“Guarded optimism.” That’s the way Elston Grubaugh, general manager of the Wellton-Mohawk Irrigation and Drainage District in the eastern Yuma, AZ, growing area describes his thoughts about the current romaine lettuce season.

In 2018, an outbreak of E. coli O157:H7 infections linked to romaine lettuce grown in the Yuma area sickened 210 people and killed five. Reported in 36 states, it was the largest outbreak of E. coli O157: H7 the United States had seen in 10 years. 

In their search of the source of the problem, U.S. Food and Drug Administration investigators found some water samples from an irrigation water canal in the Wellton district tested positive for the same genetic strain of E. coli that infected the people sickened or killed in the outbreak.

E. coli is the shortened name of a bacteria called Escherichia coli that is found in the environment and intestines of people and animals. In people, some strains of it can cause infections, pneumonia, and kidney failure. Some strains of E. coli aren’t dangerous to people, but others such as E. coli O157: H7 can cause fatal infections.

Ideal growing conditions
Because the Yuma growing area is blessed with a mixture of day-after-day of sunshine and Colorado River irrigation water, it is an agricultural powerhouse. In combination with Southern California, it is often referred to as the nation’s “salad bowl.” The overall area represents a $4 billion industry and provides 90 percent of the U.S. grown leafy greens distributed in the United States every year.

In a typical year, about half of the acreage in the Yuma area is used for romaine lettuce.

The Wellton-Mohawk Irrigation and Drainage District lies 45 miles along the Gila River, but the district receives water from the Colorado River at Imperial Dam. The Mohawk Main Canal is 48 miles long and the Wellton Canal is 20 miles long. The area around Yuma is dry, desert land that receives very little rain. But thanks to irrigation, roughly 230,000 acres are used to grow a variety of crops, turning the desert into a vibrant green landscape in winter. 

For anyone who lives in growing areas other than the desert, the sight of the crops growing right next to the desert sand, all under a canopy of sunny blue skies, is breathtaking. The Colorado River water in the area’s irrigation canals is also beautiful — it does not look turgid — and is sometimes adorned with colorful wildflowers on its banks. 

A shock
“Shock, yes it came as a shock,” said Grubaugh, referring to the 2018 outbreak. “Quite a shock. We have not had a major outbreak since the district was formed in 1951.” 

The spring 2018 outbreak associated with romaine lettuce from the Yuma area effectively shut down the industry as consumers and commercial buyers, including restaurants and grocery stores, stopped buying all romaine.

It didn’t help that when the Yuma area’s growing season was done, another E. coli outbreak hit. It was traced to romaine lettuce from a farm in California. At that point, the U.S. Centers for Disease Control and Prevention went so far as to warn people not to eat any romaine at all. On top of that, the FDA called on the industry to voluntarily withdraw all romaine from the market and temporarily cease shipping.

So far so good
So far so good this year in the Yuma growing area, said Grubaugh. No reports of E. coli infections have surfaced. Yet, he also points out it was about this time in 2018 when the reports of lab-confirmed E. coli infections started.

“Like everyone else, we are hoping we won’t have a repeat this year,” he said.

He’s basing his “guarded optimism” on some changes the district and the growers have made this year.

Organizations in Arizona and California referred to as Leafy Greens Marketing Agreements, have set out requirements for their members who grow romaine and other greens.

To maintain membership, growers must use buffer zones between produce fields and animal feedlots, also referred to as concentrated animal feeding operations (CAFOs). Those buffer zones have been expanded from 400 feet to 1,200 feet. Food-safety specialist Vicki Scott of the Yuma Safe Produce Council said some growers are opting for distances greater than that. Grubaugh said he has heard that some buyers are requiring that the leafy greens fields be a full mile away from feedlots.

This change in distance was triggered by an environmental assessment of the area done by FDA and CDC, among others, that found samples of water collected in a 3.5 mile stretch of the Wellton canal contained the same E. coli O157:H7 strain that sickened outbreak victims. 

The locations of wher the E. coli was detected were approximately one mile upstream of the Five Rivers feedlot — which has a capacity of 120,000 cows — adjacent to it and approximately one mile downstream from it. 

The FDA’s traceback investigation identified 36 growing areas on 23 farms as potential sources of the contaminated romaine consumed during the outbreak.

In 2018, investigators collected six samples from the Wellton-area feedlot — composted manure, dry manure, fresh manure, spilled fresh manure, well water, and feedlot drainage water from a retention pond. The outbreak strain was not detected in any of them.

But the report concedes the sampling was limited, especially considering how large the feedlot is, and that it has a high turnover of steers. It also points out that the limited sampling was performed after the outbreak had occurred. The first confirmed outbreak patient became sick on March 13, 2018, but the samples were not collected until early June 2018.

E. coli O157:H7 can come and go in cattle herds. And, as the report points out, “it is not possible to draw statistically valid conclusions . . . based on the number of samples collected and when they were collected relative to the outbreak.”

The investigators also failed to detect any signs of E. coli in the farm fields near the feedlot. However, they took the samples in June, well after the outbreak and more than two months after harvest around Yuma had ended. After harvest, growers routinely plow up the fields in preparation for the next crop, exposing the soil to sun, dry air, and heat that quickly kill E. coli bacteria.

According to the environmental assessment report, because the Yuma region’s growing season had already ended weeks before the assessment began, there were no leafy greens available for testing by the outbreak investigation team.

Grubaugh said one of FDA’s theories is that shallow groundwater from the feedlot was contaminated. “As we pumped the groundwater, did it somehow contaminate the irrigation canal?” he said.

However, samples collected from the feedlot’s wells and from adjacent district drainage wells didn’t show E. coli.

Grubaugh also said canal repairs after the outbreak investigation may have been a step toward one solution. The district hopes to draw down the canal again this year for additional concrete repair work. 

“We would like to take the canal out of service for a few days to see if it makes any difference, he said.

In August 2018, investigators with the environmental assessment team returned to the Yuma growing area and took additional ground water and irrigation canal water samples. The sampling sites included the three Wellton irrigation canal sites that tested positive in June. None of the samples collected in August were positive for the outbreak pathogen.