Science

Hydroponic Lettuce Was Seen as Safe From Salmonella, Until an Outbreak

Countless saladlovers have embraced hydroponic produce, confident that baby lettuce, arugula and herbs raised indoors in greenhouses are safer than greens rooted outdoors in farm soil.

Hydroponic growers advertise their produce as singularly fresh, typically raised close to customers’ homes rather than in far-off farm fields. And a string of food poisoning cases linked to traditional soil-grown leafy greens from California and Arizona in recent years has heightened the attraction of locally raised hydroponic produce.

But a salmonella outbreak last summer that sickened 31 people in four states and was traced to a BrightFarms hydroponic greenhouse in Rochelle, Ill., revealed that even greens grown in roofed-in environments are vulnerable to contamination.

Though the outbreak was small, the Food and Drug Administration conducted an investigation into its causes, believed to be the first domestic inquiry into food-borne illness linked to hydroponic leafy greens. The agency, in a recently released report on its findings, highlighted the dangers that can result from failing to ensure clean water in growing ponds and the proper storage of materials, and recommended safety guidelines for hydroponic farms in general. The hard-hitting report amounted to a cautionary note for the hydroponics industry and a signal to consumers that its greens are not immune to pathogens.

In response to the outbreak, BrightFarms has developed a plan to strengthen its food safety and quality, according to Steve Platt, the company’s chief executive.

F.D.A. investigators — who visited the BrightFarms facility last July and August, at a time when the agency had curtailed its inspections because of Covid-19 restrictions — could not find the exact cause of the outbreak. But their testing found evidence, in an outdoor storm-water basin near the facility, of the salmonella strain that caused the outbreak, as well as evidence of a different salmonella strain in an indoor growing pond, the agency’s report states. (Salmonella infection, or salmonellosis, is typically spread when people eat foods contaminated with feces from infected animals. The bacteria attacks the intestinal track.)

The F.D.A. report found problems with the facility’s handling of the municipally supplied pond water, which is used when the leafy greens are cultivated in floating polystyrene rafts.

“Once in the growing ponds, the water is not routinely disinfected or otherwise treated,” the report noted.

Korrie Burgmeier, a BrightFarms spokeswoman, said in a statement for Matt Lingard, the firm’s vice president of agriculture and science, that in an effort to keep its water free of additives, BrightFarms does not regularly disinfect its water. Instead, he said staff members routinely test the water and treat it “if the testing shows a risk.”

While the F.D.A. report acknowledged that BrightFarms sampled the water for E. coli, and, when found, treated it with hydrogen peroxide and peracetic acid solution, investigators criticized the company for not having a “procedure or systematic approach to ensure adequate pond water treatment.”

They also criticized the facility for storing hydroponic growth material outdoors rather than in a shed, leaving it susceptible to bird droppings and animal intrusion. Such material is used to stabilize plants and provide nutrients for the roots.

Another shortcoming, the investigators said, was that BrightFarms did not adequately document “that cleaning and sanitizing of equipment, tools and buildings used in growing operations is routinely conducted in accordance with the firm’s procedures.”

Experts say the F.D.A. report reveals the potential for problems in the hydroponic industry known as controlled environment agriculture, or C.E.A.

“Honestly, that report is a good first step for everyone in C.E.A. to say, ‘All right, we need to do more,’” said Martin Wiedmann, a salmonella expert and a professor of food safety and food science at Cornell University’s College of Agriculture and Life Sciences.

Starting in mid-July, BrightFarms began recalling salad greens in several Midwestern states, according to the C.D.C. It also hired a food-safety consulting firm, Matrix Sciences, according to Mr. Platt, the chief executive.

“It is our goal to create the safest agriculture system possible,” Mr. Platt said in a written statement.

The company shared the guidance from both the F.D.A. and Matrix in a confidential briefing with hydroponic industry leaders, Mr. Platt said.

A colored scanning electron micrograph of Salmonella typhimurium. The strain of bacteria sickened 31 people last summer, and was found in a storm-water basin near the BrightFarms facility.Credit…Eye of Science/Science Source

BrightFarms, which operates six commercial farms in six states, was purchased last year by the conglomerate Cox Enterprises. It planned to expand its capacity by 200 acres in the next two years, with five new greenhouses on the East Coast and in the Midwest and Texas, Mr. Platt said in a statement.

Hydroponic agriculture has spread coast to coast in the past decade. Some operations, like the BrightFarms site, are housed in greenhouses. Others are on rooftops, or grown in tower-like structures.

Lori Hilliard of Lombard, Ill., was among the 31 people who fell ill from the BrightFarms outbreak. Those sickened ranged in age from younger than 1 to 86 years old, according to the Centers for Disease Control and Prevention.

She said she was new to hydroponic produce when she bought several containers of BrightFarms salad greens at a local grocery store last June.

Several days later, she recognized something was wrong.

“These were the most bizarre body aches I’d ever had,” said Ms. Hilliard, a certified medical assistant at a large area medical group. The symptoms worsened, and she developed a fever, cramping and the worst diarrhea of her life.

Her husband drove her to an emergency room, where she was erroneously diagnosed with viral gastritis. Back home, the diarrhea continued, causing her to rush to the bathroom as often as 15 times a day.

“A couple of times, it felt like labor,” Ms. Hilliard said. “I was just screaming from the pain.”

Her doctor provided stool testing kits. Soon after, she received a call from the DuPage County Health Department, saying that she had salmonella poisoning. When she was asked if she had eaten BrightFarms lettuce, the puzzle pieces clicked together.

Even now, she said, she does not feel completely healed. She reached a lawsuit settlement with BrightFarms for an amount she could not disclose based on the agreement, according to her lawyer, William Marler.

She rarely eats salads anymore, she said.

Asked about the lawsuit, Mr. Platt said: “We were saddened to learn Ms. Hilliard became ill. And while the root cause was not found in our farm, our insurers were able to reach a compassionate resolution.”

The C.D.C. estimatesthatsalmonella bacteria — from many sources — cause about 1.35 million infections, 26,500 hospitalizations and 420 deaths in the United States every year.

While the F.D.A. has not issued any new rules to date in response to the 2021 outbreak, Veronika Pfaeffle, a spokeswoman, said that the agency was aware of the growth of the hydroponic industry and would take any steps necessary to protect human health.

“C.E.A. practices, such as those used in hydroponic greenhouse operations, differ in important ways from practices used in open-field growing, and those unique differences must be addressed from a food safety perspective,” Ms. Pfaeffle said.

The F.D.A. took an estimated 300 samples of greens, water and other substances as part of its BrightFarms investigation.

A key discovery was the presence of Salmonella typhimurium — the strain that sickened the 31 people — in a storm-water basin on a property next to the BrightFarms site. But federal investigators could not determine if the pathogen that contaminated the leafy greens had originated in the basin and moved into the greenhouse, or if it had traveled off-site from the greenhouse to the basin, according to the report.

The investigators also found another form of the pathogen, Salmonella Liverpool, in an indoor growth pond at BrightFarms.

“This highlights the importance of minimizing sources of microbial contamination as well as operating and maintaining production ponds in a manner that does not result in the spread of pathogens to product,” the report says.

Researchers at the University of Arkansas combed through past science journal articles to better understand the potential risks of pathogens in leafy vegetables grown hydroponically. Their study, published in Horticulturae in 2019, concluded that human pathogens “are readily internalized within plant tissues via the uptake of contaminated nutrient solution through the root system.”

Kristen E. Gibson, one of the study’s authors and an associate professor of food safety at the University of Arkansas, has been working with the U.S. Department of Agriculture on hydroponics research, searching for strategies that might control pathogens, she said.

Federal and state officials looking for the sickened BrightFarms consumers were aided by whole genome testing, a DNA fingerprint that can link a consumer with food poisoning to the producer at the source of the illness.

Not every outbreak can be traced back. And most people with food poisoning don’t report it, said Robert Brackett, a former F.D.A. food safety director who is senior vice president and dean of the industry training arm of the Institute for Environmental Health.

“They stay home; they don’t go to their doctors,” Mr. Brackett said. “Any outbreak in which you can trace it, it’s always significant.”

One group paying attention to the report is the CEA Food Safety Coalition, formed in 2019 by leading producers, including BrightFarms, according to its executive, Dr. Elisabeth Hagen, a former U.S.D.A. under secretary for food safety.

The coalition, with about 30 members, released standards for leafy greens last spring, focusing on risks related to water, structural design and pesticide use, Dr. Hagen said.

C.E.A. producers can seek a certification seal to display on their packaging if the coalition finds they adhere to the group’s standards.

Others have called for more oversight. Sarah Sorscher, deputy director of regulatory affairs at the Center for Science in the Public Interest, a nonprofit consumer group, said Congress should provide more funding to the F.D.A. to speed inspections of hydroponic farms.

Trevor Suslow, a consultant and professor emeritus in plant sciences at the University of California, Davis, urged hydroponic growers to follow the agency’s guidelines, which include recommendations on proper sanitation and clean water safeguards.

“Step away from, ‘It’s grown indoors, there’s no risk,’” he said. “That doesn’t seem to be responsible messaging.”

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