Even though the outbreak strain was identified in lettuce, federal officials continued to say today that the source of an E. Coli O157:H7 outbreak is unknown. The CDC declared the outbreak is over.

“Laboratory testing identified the outbreak strain in a sample of Tanimura & Antle romaine lettuce in a single-head package, which was on Nov. 6, 2020,” according to an outbreak updat posted today by the Centers for Disease Control and Prevention. “However, investigators were unable to determine if any ill people in this outbreak got sick from eating the recalled product. No one specifically reported eating Tanimura & Antle romaine lettuce, and some people got sick before the ‘packed on’ dates for the recalled products.

“FDA (the Food and Drug Administration) conducted traceback investigations and worked with state partners to conduct inspections at several farms. However, none of the findings identified a common source in the distribution chain or linked the farms to the outbreak.”

The CDC, public health and regulatory officials in several states, and the U.S. FDA have been investigating at least three multistate outbreaks of E. coli O157:H7 infections with as yet unknown causes. This outbreak is different from two other E. coli O157:H7 outbreaks that occurred at the same time, according to the CDC update.

As of Dec. 16, a total of 18 people infected with the outbreak strain of E. coli O157:H7 had been reported from nine states, the CDC reported today. Illnesses started on dates ranging from Sept. 2 to Nov. 6, 2020. Ill people ranged in age from 8 to 71 years, with a median age of 28 years, and 72 percent were female. Of 16 ill people with information available, six were hospitalized. No deaths were reported.

State and local public health officials interviewed ill people to determine what they ate and other exposures in the week before they got sick. Of the 13 people interviewed, all reported eating or maybe eating various types of leafy greens, including romaine lettuce eaten by nine, spinach nine, and iceberg lettuce eaten by seven of the patients.

“This outbreak ended before enough information was available for investigators to identify the likely source,” according to the CDC update.