of agreeing to be interviewed.”

Smith explained that the symptom profile of Shiga toxin-producing E. coli (STEC) is “distinct,” and that clinicians’ most important role during outbreaks is to manage patients appropriately.

“Recognize potential patients, test them appropriately and treat them appropriately,” he said. “Of course, with STEC, E. coli 0157 and other serogroups that produce Shiga toxin 2 — which is one of two Shiga toxin types — [patients] should not be treated with antimicrobials for gastroenteritis because that increases the risk of subsequent development of HUS.” – by Marley Ghizzone


CDC. Outbreak of E. coli infections linked to Fresh Express Sunflower Crisp chopped salad kits. https://www.cdc.gov/ecoli/2019/o157h7-12-19/index.html. Accessed December 13, 2019.

CDC. Outbreak of E. coli infections linked to romaine lettuce. https://www.cdc.gov/ecoli/2019/o157h7-11-19/index.html. Accessed December 13, 2019.

CDC. Multistate outbreak of Shiga toxin-producing Escherichia coli O157:H7 infections linked to leafy greens (final update). https://www.cdc.gov/ecoli/2017/o157h7-12-17/index.html. Accessed December 13, 2019.

CDC. Outbreak of E. coli infections linked to romaine lettuce. https://www.cdc.gov/ecoli/2018/o157h7-11-18/index.html. Accessed December 13, 2019.

CDC. Multistate outbreak of E. coli O157:H7 infections linked to romaine lettuce (final update). https://www.cdc.gov/ecoli/2018/o157h7-04-18/index.html. Accessed December 13, 2019.

WHO. More complex foodborne disease outbreaks require new technologies, greater transparency. https://www.who.int/news-room/detail/06-12-2019-more-complex-foodborne-disease-outbreaks-requires-new-technologies-greater-transparency. Accessed December 13, 2019.

Disclosures: Whitlock and Smith report no relevant financial disclosures.