Forty people died and more than 3,500 became ill this spring as a result of ingesting E. coli-contaminated vegetable sprouts grown on a German organic farm. Investigators do not know the source of the extremely virulent strain of E. coli, but one thing is certain: Making sprouts safe for consumers has been a concern and a topic of ongoing research and investigation in the United States.
According to the U.S. Department of Agriculture (USDA), raw alfalfa sprouts have been recognized as a source of foodborne illness, including E. coli O157:H7 and Salmonella, since 1995. In 1996, Japan suffered the worst E. coli outbreak in history when radish sprouts made thousands sick and killed at least twelve. According to the Food Poison Journal, since 1990, raw or slightly cooked sprouts have caused 2,273 illnesses, through 37 U.S. outbreaks. The U.S. Food and Drug Administration (FDA) estimates that outbreaks linked to sprouts account for 40 per cent of all produce-related foodborne illness! FDA materials indicate sprout seeds are the likely source of contamination in most sprout outbreaks.
Organic Farming: The Problem?
It is not yet known whether the German outbreak was related to the fact that the sprouts were produced using organic farming methods. Could composting practices be implicated? In the U.S., the Organic Trade Association guidelines specify that raw manures must be composted to Natural Resources Conservation Service standards to destroy pathogens, whereas European Union guidelines are focused on environmental contamination from factory farms. There are no direct references to the use of sanitizers in the EU guidelines, and allowable disinfectants in the U.S. include chlorine levels in water no higher than those permitted in U.S. drinking water. These standards would seem to increase the risks of contamination of organically grown sprouts.
Sprouts are Unique
There are serious difficulties in decontaminating pathogens during the sprout production and handling process. For example, sprouts cannot withstand abrasive physical washing because of their fragility, and seeds have a somewhat oily surface that may repel water. The uneven surfaces of seeds provide areas where germs can hide and remain viable, even protected from a disinfecting soaking solution, such as calcium hypochlorite. Additionally, seeds can harbor germs internally; and seeds are sprouted in warm, moist environments—ideal conditions for bacterial growth. For these reasons, the Centers for Disease Control and Prevention advises that children, the elderly, and persons whose immune systems are compromised should not eat raw sprouts. The FDA recommends cooking sprouts thoroughly to reduce the risk of illness.
Monitoring and Decontaminating Seeds and Sprouts
Seeds of different vegetables used for sprouts vary in their resistance to disinfection treatment. In 1999, USDA microbiologists developed a combined irradiation and chlorine treatment that not only kills E. coli and Salmonella, but also extends the shelf life of alfalfa sprouts from about five days to more than a week (see article). However, at least one industry expert, Lincoln Neal, in an interview for a June 20, 2011, article in Food Safety News, said irradiation sufficient to kill foodborne pathogens will almost invariably damage the seed germ, the heart of the seed needed for germination. Weakened seeds, he said, are vulnerable to contamination, negating the benefit of irradiation. Neal is president of a company that provides purification, propagation and processing systems for sprout companies in North America.
FDA guidelines recommend sprout producers test spent irrigation water to detect the presence of pathogens in the sprout environment: “Spent irrigation water that has flowed over and through sprouts is a good indicator of the types of microorganisms in the sprouts themselves and the microflora in spent irrigation water is fairly uniform.” FDA recommends a sampling plan that ensures representation of each production lot. Because seed is often the source of contamination, according to FDA, and “a single contaminated seed lot can result in contamination of multiple production lots of sprouts,” every contaminated batch, the seed lot used to produce that batch, and any other sprout production lots that were made from the same seed lot should be discarded. Additionally, all surfaces that have contacted the contaminated materials should be thoroughly cleaned and then sanitized to avoid contaminating subsequent batches of sprouts.
The Food Safety News article describes several solutions developed to destroy germs associated with industrial production of sprouts:
- Sanitize the seeds as they are sprouting by “repeatedly flushing the inside of the seed hull with disinfectant solution at the moments the seed ‘changes, opens, morphs, and detaches to release the sprout.’”
- Pasteurize seeds by dipping them in very hot water to kill pathogens both on and under seed surfaces.
- Maintain multiple sprouting rooms in production facilities to prevent cross-contamination; install automatic sanitizers that spray disinfectants on the floor where equipment and people enter.
Time is of the essence during foodborne outbreak investigations, as the unfortunate toll of the German outbreak demonstrates. The longer an outbreak lasts, the greater the risk of public consumption of contaminated foods. In January 2011, President Obama signed into law the Food Safety Modernization Act. One of the provisions of the Act requires the FDA to establish a product tracing system to effectively track and trace food. The agency will establish a list of high-risk foods and additional recordkeeping will be required for these foods. The goal is to establish a traceability system that is consistent, speedy, covers the entire supply chain, has electronic records, has interoperable systems, and covers domestic and imported foods.
Sprouts can be a healthy, nutritious food, but consumers should be aware of the potential risks associated with their production. Can consumers protect themselves by washing the sprouts they bring them home? FDA researchers have found that if foodborne pathogens such as E. coli and Salmonella are on the finished sprouts, washing them only minimally decreases the amount of contamination. Hopefully, through the combined efforts of sprout producers, industry innovators and a new government track and trace system, U.S. consumers will not experience a repeat of the devastating German E. coli outbreak.
Linda Golodner is President Emeritus of the National Consumers League and Vice Chair of the Water Quality & Health Council.