Protecting families from contaminated food and water
All fields are required
Protecting families from contaminated food and water
Posted in E. coli,Our Blog on August 13, 2025
As much as 50% of all leafy greens E. coli outbreaks are linked to overhead spray irrigation water, says a recent study from Cornell University.
Of course, there are other factors that impact E. coli contamination in leafy green crops. Wild (and domestic) animal feces contamination, employee hygiene, processing plant sanitation, post-harvest cleaning activities, etc.
How big of a problem is E. coli in leafy greens? What could this information do for the industry?
Follow along for this, and more about overhead spray irrigation water and E. coli contamination in leafy green crops.
Outbreaks involving leafy are a big problem in the United States. In fact, the number of illness outbreaks associated with this crop have shown average increases year after year since 1996.
The toxin-producing germ, E. coli O157:H7 has been labeled the leading cause of those outbreaks. Other serotypes of E. coli, such as O26 and O111 also make notable appearances in historical records.
At least 4,274 laboratory confirmed illnesses, 766 hospitalizations, and 11 deaths were linked to seven outbreaks between 2015 and 2021. E. coli O157:H7 was the implicated germ. Leafy greens were the food source.
I’d say E. coli in leafy greens is a pretty big problem.
Like most foodborne infections, E. coli symptoms can vary from mild to severe. Certain life-threatening complications are common with toxin-producing E. coli serotypes like E. coli O157:H7.
Most people with an E. coli infection begin experiencing symptoms around three to four days after eating or drinking something contaminated with the E. coli bacteria. In some cases, people have become sick in as little as 1 day or as much as 10 or more days following exposure.
Common symptoms include:
Fever is not always a symptom. But if fever is present, it is usually lower than 101 °F.
Symptoms generally resolve within 5 to 7 days, though some may experience more severe illness or serious, life-threatening complications.
Complications like hemolytic uremic syndrome (HUS) arise when bacterial toxins cross the intestines and enter the bloodstream. These toxins damage the tiny blood vessels and break up certain blood cells. Those fragments can clog the filtering activities in the kidneys leading to kidney failure and other organ issues.
Those with HUS must be hospitalized for treatment and to monitor for kidney failure. Intravenous (IV) fluids and blood transfusions are typical treatments for HUS. About half of those hospitalized for this complication undergo dialysis (a short-term kidney replacement treatment that filters the blood to give the kidney’s a break).
Much of our leafy greens are from domestic sources. Excluding cilantro and certain herbs.
Around 90% of the leafy greens grown in the country are in California and Arizona. Both of which have established rules and a governing body known as Leafy Green Products Handler Marketing Agreements (LGMA).
These agreements involve certain guidelines and best practices to reduce the risk of contamination and harvesting these leafy green crops.
Among other things, LGMA provides a framework for pathogen prevention activities
Topics included in LGMA guidelines include:
While the California and Arizona LGMA are separate entities, they cover much of the same content. As one would expect for groups providing information on best practices. Not much changes from one state to the other.
One of the overlapping guidelines is prohibition of what they call “Type B agricultural waters.” This type of water cannot be used for overhead spray irrigation on leafy greens within 21 days of harvest. As opposed to “Type A agricultural waters.”
Type B agricultural water has very few restrictions. It can be anything from surface water to rainwater.
There are rules, however, to using this type of water.
Farms are not allowed to use this type of water up to 21 days before harvest for overhead spray irrigation water.
But what happens after that defined period? Is another water source required?
Yes and no.
A more strict class of water must be used for overhead spray irrigation. Defined as “Type A.” But Type B water can still be used on soil and drip irrigation.
There are concessions that if Type B water is treated to meet Type A standards, it can be used as if it were Type A water.
Type A irrigation water is typically harvested from underground water sources, like aquifers. This type of water is expected to be free from fecal matter and passes certain microbiological tests to ensure it is safe.
If necessary, it is treated to prevent the spread of infectious bacteria.
Overhead spray irrigation water deposits water above the plants, allowing potential contaminants to come into contact with the leafy green portion of the plant as opposed to seeping directly into the soil.
While overhead spray irrigation is simpler and presumably requires less infrastructure, applying potentially contaminated water directly onto the plant shortly before it is harvested could lead to product contamination.
Now that we understand the risks associated with overhead spray irrigation water, it is not much of a surprise that this water source is the cause of contamination events with leafy greens.
Usually if there is a rule for something, there is a reason for it. In this case, the 21 day before harvest rule for Type B irrigation water.
To better understand the cause of such outbreaks, Cornell University investigators reflected on historical data and created a risk assessment model to measure potential impacts of pathogen exposure. In this study, the model was described as a quantitative microbial risk assessment (QMRA) model.
Scientists ran certain points for pre- and post-harvest E. coli O157:H7 risk.
Based on historical data, 52 percent of romaine lettuce E. coli O157:H7 outbreaks were caused by untreated overhead irrigation water.
This data, input into the QMRA model, found the risk for these outbreaks reduced by as much as 96%.
That is significant!
Statistical evidence proving an aspect of existing guidance strengthens the necessity of these irrigation rules. However, since E. coli outbreaks still happen in leafy greens (more importantly, for this specific source), it further proves that the honor system and “guidelines” are not working.
Enforcement action is necessary. Clear rules and consequences for failed compliance are necessary.
What do you think?
If you’d like to know more about food safety topics in the news, like “Study Finds Overhead Spray Irrigation Water as Significant Risk for Leafy Greens E. coli Contamination,” check out the Make Food Safe Blog. We regularly update trending topics, foodborne infections in the news, recalls, and more! Stay tuned for quality information to help keep your family safe, while The Lange Law Firm, PLLC strives to Make Food Safe!
By: Heather Van Tassell (contributing writer, non-lawyer)