How E. coli in our salads has led to the hospitalization of 10 people for hemolytic uremic syndrome


This time it begins in Salinas, Calif.

The newest outbreak of Escherichia coli, known as E. coli, in romaine lettuce was announced on Fri., Nov. 22 by The Centers for Disease Control and Prevention (CDC). Consumers know the drill: the CDC and FDA recommend tossing out all lettuce harvested from the Salinas region (as indicated by labels) and that consumers refrain from buying similarly labeled or unlabeled products.

As of Dec. 2, the CDC reports that there have been 58 documented hospitalizations across 23 states. Of the infected patients, 10 have developed hemolytic uremic syndrome (HUS), which results in kidney failure and is potentially fatal.

Whereas most strains of E. coli reside peacefully within human intestines, this is not the case with the particular strain of E. coli that contaminates romaine lettuce, enterohemorrhagic E. coli O157:H7 (EHEC). The pathogen is appropriately referred to as ‘enterohemorrhagic’ for its ability to cause intestinal bleeding, which it does by producing severely damaging toxins. Thus, O157:H7 is also known as STEC for ‘Shiga toxin-producing E. coli.’ 

As STEC lives in the intestines of mammals, notably cattle, it is likely transmitted to our unassuming salads via contact with animal feces, followed by insufficient disinfection of the produce. STEC is virulent in humans, but other animals may be entirely unaffected. 

Concealed in our romaine lettuce salad, STEC infiltrates the digestive tract. Typically, pathogens from food don’t make it past the acidic environment of the stomach, where the pH is around 2. STEC, however, is fairly acid-resistant. As a result, it is undeterred by the low pH environment of the stomach. It continues, uninhibited, along the digestive tract to the intestines.

As the name suggests, STEC’s virulence is due to the potent Shiga-toxins it produces. STEC is known to produce both Shiga-toxin I and Shiga-toxin II. When these toxins enter host cells lining the intestines, they disable ribosomal RNA, inhibiting the cell’s ability to perform protein synthesis.

The result of the tissue damage is severe cramping, diarrhea, both bloody and nonbloody, and, for an unfortunate 2 to 7%, hemolytic uremic syndrome (HUS).

HUS occurs when Shiga-toxins are absorbed from the intestines into the bloodstream through the same process by which nutrients from food are also absorbed into the bloodstream. As the toxins circulate throughout the body, they bind to the cells lining the blood vessels in organs such as the kidney or the brain. Damage to kidney blood vessels results in blood clotting and depletion of red blood cells, ultimately causing kidney failure. 5 to 10% of HUS cases prove fatal.

Math and physics teacher Sushma Bana is no stranger to salads. She’s a vegetarian, she explains, and greens are a staple of her meals. She loves to mix in beans, fruits, nuts, you name it — oh, but no dressing.

Most importantly, however, Bana makes it clear that it’s necessary to be cautious and informed when it comes to leafy greens.

“You keep hearing, you know, sometimes it’s the spinach, then it’s the lettuce, then it’s something else,” Bana said. “There is nothing called being too careful.”

Although she has never been a victim of illness caused by STEC, she takes preventative measures while preparing her lettuce. Among her routine protocols are triple washing her salads, wiping down the bags the produce is sold in, and never storing lettuce for more than a week.

“When the leaves start to wilt and […] sometimes they become a little […] slimy […] on top,” Bana said. “Yeah, so then that’s the time to throw it away.”

Bana also cautioned against cross contamination while cooking, particularly for those who enjoy meat with their lettuce.

“Sometimes people who eat meat, they have that cross contamination. […] You know, they’ll cook poultry or something, chicken, and […] they do not clean up their knives and other things. So there is that cross contamination.”

To avoid cross-contamination, thoroughly washing counters, utensils, cutting boards, and, of course, hands is crucial, especially after handling raw meat. The same applies to other activities as well: always wash hands after petting animals or changing diapers.

Once an outbreak is announced, Bana promptly tosses all at-risk produce. This is corroborated by CDC and FDA guidelines, whose current list of produce to toss out includes lettuce labeled with “grown in Salinas”, lettuce without an indicated growing region, and salads or wraps with unspecified varieties of lettuce.

For now, while the CDC warning remains ongoing, it might be in the best interests of one’s kidneys to skip on that romaine lettuce salad.