The FDA today reported it did not find any troublesome E. coli or Salmonella strains in samples of romaine collected for a special investigation program, but the agency cautioned that the samples represent a “relatively small” portion of romaine lettuce grown in certain areas.

“The findings of this assignment suggest that microbial contamination – to the extent that it may have been present – was not widespread at the 137 FDA-registered facilities and farms wher agency investigators collected samples during the period of this field activity,” according to the report about the testing conducted by the Food and Drug Administration in 2019 and 2020. 

“The FDA cautions against making any further inferences based solely on this assignment’s findings given that the sample size was relatively small and in view of the fact that multiple foodborne illness outbreaks linked to romaine lettuce have occurred in recent years.”

None of the samples were collected directly from growing fields and the agency did not test any freshcut romaine, such as bagged salads, which has been linked to several outbreaks. The FDA found a strain of E. coli in one sample, but it determined the strain was not likely dangerous to humans.

Although the results of the sample testing did not find dangerous Salmonella or E. coli, the FDA said those results did not negate the fact that microbial hazards have repeatedly been “linked to foodborne illnesses associated with romaine lettuce consumption.” 

The FDA began the testing “assignment” in November 2019, following multiple outbreaks linked to romaine lettuce. 

The United States experienced two multistate outbreaks of E. coli O157:H7 infections in 2018 in the spring and fall, and four outbreaks of E. coli O157:H7 infections in 2019, one in the summer, and three in the fall, all linked to or possibly linked to the consumption of romaine lettuce. 

In the fall of 2020, the FDA investigated a multistate illness outbreak linked to leafy greens and caused by a strain of E. coli genetically related to a strain associated with the 2019 fall romaine lettuce outbreaks. 

Some Salmonella strains also commonly cause foodborne illness outbreaks associated with fresh produce consumption in the United States, and in 2013 the nation experienced a multistate outbreak of Salmonella Newport infections linked to romaine lettuce consumption.

The agency tested romaine specifically from sources that have been linked to outbreaks

FDA investigators collected samples from wholesalers, distribution centers, on-farm holding locations, and commercial cooling and cold storage facilities, and to a lesser extent, from refrigerated storage, prior to consumer access at grocery stores. The report did not indicate wher the E. coli positive sample was collected.

“The FDA’s goal in conducting this assignment was to see whether the target pathogens may be present at the FDA-registered facilities and farms linked by FDA traceback investigations to foodborne illness outbreaks of recent years wher romaine lettuce was confirmed or suspected to be the food vehicle,” the agency reported today.

The samples came from facilities in the Yuma, AZ, and Salinas Valley, CA, growing regions. Agency staff collected all samples in their natural form, except the outer leaves were removed. Outer leaves are not necessarily removed before holding, packing, processing or shipping.

“The agency prioritized sample collection at FDA-registered facilities and farms identified in traceback investigations as possible suppliers of romaine lettuce linked to outbreaks of foodborne illnesses from 2017 to 2019,” says the report.

The FDA has launched two longitudinal studies based in the lettuce growing regions of Arizona and California to better understand how human pathogens survive and migrate through the environment in those regions, according to the report. 

The multi-year studies are planned to involve the collection and testing of environmental samples, including adjacent land, well and surface waters, and soil inputs that may contain compost, dust and animal fecal material.