An investigation has linked the Escherichia coli outbreak in romaine lettuce that has sickened 59 people in 15 states to a contaminated water reservoir at a farm in Santa Barbara County in California. Whole genome sequencing linked the strain in the sediment of the reservoir at Adam Brothers farm in Santa Maria to strains of the bacterium found in some of the cases. Health officials warn some people may have become sick from other contaminated farms, and romaine lettuce from two other California counties, San Benito and Monterey, has been linked to the outbreak, as reported by CBS News in San Francisco, California. A teleconference today held by officials from the U.S. Centers for Disease Control and Prevention and the U.S. Food and Drug Administration could not explain why this particular strain of E. coli has only been tied to romaine, which is especially puzzling given that the farm with the contaminated reservoir also grows other lettuce varieties. The agencies emphasized that many other questions remain about the origin of this outbreak and the investigation is continuing. A nationwide ban on all romaine lettuce was announced on 20 November, but producers have begun to label packages to indicate where it was grown, and the only remaining concerns are about romaine from the three counties that have been tied to disease. The first case surfaced on 5 October and the last one on 11 November.