Hydroponic lettuce was seen as safe from salmonella
Countless salad lovers 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 fresh, typically raised nearby rather than in faroff fields. And a string of food poisoning cases linked to traditional soilgrown 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 investigated its causes, believed to be the first domestic inquiry into foodborne illness linked to hydroponic leafy greens. The agency, in a report on its findings, highlighted the need for proper storage of materials and the dangers of failing to ensure clean water in growing ponds, 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 CEO.
FDA investigators — who visited Brightfarms in July and August, 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 stormwater 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 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 spokesperson, 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 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, 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.”
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, Platt said in a statement.
Hydroponic agriculture has spread coast to coast in the past decade. Some operations, like BrightFarms, are in greenhouses. Others are on rooftops, or grown in towerlike structures.
The CDC estimates that salmonella bacteria — from many sources — cause about 1.35 million infections, 26,500 hospitalizations and 420 deaths in the United States every year.
While the FDA has not issued new rules in response to the 2021 outbreak, Veronika Pfaeffle, a spokesperson, said that the agency was aware of the growth of the hydroponic industry and would take any steps necessary to protect human health.
“CEA 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,” Pfaeffle said.
The FDA 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 stormwater basin on property next to the Brightfarms site. But federal investigators could not determine if the pathogen that contaminated the 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.
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 that 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 to control pathogens.
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 FDA 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,” Brackett said. “Any outbreak in which you can trace it, it’s always significant.”