I worked in my garden today and spent time with our six chickens, but the E. coli O104:H4 that has killed at least 45 and left over 800 with acute kidney failure in Europe and the United States was not far from my mind. As of yesterday, the “German” E. coli outbreak appears to have spread to France with at least ten sickened and a British sprout supplier under the microscope for both the France and German outbreak.

After a well-needed shower and a glass of wine, I got to thinking again about bad seeds and the problems with sprouts and sprout seeds. It is not like WE have not been adequately warned. In 1999, an outbreak of Salmonella enterica serotype Mbandaka occurred in Oregon, Washington, Idaho, and California. Based on epidemiologic and pulsed-field gel electrophoresis evidence from 87 confirmed cases, the outbreak was linked to contaminated alfalfa seeds grown in California’s Imperial Valley. Trace-back and trace-forward investigations identified a single lot of seeds used by five sprout growers during the outbreak period. Cases of salmonellosis were linked with two sprout growers who had not employed chemical disinfection; no cases were linked to three sprout growers who used disinfection. This natural experiment provides empiric evidence that chemical disinfection can reduce the human risk for disease posed by contaminated seed sprouts.

It will be interesting to see if this recent bad seed outbreak shakes out to be Thompson & Morgan Seeds and if substantive changes happen – before the next outbreak. Shout out to William E. Keene.

FDA has recognized the problem with seeds. In a 2008 letter to sprouters in the United States the FDA wrote:

As you are aware, seeds are considered the most likely source of contamination in most sprout-associated outbreaks. Yet, we continue to see sprouters who purchase seed without requirements or procedures in place to evaluate the seed before use.

Some sprout growers may require or obtain a negative test on each incoming shipment of seed. However, many only require 25 grams of seed to be tested from a lot composed of several thousand pounds of seed. Because the sample size is so small, and pathogens are likely not uniformly distributed throughout the lot, the probability of detecting pathogens in a large seed lot, using a single 25 gram sample, is very low if pathogens are indeed present.

Although there are currently no USFDA guidelines or state statutory requirements in this area, the incoming seed represents a known hazard that should be addressed with an effective and statistically valid procedure for evaluation of seeds prior to use. These procedures should include visual examination of the seed bags and examination of a representative sample of seeds from the lot for evidence of contamination, such as rodent urine or holes in seed bags, rodent droppings, or insects. If evidence of contamination exists at this stage, sprout growers should consider declining the lot. Further assessment should include testing of a statistically valid sample of incoming seed, and/or testing of spent irrigation water from a statistically valid sample of sprouted seeds before acceptance/use of the entire lot.

In more detailed 1999 Guidance to the sprout industry, the FDA suggested:

All parties involved in the production of sprouts — seed producers, seed conditioners, and distributors, and sprout producers — should be aware that seeds and sprouted seeds have been recognized as an important cause of foodborne illness. The following recommendations identify the preventive controls that the Food and Drug Administration (FDA) believes should be taken immediately to reduce the risk of raw sprouts serving as a vehicle for foodborne illness and ensure sprouts are not adulterated under the food safety provisions of the Food, Drug, and Cosmetic Act (the act). Failure to adopt effective preventive controls can be considered insanitary conditions which may render food injurious to health. Food produced under such conditions is adulterated under the act (21 U.S.C. 342(a)(4)). FDA will consider enforcement actions against any party who does not have effective preventive controls in place, in particular, microbial testing.

These recommendations are based on the recommendations of the National Advisory Committee on Microbiological Criteria for Foods (NACMCF, 1999) and elaborate on Compliance Policy Guide 7120.28 (CPG 7120.28).

Seeds for sprout production should be grown under good agricultural practices (GAPs) in order to minimize the likelihood that they will contain pathogenic bacteria. Seeds that may be used for sprouting should be conditioned, stored, and transported in a manner that minimizes the likelihood that the seeds will be contaminated with pathogens. For example, seed should be stored in closed or covered containers in a clean dry area dedicated to seed storage. Containers should be positioned off the floor and away from walls to reduce the possibility of contamination by rodents or other pests and to facilitate regular monitoring for pest problems.

Sprouters should implement appropriate practices to ensure that sprouts are not produced in violation of the act which prohibits the production of food under insanitary conditions which may render food injurious to health (21 U.S.C. 342(a)(4)). In addition to seed treatment and testing for pathogens (see below), sprouters should maintain facilities and equipment in a condition that will protect against contamination. Facilities with poor sanitation can significantly increase the risk of contaminating product. Sprouters should employ good sanitation practices as a standard operating procedure to maintain control throughout all stages of sprout production. Inadequate water quality and poor health and hygienic practices can all increase the risk of food becoming contaminated with pathogens. Sprouters may wish to review 21 CFR Part 110 which sets forth good manufacturing practices (GMPs) in manufacturing, packaging, or holding human food that cover these aspects of food production.

Seeds for sprouting should be treated with one or more treatments (such as 20,000 ppm calcium hypochlorite) that have been approved for reduction of pathogens in seeds or sprouts. Some treatments can be applied at the sprouting facility while others will have to be applied earlier in the seed production process. However, at least one approved antimicrobial treatment should be applied immediately before sprouting. Sprouters should carefully follow all label directions when mixing and using antimicrobial chemicals.

Because currently approved antimicrobials have not been shown to be capable of eliminating all pathogens from seed, sprout producers should conduct microbiological testing of spent irrigation water from each production lot to ensure that contaminated product is not distributed. Because testing for pathogens can be done with irrigation water as early as 48 hours into what is generally a 3 to 10 day growing period, producers who plan accordingly can obtain test results before shipping product without losing product shelf-life. Testing, whether done by the producer or contracted out, should be done by trained personnel, in a qualified laboratory, using validated methods. Additional information on sample collection and microbial testing, including how to sample and test sprouts when testing spent irrigation water is not practicable (as may be the case with soil-grown sprouts), can be found in a companion guidance document referenced below.

Traceback cannot prevent a foodborne illness outbreak from occurring. However, being able to trace a food back to it’s source quickly can limit the public health and economic impacts of an outbreak, if it occurs. Information gained in traceback investigations may also help prevent future outbreaks. Sprout producers, seed producers, conditioners and distributors should develop and implement systems to facilitate traceback and recalls in the event of a problem. All parties should test their systems in advance of a real problem.