There are two places where romaine lettuce comes from in the United States: Arizona and California. Marguerite Pappaioanou, an affiliate professor of environmental and occupational health sciences at the University of Washington School of Public Health, recently served as the CDC’s liaison to the FDA for food safety. Pappaioanou is an epidemiologist who now lectures on food outbreaks. She says unless you know for sure the romaine lettuce did not come from Arizona, throw it out.