“Quality is our Recipe” – Lettuce Reconsider That Slogan

By Savanna Ledford

Wendy’s is a popular fast-food chain that promises quality and offers great late night eats to over 12 million loyal customers.1 However, in a turn of events that turned stomachs, the Centers for Disease Control and Prevention (CDC) launched an E. coli investigation after 97 people fell ill after eating sandwiches with romaine lettuce at Wendy’s located in Indiana, Michigan, Ohio, and Pennsylvania, leading to 43 hospitalizations.2 Wendy’s has removed the romaine lettuce from sandwich use while the CDC investigates lettuce as the source of the E. coli outbreak.2

What is E. coli?

Escherichia coli (E. coli), a Gram-negative rod-shaped bacterium, is found in the environment, food, and intestines of both humans and animals.3,4 Discovered in 1885 by Theodor Escherich, studies have identified over 700 serotypes of E. coli with most being harmless; however, there are strains that lead to illness, such as E. coli O157:H7.3,5 Discovered in 1982, E. coli O157:H7 causes disease due to the Shiga toxin-producing capabilities of the strain.3,4 Shiga toxin-producing E. coli (STEC) promotes disease by colonizing and multiplying pathogens in intestinal mucosal surfaces.6 The bacteria acquired virulence factors from plasmids (small DNA molecules), transposons (DNA sequence that can change positions within a genome), bacteriophages (viruses that infects bacteria), or pathogenicity islands (encode virulence factors), allowing researchers to classify the bacteria further based on pathogenicity mechanisms.3 E. coli O157:H7 has become the source of several outbreaks since its discovery, and is one of the most common foodborne pathogens.3 According to the CDC, E. coli O157:H7  has caused 73,000 illnesses, 2,200 hospitalizations, and 60 deaths each year in the United States, with an annual cost of illness adding up to 405 million dollars.3

How is E. coli transmitted?

Within the United States, the most common documented route of E. coli transmission is consumption of contaminated water or foods such as raw/undercooked meats, raw milk, or raw vegetables.3,7 There have also been documented cases where transmission occurred from person-to-person at day-care facilities.3 Other transmission routes include foodborne, waterborne, unknown, and animal contact (Figure 1).

Figure 1: Route of transmission for E. coli.3

With cattle being the natural reservoir for E. coli, contaminated beef is considered the most common vehicle for E. coli O157:H7 outbreaks.3 However, as in the Wendy’s case, lettuce can also serve as a vehicle linked to E. coli O157:H7 outbreaks,3 because of the way the lettuce is grown and consumed.8 Producing lettuce requires irrigation water, which can lead to cross-contamination due to waste from surrounding farm production facilities getting into the lettuce water source.8 If the crops are not near an animal production facility, cross-contamination can occur from birds or other animals that pass through.8 For these reasons, if contaminated lettuce makes it to grocery store shelves, failure to wash lettuce prior to consumption can lead to outbreaks since E. coli sticks to the surface and inside of the lettuce leaf.8 While you may want to run to your grocery store to purchase pre-washed lettuce thinking it will solve all your contamination woes, note that the pre-wash process only removes dirt before being cut in a processing plant, which ironically causes the lettuce to release sugar that promotes E. coli growth.8

What are the symptoms?

Let’s say you are one of the unlucky customers who consumed an E. coli-contaminated lettuce-laden sandwich at Wendy’s. Symptoms can start within three to four days of consumption but some may not feel ill until ten days after consuming the product.4 Common symptoms include stomach cramps, diarrhea, vomiting, and fever.4 Although most infected individuals exhibit only mild illness, 5 to 10% of infected people experience hemolytic uremic syndrome (HUS), a life-threatening complication.4 Symptoms of HUS include decreased urination, fatigue, and losing color in the cheeks and lower eyelids.4 If you or a loved one has diarrhea for more than three days while having a fever over 102 degrees, bloody diarrhea, or frequent vomiting, seek medical care.4

What preventative measures can you take?

People who are pregnant, newborns, children, older adults, and/or have a compromised immune system have a higher risk for foodborne illness but anyone can be exposed to E. coli O157:H7 .4 Although Wendy’s has removed the potentially contaminated lettuce from the states identified in the CDC investigation, there are other preventative steps one can take to lower their risk of infection. Preventative measures include 1) practice proper hygiene such as washing your hands thoroughly after contact with animals or preparing food, 2) cook meats thoroughly, 3) don’t cross-contaminate in food preparation areas, 4) avoid raw and unpasteurized products, and 5) don’t swallow water when swimming in lakes, pools, and streams.4

Global E. coli Outbreaks

So far in 2022, there have been two reported E. coli investigations, the Wendy’s investigation and the ground beef in select HelloFresh meal kits that were shipped between July 2 to July 21.9 During 2020 to 2021 there were eight investigations, including links as diverse as clover sprouts to cake mix.9 From 2020 to 2022, most E. coli outbreaks had few hospitalizations and recorded cases, unlike the United States 1999 outbreak that led to 781 cases with 70 hospitalizations, 15 people HUS cases, and two deaths.10 While the United States maintains low levels of E. coli outbreaks, Germany and the United Kingdom account for 47% of all global E. coli O157:H7  infections with 2,226 and 1,840 cases, respectively.11 Within 2018 alone, there were 48 E. coli O157:H7 outbreaks in Europe, with 381 cases across 10 countries.11 Compare this to 2018 in the United States which had only three outbreak investigations with a total of 290 cases.9 If you are interested in learning more about the E. coli outbreak investigations occurring within the United States, click here! More information regarding how the CDC tracks and investigates foodborne outbreaks can be found in a previous LTS article by Chris Kendra, here.


  • The CDC is investigating an E. coli outbreak at Wendy’s located in Indiana, Michigan, Ohio, and Pennsylvania.
  • E. coli outbreaks can lead to serious illness but by practicing proper food/drink hygiene, consuming pasteurized products, and drinking filtered water, outbreaks can be contained.


  1. McMahon, C (2022). 20 Wendy’s Statistics (2022): Restaurant Count, Diners, and Facts. Retrieved from https://www.zippia.com/advice/wendys-statistics/.
  2. CDC (2022). E. coli Outbreak with Unknown Food Source. Retrieved from https://www.cdc.gov/ecoli/2022/o157h7-08-22/index.html.
  3. Lim JY, Yoon J, Hovde CJ. A brief overview of Escherichia coli O157:H7 and its plasmid O157. J Microbiol Biotechnol. 2010 Jan;20(1):5-14. PMID: 20134227; PMCID: PMC3645889.
  4. CDC (2022). E. coli (Escherichia coli). Retrieved from https://www.cdc.gov/ecoli/index.html.
  5. Minnesota Department of Health (2022). Escherichia coli (E. coli). Retrieved from https://www.health.state.mn.us/diseases/ecoli/.
  6. Menge, C (2020). Molecular Biology of Escherichia coli Shiga Toxins’ Effects on Mammalian Cells. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7290813/.
  7. WHO (2022). E. coli. Retrieved from https://www.who.int/news-room/fact-sheets/detail/e-coli.
  8. Hogan, S (2018). Here’s why lettuce keeps getting contaminated with E.coli. Retrieved from https://www.cbc.ca/news/health/lettuce-e-coli-contamination-1.4913956.
  9. CDC (2022). Reports of Selected E. coli Outbreak Investigations. Retrieved from https://www.cdc.gov/ecoli/outbreaks.html.
  10. Rangel et al. (2005). Epidemiology of Escherichia coli O157:H7 Outbreaks, United States, 1982–2002. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3320345/#:~:text=The%20largest%20U.S.,and%202%20died%20(26).
  11. Whitworth, J (2020). Large E. coli increase recorded for Europe in 2018. Retrieved from https://www.foodsafetynews.com/2020/05/large-e-coli-increase-recorded-for-europe-in-2018/.

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