longifolia) is a variety of lettuce that grows in a tall head of sturdy dark green leaves with firm ribs down their centers.

[10][11] The thick ribs, especially on the older outer leaves, have a milky fluid that gives the romaine its typically bitter herb taste.

[12] 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.

[13] 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.

[17][18] In June 2018, the Food and Drug Administration (FDA) traced the source of the latest E. coli outbreak to water from a canal located in Yuma, Arizona.

[10] Many US growers of romaine lettuce farm in Salinas, California, in the summer and the Imperial Valley and Yuma, Arizona, in the winter, relying on day laborers crossing the border from Mexico.

[24] Much of the romaine lettuce sold in northern Europe is grown in southern Spain, relying on migrant laborers from Africa.