FDA identifies potential source for major E. coli outbreak

Earlier this year, an outbreak of E. coli attributed to romaine lettuce rocked parts of North America. Over 210 people got sick, five of them losing their lives. And even though investigators were able to find the source, it proved tricky to figure out how the lettuce became contaminated in the first place.

Now, after months of investigation, the Food and Drug Administration (FDA) believes it may have found a promising lead: Irrigation canals on lettuce farms may have been contaminated with E. coli from a nearby cattle operation.

It’s been known for months that the implicated lettuce was coming out of the Yuma, Arizona area, a huge lettuce-producing region. But it was very difficult to pinpoint a specific farm. The FDA published a traceback diagram showing just how difficult it was — 15 points of service; nine distribution centers; six processors, growers and harvesters; 19 farms and 33 fields came together into an enormous web of many points where contamination could have initially occurred.

However, during its investigation, the FDA found that irrigation canal water samples had tested positive for E. coli O157:H7, the strain behind the outbreak. These canals ran towards multiple farms around Yuma.

E. coli O157:H7 is most commonly attributed to food that comes from cows, but it can turn up in produce that has been contaminated with traces of cow manure as well. Investigators determined that runoff from one large cattle feedlot may have drained into the irrigation canals, leading to the contamination of nearby lettuce.

This theory isn’t 100% confirmed, though, and other sources have different suggestions. NPR reports that one water quality specialist proposes that dust from the feedlot could have contaminated vulnerable frost-damaged lettuce through the air, for example. Regardless, farmers are looking at ways to prevent the situation from happening again, like moving fields further away from the main source of water or treating water with disinfecting chlorine.

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