Romaine or cos lettuce (Lactuca sativa L. var. longifolia) is a variety of lettuce that grows in a tall head of sturdy dark green leaves with firm ribs down their centers. Unlike most lettuces, it is tolerant of heat. In North America, romaine is sold as whole heads or as “hearts” that have had the outer leaves removed and are often packaged together.
Commercially sold romaine lettuce has occasionally been the subject of product warnings by both U.S. and Canadian health authorities warning that consumer supplies can become contaminated with or host pathogenic E. coli bacteria. Cattle can harbor the bacteria without ill effects, and be asymptomatic carriers of the bacterium. Lettuce becomes contaminated with the bacterium as the result of cattle manure being used to fertilize crop fields, or the proximity of cattle pastures and feedlots to water sources used to irrigate crops. 
Origin and etymology
In British English, it is commonly known as “cos” lettuce, and in North American English as “romaine” lettuce. Many dictionaries trace the word cos to the name of the Greek island of Cos, from which the lettuce was presumably introduced. Other authorities trace cos to the Arabic word for lettuce, khus خس [xus].
It apparently reached Western Europe via Rome, as it is called lattuga romana in Italian and laitue romaine in French, both meaning “Roman lettuce”. Hence the name “romaine”, the common term in North America.
Romaine is a common salad green, and is the usual lettuce used in Caesar salad. Romaine lettuce is commonly used in Middle Eastern cuisine. Romaine, like other lettuces, may also be cooked. For example, it can be braised or made into soup. The thick ribs, especially on the older outer leaves, should have a milky fluid that gives the romaine its typically bitter herb taste.
In North American supermarkets, romaine is widely available year-round.
|Nutritional value per 100 g (3.5 oz)|
|Energy||72 kJ (17 kcal)|
|Dietary fibre||2.1 g|
|Vitamin A equiv.|
|†Percentages are roughly approximated using US recommendations for adults. |
Source: USDA Nutrient Database
Food safety issues
From November 2017 through January 2018, the Public Health Agency of Canada (PHA) identified romaine as being linked to illness in 41 persons in Canada. A probably related outbreak affected 25 people in 15 states of the U.S. who ate leafy greens, but the U.S. Centers for Disease Control (CDC) were unable to confirm that it was romaine in particular. There was one death. The disease agent was Shiga toxin-producing E. coli O157:H7. The most recent illness started on December 12, 2017; the PHA declared the outbreak over on January 10, 2018, and the CDC declared it over on January 25.
In response to another E. coli O157:H7 outbreak, which probably began in mid-March 2018, the CDC recommended in April 2018 that consumers not buy or eat romaine lettuce unless they could confirm it was not from the Yuma, Arizona, growing region. On May 22, 2018, after a month-long warning, the CDC announced it was now safe to consume romaine again. The outbreak killed five people and caused 89 hospitalizations across 32 states.
In November 2018, the US CDC and the PHA of Canada issued a warning to consumers that romaine lettuce should not be consumed in any form, and that they should dispose of any currently on hand. The same strain of E. coli identified in the 2017-2018 outbreak was implicated. At least 43 people became ill in this outbreak, which the FDA traced to one of six counties in Central California: Monterey, San Benito, San Luis Obispo, Santa Barbara, Santa Cruz and Ventura. As of January 9, 2019, the U.S. Centers for Disease Control and Prevention (CDC) has declared the most recent Escherichia coli O157:H7 outbreak linked to California grown romaine lettuce over.
- "Escherichia coli". Retrieved June 24, 2010.
- Pruimboom-Brees IM, Morgan TW, Ackermann MR, Nystrom ED, Samuel JE, Cornick NA, Moon HW (September 2000). "Cattle lack vascular receptors for Escherichia coli O157:H7 Shiga toxins". Proceedings of the National Academy of Sciences of the United States of America. 97 (19): 10325–9. doi:10.1073/pnas.190329997. PMC 27023. PMID 10973498.
- Walker, Norman Wardhaugh (1970). Cos or Romaine Lettuce Juice. Fresh Vegetable and Fruit Juices: What's Missing in Your Body?. Book Publishing Company. ISBN 9780890190333. Retrieved 2 December 2013.
- Oxford English Dictionary, First Edition, 1893, s.v. 'cos'
- Davidson, Alan (1999). The Oxford Companion to Food. Oxford University Press. ISBN 978-0-19-211579-9.
Cos lettuces are probably not named for the island of Kos but for the Arabic word for lettuce
- Smith, K. Annabelle (16 July 2013). "When Lettuce Was a Sacred Sex Symbol". Smithsonian Museum. Retrieved 27 January 2018.
- Bradshaw, Paul; Hoffman, Lawrence (August 19, 2000). "Towards a History of the Paschal Meal". Passover and Easter: Origin and History to Modern Times. University of Notre Dame Press. ISBN 9780268038595.
- Eisenberg, Ronald L. (2010). Jewish Traditions: A JPS Guide. Jewish Publication Society. p. 286. ISBN 978-0827610392.
- Bittman, Mark (2 April 2010). "The Charms of the Loser Lettuces". New York Times. Retrieved 27 January 2018.
- Bittman, Mark (2 April 2010). "Braised Romaine Hearts". Retrieved 27 January 2018.
- "AICR's Foods That Fight Cancer: Dark Green Leafy Vegetables". American Institute for Cancer Research.
- "Public Health Notice – Outbreak of E. coli infections linked to romaine lettuce", Public Health Agency of Canada, February 9, 2018
- "Multistate Outbreak of Shiga toxin-producing Escherichia coli O157:H7 Infections Linked to Leafy Greens (Final Update)", Centers for Disease Control and Prevention, posted January 25, 2018
- "Multistate Outbreak of E. coli O157:H7 Infections Linked to Romaine Lettuce | Investigation Notice: Multistate Outbreak of E. coli O157:H7 Infections April 2018 | E. coli | CDC". www.cdc.gov. 2018-04-20. Retrieved 2018-04-21.
- Sun, Lena H. (2018-04-20). "E. coli outbreak warning expands to all types of romaine lettuce". Washington Post. ISSN 0190-8286. Retrieved 2018-04-21.
- Judkis, Maura (2018-05-22). "Our national romaine lettuce crisis is over, says the CDC. Here's how to celebrate". The Washington Post. Retrieved 2018-05-22.
- Phillips, Kristine (2018-06-02). "Five dead, nearly 200 sick in E. coli outbreak from lettuce. And investigators are stumped". The Washington Post. Retrieved 2018-06-03.
- "FDA Investigating Multistate Outbreak of E. coli O157:H7 Infections Linked to Romaine Lettuce from Yuma Growing Region". FDA. 2018-06-01. Retrieved 2018-06-03.
- Chappell, Bill (June 29, 2018). "It Was The Water, FDA Says Of Romaine E. coli Outbreak That Killed Five". NPR. Retrieved June 29, 2018.
- United States Centers for Disease Control, "Outbreak of E. coli Infections Linked to Romaine Lettuce", November 20, 2018 
- Public Health Agency of Canada, "Public Health Notice - Outbreak of E. coli infections linked to romaine lettuce", November 20, 2018 
- Eduardo Cuevas (November 30, 2018). "County a possible source of E. coli: At least 43 have been sickened in outbreak". Salinas Californian. USA Today. p. A1.
- Kate Cimini (November 30, 2018). "Border shutdown worries ag industry: Trump threats come amid E. coli outbreak tied to romaine". Salinas Californian. USA Today. p. A1.
- Tooke, William (1855). The Monarchy of France: its rise, progress, and fall. London: Sampson Low & Son. p. 634.
- The dictionary definition of romaine at Wiktionary