Poopy salad greens still plague public health

With pandemic stress-eating colliding with holiday feasts last week, many of us may be eyeing some healthy salads in the coming days. But if there’s one constant we can rely upon in this year of upheaval—it’s the enduring possibility that our leafy greens may be laced with poopy bacteria.

The Centers for Disease Control and Prevention currently has three open investigations on Escherichia coli outbreaks—two directly linked to leafy greens and the other involving a bacterial strain that caused an outbreak in 2018 linked to romaine lettuce.

Meanwhile, the Food and Drug Administration had issued four separate safety alerts for recalled salad fixings this month. Three of the recalls involved romaine lettuce—a now notorious source of gut-busting bacteria—for potential E. coli contamination. Over the past weekend, the FDA added baby spinach to the list, another common culprit, for potential Salmonella contamination.

Only one of the recalls has been directly linked to an outbreak so far. On November 6, Tanimura & Antle Inc. voluntarily recalled its packaged single head romaine lettuce (labeled as being packed on Oct. 15 2020 or Oct. 16, 2020) over possible E. coli contamination. Routine lab testing in Michigan picked out a strain of E. coli in the soiled salad sample that was found to be sickening people. In all, 12 people across six states were infected with that particular strain, and five of the infected people were hospitalized. Of 11 people interviewed, all reported eating various types of leafy greens, including romaine lettuce (5), spinach (5), iceberg lettuce (3), and red leaf lettuce (3), the CDC notes.

Poopy possibilities

The agency noted a similar pattern in another E. coli outbreak investigation, which was last updated November 23. In this outbreak, 39 people have been sickened across 18 states, with 19 people ending up in the hospital. Of 22 ill people health investigators have been able to interview, all reported eating a variety of leafy greens, such as spinach (16), romaine lettuce (15), iceberg lettuce (12), and mixed bag lettuce (8). “No single type or brand of leafy greens or other food item has been identified as the source of this outbreak,” the CDC added.

In the third E. coli outbreak investigation, researchers haven’t fingered leafy greens specifically. The outbreak, which began back in June, has sickened 21 people in eight states, with eight people needing hospitalization. One person has died. The CDC notes that the E. coli strain in this outbreak was also behind a massive multi-state outbreak back in 2018 linked to romaine lettuce. That outbreak sickened 210 people across 36 states, sending 96 people to the hospital. Five people died. The CDC cautioned that “food linked to a previous outbreak alone is not enough to prove a link in another outbreak of the same strain. This is because different foods can be contaminated by the same strain of bacteria.” The agency noted that “several” people sickened in the current outbreak seemed to all be infected at the same restaurant. Still, health investigators haven’t identified a specific food as the source of the outbreak.

In all the outbreak investigations, researchers have identified strains of E. coli O157:H7—that is otherwise harmless E. coli strains that carry disease-causing toxins that originated in Shigella dysenteriae bacteria (aka Shiga toxins). In infected people, Shiga toxins cause stomach cramps, vomiting, and diarrhea (often bloody). Some people develop low fevers. In serious cases, the toxins can cause a type of kidney failure called hemolytic uremic syndrome (HUS), which can lead to permanent organ damage and even death.

The main source of these E. coli O157:H7 strains is the intestines of livestock, particularly cattle. They are often thought to make it to the leaves of salad greens via runoff from livestock farms and contaminated water sources used for crop irrigation. The massive outbreak in 2018, for instance, was linked to manure from a high-density cattle farm found contaminating canal water upstream of contaminated lettuce fields.