Pending External Review Key Facts
- Iceberg lettuce, also known as crisphead, has long been a popular type of lettuce sold in the United States. It is characterized by a tight head of crisp, light green leaves.
- A crispy texture and neutral taste has made iceberg lettuce a popular addition to salad mixes, as it counterbalances the bitterness of many other types of lettuces.
- The main varieties of iceberg lettuce grown in the U.S. are Crispino, Great Lakes, Keeper, Ithaca, Maverick, and Raider.
- As a raw agricultural product with high moisture content and surface area, lettuce is susceptible to contamination. These growth characteristics are part of the reason that the Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA) have classified leafy greens, which includes iceberg lettuce, as one of the top ten riskiest foods in production.
- Production of iceberg lettuce in the United States occurs largely in California and Arizona where the mild climate contributes to high crop yields.
- Between 2000 and 2020, at least 31 iceberg lettuce-associated outbreaks were reported to CDC’s National Outbreak Reporting System (NORS), causing 1,093 illnesses, 65 hospitalizations, and no deaths.
- One of the most recent iceberg lettuce-related recalls occured in 2020 due to a multistate Cyclosporiasis outbreak associated with bagged salad mixes that contain iceberg lettuce, carrots, and red cabbage.
- The major pathogens that have caused outbreaks associated with lettuce have been Shiga-toxin producing Escherichia coli, Listeria monocytogenes, and Salmonella spp.
- For video instruction on how to wash iceberg lettuce, please visit Food Smart Colorado.
Pending External Review Content
Iceberg lettuce, also known as crisphead, is one of the six types of lettuce crops, which includes Romaine, loose-leaf, and butterhead, and it is one of the only types not available in a red varietal. These L. sativa cultivars are all within Lactuca genus, which includes most other varieties of lettuce. Because it is made up of about 95% water, crisphead lettuce nutritional content ranks the lowest among all lettuce types. However, iceberg’s crisp quality and mild flavor makes it a good addition to salad blends containing other leafy greens with higher nutrient values.
Crisphead lettuce was shipped in ice-filled containers as early as the 1900s and was given the name “iceberg” as a result of that process. It was developed to withstand the long journeys along the Trans-Atlantic Railroad and was a symbol of the expanding U.S. industrial agriculture system during the mid-20th century. Whole head iceberg is now shipped globally and has a shelf life of three to four weeks (cut lettuce has a shorter shelf life). Although iceberg can be traced to the early 20th century in the Americas, lettuce was found growing as a weed over 4,500 years ago in the Mediterranean region. Today’s cultivated lettuce is similar to the wild lettuce variety, L. scariola, from which it likely originated, and it can now be found throughout the world. Lettuce originally traveled to North America with early settlers bound for the New World, making it one of the oldest crops grown and cultivated in the United States. In the U.S. today, iceberg lettuce is grown as a cool-season crop that does particularly well in the desert climates of the Southwest during the winter months and along the central coastal regions of California during the rest of the year. It is an essential cash crop for these states and is either sold in head form or processed into salad mixes. Until recently, iceberg lettuce was the most popular variety of lettuce sold in the U.S.; however, demand for romaine and loose-leaf lettuce has now surpassed that of iceberg. Because this leafy green is a fresh, raw commodity, it is highly susceptible to contamination by foodborne pathogens and, therefore, remains at the top of the list of foodborne illness culprits. Iceberg lettuce, along with other varieties of lettuce used in salads, have caused about 22% or one-fifth of foodborne illnesses over the past decade.
Foodborne Outbreaks and Recalls
Lettuce has been associated with a number of outbreaks and is linked to Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella. In some cases, outbreaks have been traced to lettuce, but a specific type was not identified. Between 2000 and 2020, at least 31 iceberg lettuce-associated outbreaks were reported to CDC’s National Outbreak Reporting System (NORS), causing 1,093 illnesses, 65 hospitalizations, and no deaths.
A recall was administered in 2011 after Kroger grocery stores found lettuce products sold by the brand Growers Express had been contaminated with Salmonella. The CEO of Growers Express confirmed Salmonella had been found in a field in Arizona adjacent to the company’s acreage and alerted retailers that a recall should be issued. However, the recall was more precautionary because no evidence of contamination was found with the company’s lettuce.
A second recall issued in 2011 was linked to the pathogen, Listeria. Giant Eagle, a Pittsburgh-based grocery chain, identified a potential contamination and immediately removed bagged salads from their shelves. The company’s quick response helped avert an outbreak and no illness were reported. Giant Eagle also recalled shredded iceberg lettuce bags produced by River Ranch Fresh Foods after they tested positive for Listeria. The lettuce had been used in some premade deli sandwiches and customers were alerted about the concern. No illnesses were reported in connection with the recall.
In 2012, a multi-state outbreak of the Shiga toxin-producing pathogen of E. coli O157:H7, also called STEC, was associated with prepackaged leafy green mixes supplied by the company State Garden, based in Chelsea, Massachusetts. The outbreak caused 33 people in five states to become ill, with ages of those affected ranging from 4 to 66 years old. Connecticut, Massachusetts, New York, Pennsylvania, and Virginia were involved in the outbreak. Based on the available information, 46% of those who fell ill were hospitalized and two people developed hemolytic uremic syndrome (HUS), a type of kidney failure, but no deaths were reported. Multiple product brands were associated with the outbreak which involved a variety of leafy green produce, including iceberg lettuce. The particular lettuce responsible for the outbreak was not identified; however, in an effort to prevent more illness, a number of the prepackaged mixes supplied by State Garden were recalled.
Another outbreak occurred later in 2012 in Ontario, Canada, linked to the pathogen E. coli O157:H7, The outbreak was reported to have caused 30 illnesses. The likely contaminated product was associated with Fresh Point Inc. and primarily affected fast-food restaurants which use iceberg lettuce. The Canadian Food Inspection Agency worked with the company to recall the food products.
The E. coli O157:H7 pathogen caused an outbreak in 2013, which infected 33 people in four U.S. states. Those who became ill ranged in age from 2 to 78 years old. The investigation found ready-to-eat salads sold at Trader Joe’s grocery locations were to blame for the outbreak. About 32% of those who fell ill during the outbreak were hospitalized and two contracted hemolytic uremic syndrome (HUS), but no deaths were reported.
In 2015, the CDC and the FDA conducted an investigation which linked salad greens containing iceberg lettuce sold by Dole Food Company’s processing facility in Ohio with the foodborne pathogen, Listeria. Routine product sampling by the Ohio Department of Agriculture isolated Listeria monocytogenes as the pathogen in the Dole brand Field Greens packaged salads. Upon reporting this finding, Dole ceased production of the packaged salads at the processing facility in Springfield, Ohio and followed with a recall on all packaged salads produced at the facility. The multi-state outbreak infected 19 people in nine states and resulted in one death. Those affected ranged in age from 3 to 83 years old and 74% were female.
A multistate cyclosporiasis outbreak in 2020 was associated with bagged salad mixes that contain iceberg lettuce, carrots, and red cabbage. Cyclospora is a parasite that infects that gastrointestinal tract, commonly leading to diarrhea as well as other symptoms including loss of appetite, stomach cramps, weight loss, nausea, and vomiting. Most outbreaks of Cyclospora in the United States have been associated with fresh produce, where treatment of the infection requires a combination antibiotic. A total of 701 cases were reported across 14 states, leading to 38 hospitalizations and no reported deaths. Epidemiologic evidence and product traceback identified bagged lettuce mixes was the probable source of the outbreak, indicating that the contaminated products originated from the Fresh Express production facility in Streamwood, Illinois. Further traceback initially implicated multiple farms; later water sampling at a regional water management canal in Port St. Lucie, Florida tested positive for Cyclospora. While this location has been identified as a possible source of contamination, genetic testing methodologies are not available to positively match the parasite in the outbreak and sampled at the canal. In response to the outbreak, Fresh Express and private label brand salad products issued recalls of bagged salad mixes. Several store branded salad mixes were also recalled, including ALDI Little Salad Bar, Giant Eagle, Hy-Vee, Jewel-Osco Signature Farms, ShopRite Wholesome Pantry, and Walmart Marketside.
Iceberg lettuce is one of the most popular types of lettuce produced in the United States, and its superior shipping quality has enabled it to be a top seller for producers. The average U.S. price for head lettuce in the 2016 season was $27.70 per hundred weight and the estimated gross value per acre was $10,400 with production costs varying upon location. In recent years, other varieties of lettuce, such as loose leaf and Romaine, have seen a substantial increase in demand and have begun to surpass iceberg in popularity. The latest agriculture census indicated 830 farms harvested head lettuce, mostly iceberg, from 166,800 acres spanning 42 states, the majority located in California and Arizona.
Iceberg lettuce is grown year-round in California and Arizona and is shipped throughout the United States and Canada where it makes its way, in various forms, to grocery stores, restaurants, and food service establishments. Growing lettuce can be a labor-intensive process because of the delicacy of handling the product. However, the overall cost of production varies in terms of labor costs, soil, weather, water costs, and other inputs. For producers, benefits outweigh the production cost because high demand for this lettuce in the U.S. fuels profits. The consumption of all lettuce types has grown since the 1960’s, reaching a high of 34.5 pounds per capita as of 2004, which has since decreased to the 2015 annual consumption of 25.6 pounds per capita. In 2018, lettuce ranked number six in California commodity values, generating sales of 1.8 billion dollars, and it was the number 15 commodity with $297 million in sales, down 6.3% from the previous year.
The silt loam and sandy soils of the southern deserts make some regions in this area prime locations for cultivating iceberg lettuce. The loose, fertile soils with the addition of organic matter, produces well-drained, moist soil with a slightly acidic pH of 6.0 to 6.5, which aids the growth of lettuce. The time from planting to harvest is about 70 to 80 days in midsummer and up to 130 days in the fall/winter season. Seeds are planted with a precision planter and plants are subsequently spaced approximately 10 to 12 inches apart to promote optimal growth and development. The bulk of production spans from April through October in the Salinas Valley of California and from November through March in the areas of Yuma, Arizona and in the Imperial Valley of California. Ideal growing temperatures are moderate day temperatures of 73 °F and cool nighttime temperatures of 45 °F.
Generally, a head lettuce crop like iceberg needs about 38 to 50 inches of water for optimal growth, but this will vary depending on the location, soil type and equipment used in production. It is important to moisten the soil to soften it prior to planting. A large majority of the iceberg lettuce farms operating in the southern desert regions of the United States use overhead sprinklers to ensure adequate water to generate rapid growth from the seedlings. Once seedlings are established, plants are irrigated by furrows for the remainder of the growing season. Oversaturating seedlings in early growth stages can cause the plant to rot. The most effective irrigation method for growing lettuce in the central coast is to use a drip line placed at the surface, which allows water to be dispersed evenly to the plant. In terms of Good Agricultural Practices, drip irrigation is preferred to overhead sprinklers to minimize water contact with the lettuce.
The time from planting to harvest is about 70 to 80 days in midsummer and up to 130 days in the fall/winter season. Seeds are planted with a precision planter and plants are subsequently spaced approximately 10 to 12 inches apart to promote optimal growth and development. The bulk of production spans from April through October in the Salinas Valley.
The United States Department of Agriculture (USDA) has established grades and standards for the sale of all fresh produce in the U.S. based on inspection criteria specific to the quality of the product being sold. The standard grade for iceberg lettuce is U.S. No. 1. This grading requires the head to be green. If the butts or cores have been removed from the head lettuce, it is not graded by inspectors. Instead, if inspected, it is labeled “No established U.S. grade” (NOG).
Please find more information on Iceberg lettuce production on the Produce Point of Origin Database.
Due to its susceptibility to pathogens during all phases of production, iceberg lettuce, like most lettuce varieties, raises many food safety concerns. Lettuce is commonly associated with foodborne illness because there is minimal processing of the raw, leafy greens. Contamination can occur in the field (due to the plant’s proximity to the ground), during harvesting, or during transport. Although raw lettuce products are often refrigerated to maintain produce quality, refrigeration is not a food safety requirement, which can present problems.
Salad greens have been linked to 97 confirmed outbreaks; the associated pathogens include STEC (Shiga toxin-producing Escherichia coli), Norovirus, Listeria, and Salmonella, all with a similar etiology. Because minimally processed fresh-cut vegetables like lettuce are a good substrate for pathogenic microorganisms, contamination can occur both before and after harvesting of the product. From 2006 to 2012, food outbreaks have repeatedly been linked to iceberg lettuce and the pathogen E. coli O157:H7, and have resulted in 300 reported cases of illness and at least nine outbreaks. The FDA has identified agricultural water, biological soil amendments like manure, domesticated and wild animals, worker health and hygiene, and the sanitation of harvesting equipment, tools, and buildings all as potential points of contamination for leafy greens like lettuce. Contamination at the processing level can happen during washing, cutting, and storage where pathogens like pathogenic E. coli and Salmonella can be taken in through the plant tissue or can attach to cut surfaces. Plant tissue penetration may be caused by mechanical or enzymatic damage after postharvest, which may enhance the growth of pathogens on produce. The best means for combating bacteria and pathogens in lettuce production is by adopting Good Agricultural Practices from the start of production.
Recently, the lettuce industry has been working to improve pre- and post-harvest food safety. Following a 2006 spinach outbreak, the California Leafy Greens Marketing Agreement (LGMA) was established in an effort to codify industry food safety standards to help mitigate contamination and prevent future outbreaks. The LGMA is a voluntary agreement but, once adopted, participating businesses must meet the minimum food safety requirements specified and may be subject to third party audits to ensure compliance. In addition to the LGMA, the federally regulated Food Safety Modernization Act was signed into law in 2011. These new product safety agreements and regulations have compelled food industry buyers to adopt a food safety culture as the new standard for conducting business. Adding to these changes in food safety culture, the FDA released the 2020 Leafy Greens STEC Action Plan to take further steps to implement the FSMA Produce Safety Rule and expand areas of response and knowledge of environmental pathogens.
Advancements in food safety have been translated to the marketing of lettuce as well. A consumer may see lettuce labeled “washed,” “triple-washed,” or “ready-to-eat,” all of which indicate the product does not need any further washing. If the product has one of these labels, consumers are advised not to wash the lettuce further because there is a greater risk of cross contamination. On the other hand, if the lettuce product does not include a label indicating it has been prewashed, safe food handling practices should be followed by the consumer. When preparing iceberg lettuce, the core should be removed on a clean cutting board and the head should be held upside down under running water. The head should then be dried in a colander or with clean paper towels. Salad spinners can be good options for washing leafy greens and removing water. Established recommendations suggest waiting to wash lettuce until just prior to preparing it for consumption. It is also important to store all leafy greens in the refrigerator as soon as possible and to keep them separate from raw meat in order to prevent cross contamination.
As previously mentioned, iceberg or crisphead lettuce has historically been one of the most popular lettuce types consumed in the United States. Iceberg lettuce is not the most nutritious variety; however, it is well-liked because of its crunchy, crisp texture, and mild flavor. One-fourth of iceberg lettuce produced can be found in prepackaged salad mixes. About 98% of the lettuce consumed is grown domestically here in the United States. It is sold as head lettuce or in salad mixes and is generally eaten uncooked. The annual consumption of all lettuce varieties was 25.6 pounds per person in 2015 with 55% attributed to head lettuce. Lettuce production is quite profitable in the United States and, as the industry continues to grow, it is advised to adhere to food safety protocols to continue to protect consumers domestically and abroad.
Leafy vegetables are sources of various bioactive compounds because, in addition to being principal photosynthetic sites, leaves are accrual areas for various phytochemicals with antioxidant, antimicrobial, and other defensive properties. In general, iceberg lettuce lacks the kind of nutritional value often found in other types of leafy greens, such as spinach and kale, and it is slightly lower in nutritional value compared to loose-leaf and Romaine lettuce. Lettuce provides about 7 calories per one cup serving, making it good choice to satisfy hunger without added calories. In addition, lettuce is not generally a stand-alone vegetable but is often paired in salads with fruits, vegetables, nuts, and other toppings.
- Akbas, M.y. Ö H. Inactivation of Escherichia coli and Listeria monocytogenes on iceberg lettuce by dip wash treatments with organic acids. Letters in Applied Microbiology. 2007 Jun 1;44(6):619–24.
- Boriss, Hayley B Henrich. Commodity profile: Lettuce. University of California [Internet]. 2005 [cited 2017 Aug 30]; Available from: https://col.st/2wfSa
- Davidson, Gordon R. B Annemarie L, Ryser, Elliot T. Efficacy of Commercial Produce Sanitizers against Nontoxigenic Escherichia coli O157:H7 during Processing of Iceberg Lettuce in a Pilot-Scale Leafy Green Processing Line. Journal of Food Protection. 2013 Nov;76(11):1838–45.
- Gorny, James R. G Hank, Gombas, David M Kathy. Commodity Specific Food Safety Guidelines for the Lettuce and Leafy Greens Supply Chains| Food and Drug Administration [Internet]. Available from: https://col.st/trMY8
- Herman, K. M. H AJ, Gould, L. H. Outbreaks attributed to fresh leafy vegetables, United States, 1973–2012. Epidemiol Infect. 2015 Oct;143(14):3011–21.
- Lucier, Gary J Alberto. Vegetables and Melons Outlook| Electronic Outlook Report from the Economic Research Service| United States Department of Agriculture [Internet]. 2006. Available from: https://col.st/xjwrY
- McEvoy, James L. L Yaguang, Conway, William Z Bin, Feng, Hao. Potential of Escherichia coli O157:H7 to grow on field-cored lettuce as impacted by postharvest storage time and temperature. International Journal of Food Microbiology. 2009 Jan;128(3):506–9.
- Mishra, Abhinav G Miao, Buchanan, Robert L. S Donald W, Pradhan, Abani K. Prediction of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes Growth in Leafy Greens without Temperature Control. Journal of Food Protection. 2017 Jan;80(1):68–73.
- Turini, Thomas C Michael, Cantwell, Marita J Louise, Koike, Steve N Eric, Smith, Richard S Krishna, Takele, Etaferahu. Iceberg Lettuce Production in California| Vegetable Production Series| University of California| Agriculture and Natural Resources [Internet]. Available from: https://col.st/ljJjQ
- Lettuce: Shipping Point and Market Inspection Instructions| United States Department of Agriculture [Internet]. 2004. Available from: https://col.st/zpama
- Listeria Test Causes Iceberg Lettuce Recall [Internet]. Food Safety News. 2011. Available from: https://col.st/wk88O
- Canadian Taco Bell and KFC Lettuce E. coli Outbreak Over [Internet]. Food Poison Journal. 2013. Available from: https://col.st/hKaAt
- Canadian E. coli Outbreak Nears 30 [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/kNobg
- Centers for Disease Control and Prevention. Cyclosporiasis Outbreak Investigations — United States, 2020 [Internet]. Parasites. 2020 [cited 2021 Jul 14]. Available from: https://col.st/P5SIZ
- Food and Drug Administration. Fresh Express Issues a Precautionary Recall of Products Containing Iceberg, Red Cabbage and Carrots Produced at its Streamwood, IL Facility Due to a Potential Cyclospora Risk [Internet]. U.S. Food and Drug Administration. FDA; 2020 [cited 2021 Jul 14]. Available from: https://col.st/DL1Qx
- Commodity Fact Sheet: Lettuce| California Foundation for Agriculture in the Classroom [Internet]. Available from: https://col.st/WjKSI
- Grades and Standards | Agricultural Marketing Service [Internet]. [cited 2017 Aug 1]. Available from: https://col.st/evmVk
- Growing the Asteraceae (Lettuce) Family | Snohomish County | Washington State University [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/oIs5U
- Guidelines for Head Lettuce Production in Arizona (ACIS) [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/o750W
- Harvest of the Month: Salad Greens| Champions for Change| Network for a Healthy California [Internet]. Available from: https://col.st/P7Au2
- HGIC 3518 Safe Handling of Lettuce & Leafy Green Salads : Extension : Clemson University : South Carolina [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/NA1Zf
- Iceberg Lettuce | Produce Market Guide [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/hpmAP
- Iceberg Lettuce Information, Recipes and Facts [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/EYkQR
- Know your commodity guide: Lettuce| Produce Bluebook [Internet]. Available from: https://col.st/cHl4f
- Leafy Greens | EatFresh [Internet]. [cited 2017 Jul 27]. Available from: http://eatfresh.org/discover-foods/leafy-greens
- Lettuce | Agricultural Marketing Resource Center [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/PXnOm
- Lettuce| Cooperative Extension Service| University of the District of Columbia| Center for Nutrition Diet and Health [Internet]. Available from: https://col.st/YKiuV
- More Lettuce Recalled Due to Listeria [Internet]. Food Safety News. [cited 2011 Oct 14]. Available from: https://col.st/bZCK9
- Multistate Outbreak of Listeriosis Linked to Packaged Salads Produced at Springfield, Ohio Dole Processing Facility | Listeria | CDC [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/IPNm2
- Multistate Outbreak of Shiga Toxin-producing Escherichia coli O157:H7 Infections Linked to Organic Spinach and Spring Mix Blend (Final Update) | Multistate Outbreak Linked to Organic Spinach and Spring Mix Blend | E. coli | CDC [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/Pol4D
- Outbreak of STEC O157:H7 Infections linked to Ready-to-Eat Salads | E. coli | CDC [Internet]. Available from: https://col.st/PZ52K
- Promoting Lettuce : Cafeteria [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/PrlUM
- Salmonella Concerns Prompt Iceberg Lettuce Recall | Food Safety News [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/giakE
- Two Sides of the Coin for Food Safety of Cut Leafy Greens | Food Safety News [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/gG3yk
- Universal Boon to the Salad Bowl [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/OiUPE
- USDA ERS – The California Leafy Greens Industry Provides an Example of an Established Food Safety System [Internet]. [cited 2017 Jul 27]. Available from: https://col.st/krJIe