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 historically been the subject of product warnings by both U.S. and Canadian health authorities warning that consumer supplies can become adulterated 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 etymologyEdit
In British English, it is commonly known as “cos” lettuce, and in North America 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 in Italian it is called lattuga romana and in French laitue romaine, both meaning “Roman lettuce”. Hence the name “romaine”, the common term in North American English.
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 issuesEdit
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.
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Cos lettuces are probably not named for the island of Kos but for the Arabic word for lettuce
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- The dictionary definition of romaine at Wiktionary