A romaine lettuce field is visible in 2016 near San Luis, Ariz. At least 53 people have been sickened by tainted, chopped romaine lettuce in an expanding E. coli outbreak that now spans 16 states, the Centers for Disease Control and Prevention said on April 18. The contaminated greens have been traced to Yuma, Ariz., but investigators recommended abundant caution because they have not yet identified a specific source. (Caitlin OHara/The New York Times) Photo: CAITLIN O'HARA, STR / NYT / NYTNS
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