Scott Gottlieb, commissioner of the United States Food and Drug Administration, tweeted over the weekend that the romaine lettuce tainted with E. coli likely came from California.
If so, it would restore markets for romaine from other parts of the United States.
The Centers for Disease Control in the U.S. and the Public Health Agency of Canada have been advising people to dump romaine because of the risk of contamination.
More than 20 Canadians have been sickened enough to require hospitalization.
