lettuce growing in a field

In the fall of 2019, at least 188 people were sickened in three separate E. coli O157:H7 outbreaks that were linked to romaine lettuce and leafy greens grown in Salinas, Calif. The Food and Drug Administration says it still doesn’t know exactly how the greens were contaminated, according to an FDA report released Thursday. But the most likely contributing factor, according to the report, is that disease-causing fecal matter from cattle grazing nearby may have been transported down to water sources and lettuce farms below.

“We’re calling on leafy greens growers to assess and mitigate risks associated with adjacent and nearby land uses, including grazing lands and animal operations,” Frank Yiannas, deputy commissioner for food policy and response at the FDA, said in a statement.

The fact that the FDA is conducting these investigations is encouraging, says Sana Mujahid, Ph.D., manager of food safety research at Consumer Reports. But she and other CR experts say more will be needed to truly improve food safety for leafy greens. 

E. coli O157:H7 is a form of the bacteria known as Shiga toxin-producing E. Coli (STEC), which can cause severe illness and in some people a potentially fatal form of kidney disease.

More on Leafy Greens

It’s not surprising that FDA investigators concluded that cattle grazing operations were a likely source of contamination, says Bill Marler, a food safety lawyer in Seattle. These bacteria contaminate the water and soil on lettuce farms when cattle manure that contains E. coli is transported from the area where the cattle graze, and experts have long connected cattle farming to E. coli contaminated greens.

“It’s obvious what the problem is, but the solutions are not going to be easy” because it’s hard to convince farmers they need to add more distance between areas where cattle graze and those where greens are grown, says Marler, who has represented dozens of clients sickened by E. coli linked to romaine lettuce and leafy greens. 

What the Report Found

FDA investigators and other federal and state partners studied fields that had been linked to the three Salinas romaine outbreaks in 2019. They took samples at farms that contaminated greens had been traced back to, and analyzed the soil and fecal matter found on public lands where cattle graze nearby.

Genetic analysis showed that the bacterial strains that caused the three 2019 outbreaks were not related, according to the FDA report, meaning the contaminated greens may have come from different sources. But the particular E. coli O157:H7 strain that was responsible for the largest of the three outbreaks was also found in samples of soil and fecal matter from an area where cattle graze less than 2 miles uphill from one of the lettuce farms linked to the outbreak.

Other types of STEC (different from the O157 strains) were also found in the area, according to the report, indicating the contamination may be widespread. A water sample from the nearby Salinas River was also found to have E. coli O157:H7, though investigators said the farms involved in the outbreak didn’t use river water as agricultural water.

The investigators said in their report that it’s not clear exactly how the bacteria traveled from the cattle-grazing land to the lettuce fields. But “E. coli-tainted manure can run off down hills and into rivers, contaminating water sources,” Keith Warriner, Ph.D., a professor in the department of food science at the University of Guelph in Ontario who has studied foodborne illness linked to produce, previously told Consumer Reports.

Concentrated animal feeding operations (CAFOs), which may contain thousands of cattle, were thought to be the source of contamination in many leafy green-related E. coli outbreaks. But in this case, the report noted, the cattle populations in nearby fields were far lower than those found in large CAFOs. That indicates that even smaller cattle operations near romaine fields may carry risks.

Additionally, FDA investigators determined that there were genetic links between some of the bacteria that caused outbreaks in 2019 and bacteria that caused E. coli outbreaks in 2018, meaning that the bacteria may be so widespread that they’re persisting in the environment.

Making Lettuce Safer

To help reduce E. coli contamination of leafy greens, the FDA report contained a number of recommendations, adding to recommendations released earlier this year in the agency’s 2020 Leafy Greens STEC Action Plan.

These include increasing the distance between uphill grazing lands and lettuce farms; adding physical barriers, such as walls and diversion ditches; assessing how nearby farming operations might affect water sources; improving record-keeping to make it easier to track down the source of an E. coli outbreak; and launching investigations to find the original source of any foodborne-illness-causing bacteria found in produce, she says.

“California leafy greens growers are pledging to incorporate findings” from the report, the California Leafy Greens Marketing Agreement (LGMA) said in a statement.

“Information from this new FDA report will be extremely valuable as we further strengthen our practices both in and around our farms,” Dan Sutton, general manager of Pismo Oceano Vegetable Exchange, which grows leafy greens in San Luis Obispo County, added in the LGMA statement.

Between 2006 and 2019, romaine and other leafy greens like spinach were connected to at least 46 multistate E. coli outbreaks, according to the Centers for Disease Control and Prevention. And a recent CDC analysis highlighted the need for action on foodborne illness—investigators found that the number of foodborne illnesses in 2019 were the same or greater compared with previous years, depending on the type of bacteria involved. (If you are concerned about foodborne pathogens in greens, check out our tips on the safest ways to eat salad.)

“The FDA’s report demonstrates the need for the agency to finalize the water quality and testing requirements under the produce safety rule from 2015,” says Brian Ronholm, director of food policy at Consumer Reports. “Also, when you combine these findings with the recent report from the CDC that concluded no progress has been made in reducing the infection rates for foodborne pathogens, it seems that more effective on-farm interventions will be necessary to reduce foodborne illness rates.”

Mujahid, Consumer Reports’ food safety research manager, adds, “As CR has said before, the FDA needs to have the authority to investigate animal feeding operations for pathogens that may infect crops like lettuce.” And as required under the Food Safety Modernization Act, the FDA should issue a list of high-risk foods and place leafy greens on that list.