A new report suggests cattle may have been partially to blame for the E. coli outbreaks that spread across the country last fall.
The Food and Drug Administration (FDA) has released the findings of an investigation regarding the E. coli outbreaks tied to romaine lettuce. The report suggests the proximity of cattle to the lettuce fields may have been a contributing factor to the outbreaks.
FDA, along with the Centers for Disease Control and Prevention, investigated the three outbreaks of several strains of E. coli that took place from September 2019 to January 2020. The outbreaks swept across the country and made nearly 200 people ill.
Some clusters of the outbreaks were traced back to a common grower with multiple ranches and fields located in Salinas, CA, the report read.
The on-farm investigations detected one of the outbreak strains in a sample on public land less than two miles upslope from a produce farm that had multiple fields identified in a traceback investigation. Other strains were found in closer proximity to where romaine lettuce crops were grown, including from a farm bordering cattle grazing land.
These findings suggest a potential contributing factor to the outbreaks has been the proximity of cattle to the produce fields investigated in traceback investigations.
“This is especially true when cattle are adjacent to and at higher elevations than produce fields,” the report read.
The agencies call on growers to assess and mitigate risks associated with nearby grazing lands and animal operations. The report did note the number of neighboring pasture cattle was far lower than the number of cattle held on a large concentrated animal feeding operation, “offering a useful reminder that high-density animal operations are not the only factor to consider.”
While FDA couldn’t narrow down a definitive source for the contamination of the romaine fields, “the agency considers indirect transmission of fecal material from adjacent and nearby lands from water run-off, wind, animals or vehicles to the romaine fields, or to the agricultural water sources used to grow the romaine, as possible routes of contamination.”
Potential factors
For the Salinas Valley region, where a vast number of produce in the U.S. is grown, FDA reported animal grazing or feeding operations of all sizes are considered the most likely source of one strain of E. coli. The agency said cattle are a persistent reservoir of the strain E. coli O157:H7.
Although the transmission route isn’t entirely known, the agency suggested several ways the lettuce may have been contaminated: run-off from adjacent grazing or feeding lands; direct transmissions by way of wind, animals, or farming equipment and crews; and application of agricultural water contaminated with fecal material from animal operations.
The report said a history of outbreaks in the region during the fall season (September to November) shows it as the highest risk season for romaine contamination.
FDA also noted wild animal activity such as rodents and birds could have also been a possible source or transmission of the pathogen. Although each producer is supposed to treat water from an open source with a sanitizer before applying to produce, investigators were unable to determine the effectiveness of the treatments.
Prevention
In order to prevent future E. coli outbreaks, the report recommended growers implement preventative measures such as buffer zones to adjacent cattle grazing lands and adding physical barriers; ensure adequate sanitation of agricultural water; increase traceability efforts; and improve root cause analyses. — Anna Miller, WLJ editor
