It’s not been a great year for salad lovers; both the US and the UK have seen significant outbreaks of foodborne illness linked back to salad vegetables. But what is it about our favorite crisp and fresh ingredients that can make them a potential source of such unpleasantness?
How often do these outbreaks happen?
The US has so far seen two salad-linked foodborne illness outbreaks in 2024: one traced back to contaminated cucumbers and the other to organic carrots, the latter of which is still ongoing. There might be another one before the year’s end too, with another potential case of Salmonella-contaminated cucumbers popping up at the end of November. However, 2024 is far from the first year this kind of thing has happened.
According to data from the Centers for Disease Control and Prevention (CDC), from the beginning of 2020 to the present day in 2024, salad vegetables, seed sprouts, and leafy greens have been linked to 12 different outbreaks (potentially more depending on what people put in their salad) of foodborne illness in the US.
These veggies had all been contaminated with strains of bacteria, including Salmonella, Escherichia coli, Listeria, and Cyclospora.
How salad is grown and processed
To grow the salad ingredients we enjoy requires water – and that’s a potential route for contamination, whether it’s the result of flooding or poor irrigation practices. For example, the multistate outbreak of Salmonella Braenderup that occurred in June 2024 was traced back to cucumbers grown in untreated canal water. Yummy.
Contamination via water isn’t limited to a single instance either, nor to the US alone.
In a 2019 study, Professor in Medicine at the University of East Anglia and an expert in foodborne disease Paul Hunter and colleagues examined 35 outbreaks of Shiga toxin-producing E. coli linked to salad, sprouted seeds, or leafy greens from around the world, including how the contamination may have occurred.
“The most common identified reason that the product had been contaminated was contaminated water during growth, harvesting or processing,” Hunter told the Science Media Centre.
Beyond water, the European Food Safety Authority has found that proximity to animal rearing operations, the use of untreated manure or compost, and cross-contamination from processing equipment or by food handlers are also key risks for leafy greens contamination.
How we prepare them
How salad vegetables are prepared can also factor into their role in making people sick. A quick glance at a food safety guide will tell you that one way to get rid of bacteria is by cooking – but that isn’t really an option for salad.
What about washing it away? Turns out that’s easier said than done.
Speaking to CBC News about a spate of lettuce-linked E. coli outbreaks back in 2017 and 2018, Lawrence Goodridge, a professor of food safety at McGill University, said: “The bacteria can be stuck on the surface of the lettuce, it can even get inside the lettuce.”
“So if you wash it, you might remove some of the bacteria, but you’re not removing 100 per cent. And we know in some cases, when we look at historical outbreaks of E. coli, even ingesting one single bacterial cell was enough to cause illness.”
