Seed Safety

International Specialty Supply

Supplying Sprout Companies Throughout the World

ISS

820 East 20th Street

Cookeville, TN 38501 USA

931 526 1106

Bob@sproutnet.com

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ISS Seed Screening for Human Pathogen Testing

Over the last decade commercially produced sprouts have been implicated in outbreaks involving thousands of people.

"In almost all cases, contaminated seed was the source of the contaminated sprouts both for Salmonella sp. and E. coli 0157:H7." Lester M. Crawford, D.V.M., Ph.D. Acting Commissioner of the FDA.

International Specialty Supply developed a method of screening seed for human pathogens that has been confirmed, referenced or recommended as necessary by:

The World Health Organization (WHO)

United States Food and Drug Administration (FDA)

United States Department of Agriculture (USDA)

California Department of Health

New South Wales Food Authority

South Australian Research and Development Institute

Ontario Ministry of Agriculture

The Center for Science in the Public interest

Resources for the Future

Food Standards Agency (UK)

The Campden Research Group

Food Safety Authority of Ireland,

National Center for Food Safety and Technology

Illinois Institute of Technology

Center for Food Safety and Applied Nutrition

Dozens of researchers and food safety experts.

The ISS Seed Screening Program has already prevented several lots of contaminated seed from being used in commercial sprout production.

According to the Center for Science in the Public Interest, in a paper called "Outbreak Alert! 2002, "Closing the Gaps in Our Federal Food-Safety Net", sprouts made up 7% of the outbreaks from fruit and vegetables during the period of 1990-2002 (September).

Produce Outbreaks

1990-2002

Vegetables
Potatoes	3%
Mushrooms	4%
Home-canned vegetables	5%
Sprouts	7%
Produce Dishes	9%
Other Vegetables	14%
Lettuce	11%
Salad	28%
Fruit
Melon	2%
Berries	4%
Other Fruits	13%
Total	100%

Table 1. Sprouts were suspected in 7% of the produce related outbreaks from 1990 to 2002

Sprout Related Outbreaks

Although there have been documented outbreaks in sprouts since 1973, federal regulators, public health officials, and the sprouting industry did not wake up to dangers associated with sprouting until about 1996. All parties concerned, including ISS, were bent on coming up with a way to sanitize the seed. Between 1998 and June 2006, there have been 36 reported outbreaks in the world that were attributed to sprouts. Twenty-seven of which involved US and/or Canadian sprout growers.

US Sprout Related Outbreaks 1996 - 2004

(FDA figures)

Year	Alfalfa sprouts & mixes with alfalfa sprouts	Clover sprouts	Mung bean sprouts	Total Outbreaks	Cases
1996	1	1		2	650
1997	3			3	277
1998	3			3	48
1999	5	1		6	389
2000			1	1	75
2001	1		2	3	88
2002	1		1	2	21
2003	5			5	52
2004	2			2	36
Total	21	2	4	27	1633

Table 2. Sprouts were suspected in 27 outbreaks and 1633 cases from 1996 to May 2005

Update: There have been additional US sprout related outbreaks reported since 2004.

Several of the Outbreaks Appear to be Related

Three separate bean sprout outbreaks of Salmonella were reported to be the SAME phage type. ^{(18,
24,
52,

89)} According to the Canada Communicable Disease Report,

“This outbreak represents the first known occurrence of SE PT 913 infection in humans.” ⁽¹⁸⁾

Three separate alfalfa sprout outbreaks of E.coli 0157:H7 were reported to have the SAME PFGE pattern.^{(31,

101)}According to the investigative report,

“These Pulse patterns had never been previously identified in the United States.”⁽³¹⁾

One outbreak reportedly involved FOUR strains of salmonella in ONE seed lot. From the report:

“Six opened packages of alfalfa sprouts were taken from cases' homes… Two packages were positive for S. paratyphi B var java, PT "Worksop", PFGE pattern A1. One package was positive for S. litchfield, one for S. thompson and one for S. newport; one package was negative.”⁽³³⁾

A 1996 outbreak appears to have matched the seed from a 1995 outbreak. From the report on the 1996 outbreak:

“PFGE testing on four isolates from University A students and two from University B students showed them to be identical to the 1995 outbreak strain.”⁽¹¹⁷⁾

The Source of Contaminated Sprouts is Contaminated Seed

The suspected scenario is that the seed is contaminated in the field by manure used as fertilizer, or by grazing animals, or in silos or bins by bird or mouse droppings and urine. The process of sprouting allows nearly ideal conditions of food, moisture, and warmth in which a single pathogen cell can proliferate into over one hundred thousand pathogen cells.

Since 1988, with one exception, seed have been the likely source of contamination in every outbreak in which the source was determined.

World Sprout Related Outbreaks 1988 - Early 2005

(Food Standards Agency, UK.)

Year	Pathogen	Cases	Location(s)	Type of sprout	Likely source of contamination
1988	S. Saint-Paul, S. Havana, S. Muenchen	148	Sweden	Mung	ND
1988	S. Saint Paul	143	United Kingdom	Mung	Seed
1988	S. Virchow	7	United Kingdom	Mung	ND
1989	S. Gold-Coast	31	United Kingdom	Cress	Seed and/or sprout grower
1990	S. Anatum	15	Washington	Alfalfa	ND
1992	S. enterica	272	Finland	Alfalfa	ND
1994	S. Bovis mordificans	492	Finland, Sweden	Alfalfa	Seed
1995	S. Stanley	242	Finland, 6 US States	Alfalfa	Seed
1995	S. Newport	154	Denmark (Probably USA and Canada)	Alfalfa	Seed
1995	S. Newport	133	7 US States, Canada, Denmark	Alfalfa	Seed
1996	E. coli O157:H7	5,727	Japan	Radish	Seed
1996	E. coli O157:H7	126	Japan	Radish	Sprout growers
1996	S. Montevideo and S. Meleagridis	492	California, Nevada	Alfalfa	Seed and/or sprout grower
1997	S. Anatum & S. Infantis	109	Kansas, Missouri	Alfalfa	Seed
1997	E. coli O157:H7	79	4 US States	Alfalfa	Seed
1997	E. coli O157:H7	108	Michigan, Virginia	Alfalfa	Seed
1997	S. Meleagridis	78	Canada	Alfalfa	Seed (organic)
1997	S. Senftenberg	60	California, Nevada	Alfalfa	Seed and/or sprout drum
1998	S. Havana	18	2 US States	Alfalfa	Seed
1998	S. Cubana	22	5 US States	Alfalfa	Seed
1998	E. coli O157:H7	8	California, Nevada	Alfalfa, Clover	Seed and/or sprout grower
1999	S. Mbandaka	75	4 US states	Alfalfa	Seed
1999	S. Muenchen	>157	Multistate, USA	Alfalfa	Seed
1999	S. Saint-Paul,	36	California, USA	Clover	ND
1999	S. paratyphi var Java	51	Canada	Alfalfa	Seed
1999	S. typhimurium	120	Colorado	Alfalfa	Seed
2000	Salmonella spp.	22	California, USA	Alfalfa	ND
2000	S. Enteritidis PT 4b	27	The Netherlands	Mung	Seed
2000	S. Enteritidis	75	4 US states	Mung	ND
2001	S. Enteritidis PT 913	84	Canada	Mung	Seed
2001	S. Kottbus	31	4 US states	Alfalfa	Seed
2002	S. Enteritidis	n/a	Maine	Mung	ND
2003	S. Saint-Paul	>9	Oregon, Washington	Alfalfa	ND

ND = Non Determined

Table 3. Seed was suspected in all but one of the outbreak in which a likely source was determined.

So Why Not Just Decontaminate the Seed?

A great majority of the research on alleviating sprout related outbreaks has focused on decontaminating the seed. And although the FDA went so far as to recommend that all commercially grown sprouts be produced from seed that has been sanitized with 20,000 ppm chlorine, no sanitizer has yet been found to be reliable at eliminating pathogens from seed without destroying germination.

If the pathogens were sitting on the seed coat, it would not be a problem, 200 ppm chlorine would do the trick. But the bacteria that are trapped in cracks and crevices in the seed coat appear to be protected from disinfectants, and there is evidence that some bacteria can be internalized within the seed itself. When a single pathogen cell remains alive, it will multiply back to levels as though no sanitation had ever been done.

To date no sanitation technique has been shown to completely eradicate pathogenic micro-organisms from either the seed or the sprouts.

Avoiding Outbreaks is Not Difficult if the Seed Is Not Contaminated in the First Place

In 2000, Bob Sanderson of Jonathan Sprouts came up with a simple, yet brilliant, idea. "If the problem is pathogens in the seed, why not just make sure there aren't any pathogens in the seed in the first place?"

In a collaborative effort between International Specialty Supply and Jonathan's Sprouts, a method was developed in which sprout growers and seed suppliers could substantially reduce the odds of there being pathogens in seed.

Seed is Generally Tested for Quality, Not Safety:

Seed sampling for seed borne plant pathogens has been practiced for many years and the statistical probabilities are well documented.

For over a hundred years seed has been tested for germination, purity, hard seed and other properties that relate to the quality of the seed. These are addressed in terms of percentage. For example, a seed lot might have a quick germination of 90% with 3% hard seed and 1% abnormal seeds, for a total germination of 94%. The statistical probabilities used to determine these percentages are extremely accurate.

Testing Seed for Human Pathogens can be Far More Accurate

When testing for pathogens, one is not looking for a percentage, but for any at all. If a single pathogen is detected, the lot is contaminated and cannot be used for sprouting purposes.

The entire sample, which in a truckload of seed can be over 20 Kg (44 lbs) (nearly a thousand times larger than a normal lab sample), is sprouted, which increases the bacteria level approximately 5 logs (100,000 times) in 48 hours. Then the runoff water is sampled, enriched, and tested for Salmonella, E.coli 0157:H7, and generic E.coli. A portion of the sprouts themselves are crushed and tested for Salmonella, E.coli 0157:H7, Listeria monocytogenes, Shigella and generic E.coli. They are also tested in a separate lab for Enterotoxigenic E.coli (ETEC) if generic E.coli is found.

ISS Seed Screening Procedures

The seed screening procedures, developed by International Specialty Supply for ISS Screened Sprouting Seed, can substantially reduce the risk of food-borne illness related to commercial sprout production. The process involves: seed sampling, seed inspection, sprout growing (enrichment), spent water sampling, enrichment of sampled water, and pathogen testing.

Every step is critical, must be precisely done, and accurately documented. No seed which has been sampled, enriched, and tested in this way, prior to use in production, has ever been implicated in an outbreak.

P Seed Sampling

In order to detect a pathogen in a lot of seed, you first need to “capture” it in the seed sample you intend to test. The probability of picking up at least one contaminated seed in a 40 lb seed sample is very high at an average contamination level of 4 CS/kg (4 Contaminated Seeds per 2.2 pounds of seed), but very low with smaller samples and smaller contamination rates.

Probability of Capturing a Pathogen in Alfalfa Seed Contaminated with Various Pathogen Levels Per Kilogram
Seeds Sampled		Pathogens (cs/kg)
Kilos	Seed Count	0.1	1	2	3	4	5	10	100
0.000002	1	0%	0%	0%	0%	0%	0%	0%	0%
0.00002	10	0%	0%	0%	0%	0%	0%	0%	0%
0.0002	100	0%	0%	0%	0%	0%	0%	0%	2%
0.002	1,000	0%	0%	0%	1%	1%	1%	2%	18%
0.02	10,000	0%	2%	4%	6%	8%	10%	18%	86%
0.2	100,000	2%	18%	33%	45%	55%	63%	86%	>99%
1	500,000	10%	63%	86%	95%	98%	>99%	>99%	>99%
2	1,000,000	18%	86%	98%	>99%	>99%	>99%	>99%	>99%
3	1,500,000	26%	95%	>99%	>99%	>99%	>99%	>99%	>99%
5	2,500,000	39%	>99%	>99%	>99%	>99%	>99%	>99%	>99%
10	5,000,000	63%	>99%	>99%	>99%	>99%	>99%	>99%	>99%
12	6,000,000	70%	>99%	>99%	>99%	>99%	>99%	>99%	>99%
25	12,500,000	92%	>99%	>99%	>99%	>99%	>99%	>99%	>99%
50	25,000,000	>99%	>99%	>99%	>99%	>99%	>99%	>99%	>99%
100	50,000,000	>99%	>99%	>99%	>99%	>99%	>99%	>99%	>99%

Probability (P) = 1-(C/T)^N, where (C/T) = assumed ratio of Clean seeds to Total, and N = Number of seeds sampled.

Table 4. Probability of Capturing a Contaminated Seed in a Twenty-Ton Lot of Alfalfa Seed Contaminated with Various Contamination Levels Per Kilogram.

The above table is theoretical and assumes even distribution in the bags that contain contamination. The number of contaminated seeds in an outbreak has not been investigated, nor has pathogen distribution. Although pathogen distribution in a lot is usually not homogeneous, distribution within the bags themselves likely is.

sprouting_seed_inspection P Seed Inspection

After a representative sample is taken, the composite sample of seed is inspected for indicators of contamination. This includes inspecting the bags for mouse urine or dropping, holes in the bags, insect larva, bird droppings, etc. The seed is then carefully inspected with both a magnifying glass and microscope to determine its fitness for human consumption. Again, we look for traces of visitation by animals and insects. In the process we have also found glass, seed that was blended with seed that had been treated with a fungicide, and other things.

P Sprouting (Enrichment)

The entire sample is sprouted. The seed is not sanitized prior to sprouting. In 48 hours the pathogens, if present, should have increased about 1,000,000 times, substantially increasing the probability of detection.

P Water Sampling and Testing

At about 48 hours, a sample of the runoff water is collected and enriched to make the pathogens multiply about 5 log (100,000 times) and the water is tested for salmonella, E.coli, and E.coli 0157:H7. The tests are run in duplicate.

P Sprout Testing New!

Some of the sprouts produced from the composite sample are sent to a separate lab. That lab crushes the sprouts and tests for Salmonella, E.coli 0157:H7, Listeria monocytogenes, Shigella and generic E.coli. They are also tested in a separate lab for Enterotoxigenic E.coli (ETEC) if generic E.coli is found.

P Documentation

Each step is thoroughly and accurately documented and signed by the person taking responsibility for completing each step of the process. The adage is, "It if isn't documented, it wasn't done."

P Pre-Screening

We add an extra step as well. Before we receive a shipment, we bring in a sample and inspect it, sprout it, and test it. We stop at the point of rejection. That is, if the seed does not pass visual inspection, we reject it without taking the time to sprout it out and test it for pathogens.

Generally if we receive seed with mouse dropping in it, that same processor will send bad samples time after time, and year after year. After a while, one learns who to stay away from. We are not only screening seed, we are screening seed processors.

ISS Seed Screening Discussion

Ground Rules

When it comes to seed sampling for human pathogens, distribution, sample size, and total contamination per lot are the factors that determine the probability of capturing a pathogen. Actual probabilities of detection require a knowledge of the quantity and distribution of pathogens in the particular seed lot. This information is not known.
There’s a possibility that two or more pathogens could be lodged on one seed. There is also a remote possibility that some contaminated seed could be clumped together. So we base probabilities on contaminated seed units (CS), which include clumps, rather than CFU. Seed, while being processed, does get mixed well enough for very accurate seed sampling estimates.
For ease of explanation, throughout the rest of this discussion all samples will be 25 grams and all bags will be 25 kilogram bags. So the sample size is always 1/1000^th of a bag or one seed per thousand seeds.
Although random sampling is generally the accepted practice in sampling, when sampling for the presence/absence of pathogens in seed, it is better to sample every bag. Although bags containing any pathogens may not be homogeneously distributed throughout a seed lot, the seed within each bag is fluid and usually very well distributed in the bag.

Larger Numbers of Samples Increase the Probability of Capture at a Given Contamination Rate.

Considering that we sample at least 1/1000 of the seed, the larger the lot, the larger the sample.

If seed is contaminated at 1 seed per kilogram, pulling one sample from one bag would only give you a 2.5% chance of finding it. But if you didn’t find it in the first bag, you have another change, with identical odds in the second bag. And the more bags there are, the more 2.5% chances you get at capturing a pathogen. You get a 2.5% chance enough times, say 400 times, and you have a 99.9% chance of capturing at least one of those contaminated seeds.

Contaminated	Bags &	Kg of	Contaminated	Probability
Seeds	Samples	Seed	Seeds per	of Capture
per kg	(Same #)	Sampled	Lot
1	1	0.025	25	2.5%
1	10	0.25	250	22%
1	40	1	1,000	63%
1	100	2.5	2,500	92%
1	400	10	10,000	>99%

Table 5. Different size lots in which all lots are contaminated a the rate of one contaminated seed per kilogram. The probability of capturing a pathogen increase as the contaminated seed per lot and the amount of seed sampled increase.

OK, What if the Seed Isn't Evenly Distributed and Pathogens are in Just a Few Bags?

Uneven distribution is a problem if you are trying to find a particular level of contamination, but is not as much of a problem if you are trying to find any at all. What matters most is the total number of contaminated seeds in the lot, not how many bags the contaminated seeds are in.

The chart below shows what happens if you sample various size lots, in which all lots have 2000 contaminated seeds, evenly distributed. Notice that if you have one contaminated bag you have 2000 contaminated seeds, and one pull will capture one or more of those seeds 86.5% of the time if distribution is even within that one bag. If you divided those 2000 contaminated seeds among 2 bags, you would have 1000 seeds per bag, but you have doubled the number of pulls, and the odds even out.

Bags	Bags	Contaminated	KG	Odds of
in Lot	Sampled	Seed per Bag	Sampled	Detection
1	1	2000	0.025	86.5%
2	2	1000	0.05	86.5%
10	10	200	0.25	86.5%
100	100	20	2.5	86.5%
800	800	2.5	20	86.5%

Table 6. Even Distribution among five different lots with the same (2000) total number of Contaminated Seeds (CS/lot, not CS/kg or CS/bag)

Our charts are actually based on the odds of capturing clean seed. Then we reverse the numbers in order to predict the number of contaminated seed. If you try this with small numbers, such as a few marbles in a cup, the odds will change as you move the marbles from cup to cup. However, there are about 12 ½ million alfalfa seeds in a bag. In this example, each bag in the lot that contains 800 bags has only 1997.5 more clean seeds than the lot with just one bag. That is a difference of only 0.00016%.

So the number of clean seeds remains virtually unchanged, and the probabilities, for all practical purposes, remain the same.

This next chart shows a large lot which, except in the bottom row, is unevenly distributed among 800 bags but does assume even distribution in the bags that do contain contaminated seeds. The first row has all 2,000 contaminated seeds in one bag. The odds, as in the previous chart are 86.5%. But it does not matter that you pulled seed from the 799 bags that are clean. You pulled one pull, from the one bag, that was so contaminated, that it gave you an 86.5% chance of finding one contaminated seed.

		Number of
		Contaminated	Samples
Bags		Seeds Each	Taken	Odds
Not	Bags	Contaminated	in the	of
Contaminated	Contaminated	Bag	Lot	Detection
799	1	2000	800	86.5%
798	2	1000	800	86.5%
790	10	200	800	86.5%
700	100	20	800	86.5%
0	800	2.5	800	86.5%

Table 7. Uneven Distribution in an 800 bag lot. If only a few bags are contaminated, they need to be very contaminated in order to have a good probability of capturing a pathogen. If many bags are contaminated, likelihood of finding a contaminated seed is strong even if contamination is low.

It should be noted that if you take those 1, 2, 10, 100, or 800 contaminated bags and put different levels of contamination in each bag you will still have an 86.50% chance of capturing a pathogen as long as there are 2000 contaminated seeds in the lot.

The assumption below is that the seed lot has 20,000 kg in 800 25kg bags from which 25 grams is sampled from each bag. There are 440,000 seeds per kg, or 8,800,000,000 (T) seeds per lot. 1,000th of the seed is pulled, giving a composite sample (N) of 8,800,000 seeds. As you can see, there needs to be about 5,000 contaminated seeds in the lot in order to get a 99% probability of capture. How many contaminated seeds are in any given lot that is contaminated is anybody's guess. There is no technology available to give even a good guess much less an accurate figure. Also, this is a theoretical model that assumes even distribution, not throughout the lot, just throughout the contaminated bags.

Probability (P) = 1-(C/T)^N, where (C/T) = assumed ratio of Clean seeds to Total, and N = Number of seeds sampled.

Contaminated Seeds per Lot	Probability of Capture
10	1%
20	2%
200	18%
1,000	63%
2,000	86%
5,000	99%
10,000	>99%

Table 8. Probability of Capturing a Contaminated Seed in a Twenty-Ton Lot of Alfalfa Seed Contaminated with Various Contamination Levels Per Seed Lot.

Some Question the Reliability of Seed Sampling Because There is a Possibility that the Contaminated Seeds Could be in a Corner of One Bag or in a Clump and Never be Detected.

To be clear, although these probabilities are not dependant on even distribution throughout the lot, the probabilities are dependent on even distribution throughout the bags that are contaminated. So if all 10,000 contaminated seeds in Table 8 are in the corner of one bag, the likelihood of capturing one or more of the contaminated seeds is very slim. If it is in the corner 100 bags the odds are still small. But if there is contamination in more than a bag or two, and, if it is a corner of the bag, it would most likely have occurred after the seed was bagged (mice eating their way through the bag). That is why bag inspection is an important part of seed screening.

We have to assume that these things happen from time to time and there is not always even distribution in the contaminated bag or bags. In this case, the probability charts are useless. But this scenario may not occur as often as one might think. The seed is harvested, transported, and dumped into a silo or bins.

sprouting_seed_production

Figure 1. Seed is mixed during harvest.

It is then poured or augured into the seed cleaning equipment, processed, and poured into a bag. The cleaning and grading process does not allow even two seeds to clump together or they won’t fit through the screens. Seed with pathogens are not likely to stay next to each other throughout this process. They will be somewhat, if not thoroughly distributed.

Figure 2. Seed is mixed during processing.

When Trying to Detect Plant Pathogens, Sample Sizes are Used and the Probabilities are Extremely High as Well.

When looking for plant pathogens, you are looking for frequency rather than any at all. In order to determine the percentage of pathogens in wheat, 8 kg is sampled for each 100 tons of seed. Then 300 seeds are pulled from that 8 kg for testing. Distribution of the plant pathogens is good enough that this method is very accurate. In the same lot size, we would sample and inspect the lot, and then 25 million seeds would be tested in order to find a single human pathogen!

Does Blending Make ISS Seed Sampling Less Reliable?

Yes and no. In the following example, two bags of seed, contaminated at the rate of 4 Contaminated Seeds/kg contain 200 contaminated seeds. If these two bags are blended in with 800 bags of non-contaminated seed, the new lot still has 200 contaminated seeds. The probability of detection, by pulling 802 samples is 18.5%. These are the same odds as if you had pulled one sample from each of the two contaminated bags before they were blended in.

	Large Lot	Small Lot	Combined
Bags	800	2	802
CS/kg	0	4	0.01
CS/lot	0	200	200
Samples	800	2	802
Seed Sampled	1/1000	1/1000	1/1000
Probability	N/A	18.5%	18.5%

Table 9. If a contaminated and non-lot is combined, the odds of capture will remain the same if the percentage (1/1000 in this example) remains the same.

However, using the ISS Seed Screening Protocol on the two bags, 3 kg would have been pulled for testing (instead of just two 25 gm samples). This increases your sample size from 1/1000 to 1/17th. The odds of capture go to 99.99%.

	Small Lot
Bags	2
CS/kg	4
CS/lot	200
Samples (3 kg Total)	120
Seed Sampled	1/17
Probability	99.999%

Table 10. Increasing the sample size from 2 pulls to 120 pulls, taken from the 2 contaminated bags prior to blending, substantially increases the probability of capturing a contaminated seed.

So it does not make any difference if the lot is blended or not, as long as the protocol is followed prior to blending. Or, if there is more than 120 bags (25gm x 120 = 3kg) in each lot that made up the blended lot.

Why is it Hit and Miss When Health Officials Try to Find Contamination in Seed That They Are Certain Caused an Outbreak?

Sample size, distribution, and the total number of contaminated seeds in the lot determine probability of capture. Seed companies can screen the seed when the entire lot is in tact. This is when the sample size will be greatest and the total number of contaminated seeds is at its highest.

By the time the epidemiologists determine that sprouts are most probably the cause of an outbreak, a good portion of that lot is gone, and a portion, if not all of the contaminated seed was used up in the outbreak. The outbreak could have easily consumed the entire number of contaminated seeds needed to have a high probability of capture.

What Happens to the Odds When the Minimum Sample Size Requirement is in Play?

The protocol requires drawing at least 3 kg for testing. But let's suppose it didn't. If there is light contamination, say 4 contaminated seeds per kilogram, and you sample one bag, the odds of finding it in those 25 grams are only 9.5%. Sampling 7 bags increases the odds of capture to over 50%. It would take sampling 47 bags (4,700 contaminated seeds and 1175 gm sample) to increase the probability of capture to 99%. So when you are testing a full truckload of seed (800 bags), contamination only needs to be in 47 (6%) of the bags, at very low levels, to get a 99% probability of capture.

But because the protocol is to draw at least 3 kg, sampling one bag, 120 times, would give you a 99.9+% chance of capture. Sampling 7 bags with 17.15 pulls each (120 total) will also give you 99.9+%, or pulling 2 pulls from each of sixty bags would give you the 99.9+% chance.

Bags Per Lot	1	1	7	7	47	47	800
CS/kg	4	4	4	4	4	4	4
CS/lot	100	100	700	700	4700	4700	32000
Samples	1	120	7	120	120	120	800
Seed Sampled	25g	3kg	175g	3kg	3kg	3kg	20kg
Probability	9%	99.9+%	50%	99.9+%	99.9+%	99.9+%	99.9+%

Table 11. Even small lots can be sampled with a high probability of capture if the seed is contaminated.

The Effectiveness of ISS Seed Screening is Inversely Related the Effectiveness of Chlorine.

The more contaminated the seed is, the less effective seed sanitizing is. Yet, the more contaminated the seed is, the easier it is to detect a pathogen using ISS' Seed Screening Procedures.

sprout_seed_screening

Figure 12. ISS Seed Screening is most effective when the seed is heavily contaminated, which is when sanitation is least effective.

If we compare two lots of seed; one with 1,000 contaminated seeds and one with 10,000 contaminated seeds. In order to have a complete kill on the first lot, you have to kill the pathogens from 1,000 seeds. In the second lot, you have to kill those same pathogens from 1,000 seeds, and kill the next 1,000 contaminated seeds, and the next and next until you have killed 10 times as many pathogens as the first group. So chlorine has better odds of effectively sanitizing the 1,000 contaminated seeds than the 10,000 contaminated seeds.

On the other hand, seed sampling has a 63.2% chance of capturing a contaminated seed in the first lot, and a 99.9% chance in the second lot if the contamination is distributed evenly in the contaminated bags.

Seed screening along with decontamination complement each other to reduce the risk of salmonella or E.coli 0157:H7 in sprouted seed.

Don't All Seed Companies Follow These Procedures?

ISS developed this program, and appears to be the only company in the world who does this extensive testing.

Some seed companies will take a handful of seed from a bag and send it to a lab for pathogen testing. The lab will take 20-grams (less than an ounce) from the sample and test it for pathogens. Yet in previous outbreaks in which contaminated seed was recovered the contamination levels have been as low as 2 pathogens per pound of seed (4cfu/kg).

What do you think the likelihood of finding those two pathogens is when testing less than an ounce of seed? It is less than 8%.

So why do labs only test 20-25 grams? They do not have commercial sprout equipment! And what are they going to do with the 360 lbs (163 kg.) of sprouts produced from a 36 pound sample of seed?

So is ISS Proposing That Sprout Growers Don't Need to Sanitize their Seed or Post-Test for Pathogens?

Far from it, but if seed companies had been selling seed that was not contaminated, the sprout industry would not be in the situation it is. The FDA would not be alarmed at all, and sprouts might actually be considered one of the safest products in the produce department.

That is water over the dam, and it will take many years of no outbreaks before sprouts are considered a safe product again. But because pathogens can be internalized in seed or protected in biofilms on sprouts, the sprout industry cannot count on sanitization alone. The best solution is to start with seed that is well screened and to verify through post testing that the seed screening and sanitizing was effective.

What are the Weaknesses of Seed Screening?

The probability chart above is based on the probability of capturing a contaminated seed. But once captured, the pathogen needs to be detected. As of this date, no test for salmonella or E.coli O157:H7 is perfect. According to the papers highlighted in the previous sentence, the best one can expect from a test kit is detecting contamination 97% of the time it is present in a sample. To overcome this shortcoming, the water samples need to be tested in duplicate, which brings the probability of detection closer to the probability of capture.

Similar to the ISS' Seed Sampling, the probability that at least one of the duplicates is positive is greater than the probability of a single test being positive (given that the pathogen/organism is present). So, if a pathogen test has a sensitivity of 97% (i.e. probability of a positive test given the sample is positive) then a testing scheme utilizing duplicates should have an overall sensitivity of 1 - (1-0.97)^2 = 0.9991 - which, is virtually 100%.

A weakness of the ISS Seed Screening Program is the possibility of basing decisions on inaccurate information. You are forced to rely on seed lot information provided by other people. A seed lot is supposed to be one uniform lot. Suppose someone along the line, farmer, seed processor, seed supplier, etc, retags seed. The reliability of the information provided by the test would be lower than the probability charts. For instance, if you purchase 800 bags of lot A, and a seed supplier decided they could get rid of the last 30 bags of lot B, the last 18 bags of lot C, and the last 2 bags of lot D by retagging them all as lot A. Your test may still be quite accurate for the 750 bags that originally made up lot A, but not very reliable for the fifty bags that made up lots B, C, and D. Although this marginalizes seed screening, it would have still been effective on 750 bags, which is 94% of the lot and therefore still a useful risk reduction step.

Probabilities of detection require knowledge of the quantity and distribution of pathogens in the particular seed lot. This information is not known, so actual probabilities cannot be predicted. However, sampling on some seed lots that have been implicated in outbreaks has been able to isolate pathogens, which strongly suggests that if this sampling had been done beforehand, the seed would have been diverted to non-food uses, and the outbreak would not have occurred.

ISS Seed Screening Does Not do the Following Things:

It does not cost much.
It does not produce hazardous wastes.
It does not put production workers at risk.
It does not effect germination, vigor, yield, or the quality of the sprouts.
It does not reduce background flora.
It does not introduce the possibility of resistance.
It does not disenfranchise organic sprout growers.
It does not negatively affect or take away from other food safety procedures, such as decontamination.

What ISS Seed Screening Does:

It helps the seed industry identify practices that introduce pathogens into foods.
It can prevent contaminated blended lots from entering the market if sampling is done prior to blending.
It can prevent some seed with visible contamination from entering the market. This includes glass and other things that would not show up on a pathogen test.
It is most effective when sanitizers are least effective.
It helps identify farms and seed processors lacking Good Agricultural Practices.
It is used identically on all types of seed.
It affects commercial sprout growers of all sizes, with all levels of sophistication and using all types of equipment. It can be applied evenly throughout the sprout industry.
It can be used on seed destined for home sprouters, and may be the only realistic defense that home sprouters have. Chlorine is not a very good option for home sprouters.
It shifts some of the responsibility of providing safe seed to the seed industry itself.
It has substantially reduced the number of food borne illnesses from sprouts. (Currently at zero for all sprouts produced from seed screened using this protocol. It is only a risk reduction step though. Seat belts reduce the risk of injury in traffic accidents, but people still get hurt. So just because this seed screening program has a perfect record regarding outbreaks, it is just a method of reducing risk, not eliminating it. We screen millions of pounds of seed a year. At some time, contaminated seed will get through undetected, and an outbreak will occur. Just not yet. )

Who Should Do These Procedures?

It is the growers who are ultimately responsible for producing safe sprouted products. They can do these procedures themselves, they can get screened sprouting seed from International Specialty Supply, or they can do both. The more the seed is sampled and tested, the less likely it is to be contaminated. No matter who does it, the grower needs to have good documentation of exactly what was done, when it was done, and who did it. Without this documentation, growers (and health inspectors) need to consider the seed unscreened and unsafe.

These procedures do not eliminate or reduce pathogens in the seed. If seed is contaminated before it is screened, it will still be contaminated after it is screened. The procedures reduce the risk that the seed may contain the human pathogens that they were screened for. If International Specialty Supply does these procedures, it does not guarantee that there are no pathogens in the seed. It does guarantee that ISS did everything it signed off on in writing for a particular lot of seed. Once the seed is properly sampled, inspected and tested, a document is signed by ISS making it "ISS Screened Sprouting Seed".

These tests are extensive and vary from seed to seed and lot-to-lot. ISS cannot practically test every lot in every instance. Drop shipments, for example, are almost never tested. With rare exception, all of the seed that comes into ISS’ warehouses in Tennessee and California are tested. But the only way to know for sure is to receive the documentation from us for the particular lot of seed you are interested in purchasing.

ISS strongly encourages growers to get the safety documentation regarding each lot of seed they purchase. A copy of ISS’ documentation is attached. A copy of the ISS Seed Sampling and Testing Flow Chart and its Seed HACCP plan are available upon request. A copy of the ISS Seed Screening Documentation is available by pressing the navigation bar at the top of this page.

Who Else Believes in the ISS Seed Screening?

The FDA invited ISS to present their seed screening procedures at the five year meeting in May, 2005. The FDA will very likely adopt ISS' seed screening procedures as recommendations for all seed sold as sprouting seed.

The FDA has advocated the "Six-step procedure developed by ISS" in numerous reports and presentations.

In his keynote address to the June 9, 2009 Scientific Session of the ISGA Convention in Chicago Dr. Martin Cole (Chairman of the International Commission on Microbiological Specifications for Foods (ICMSF) and Director, National Center for Food Safety and Technology (NCFST)), discussed the theoretical possibility that ISS Seed Screening protocol may be equivalent to a 2.34 log reduction or better.
The New South Wales Food Authority implemented seed screening in their Plant Products Safety Manual and noted that "The seed pre-screening sampling process is based on the method developed by International Specialty Supply of Cookeville. TN, USA and Jonathon Sprouts of Marion, MA USA. www.sproutnet.com/sprouting_seed_safety.htm." (Pages 28, 31 and 33) Its applicability to Australian conditions was reviewed and confirmed by the South Australian Research and Development Institute.
The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), adopted ISS' seed screening program as recommendations for seed companies and sprouters in its "Sprouted Seeds Good Manufactures Guidebook." 2007.
- "Using similar testing methods, other seed suppliers should also be able to supply safe seed."
The World Health Organization
- "Outbreak investigations have indicated that microorganisms found on sprouts most likely originate from the seeds"
- "There is currently no treatment available that can guarantee pathogen free seeds."
- "Seed producers, distributors, and sprout producers should test lots of seeds for microbial pathogens"
- "Sprouting seeds before testing increases the possibility of finding pathogens that may be present. If lots of seeds are found to be contaminated, they should not be sold or used for the production of sprouts for human consumption."
- "Failure to find contamination does not guarantee that the seeds are pathogen free. However, if contamination is found at this stage, it allows seeds to be diverted or destroyed before entering sprout production for human consumption."
- Codex Alimentarius
  5.2.3.1 Testing of seed lots before entering production

• The seed sample selected for testing should be sprouted prior to analysis to increase the potential to detect pathogens if present. Analysis may be performed on the sprouted seeds or the water used to sprout the sample.

• Seed samples for microbial analysis should not be subject to any microbiological decontamination treatment at the sprouting facility.

The Center for Science in the Public Interest advised the FDA:

[ISS] “…has demonstrated that seed screening has many benefits and is very inexpensive. FDA should mandate that seed distributors conduct this kind of screening and certify their seeds as safe [Actually, ISS certifies them as being screened], in order to [help] prevent contaminated seed lots from entering the market. This could significantly reduce the number of outbreaks associated with sprouts.”

Resources For the Future, a Washington DC based think-tank, in its seminar titled "Achieving A Safe Food Supply in Increasingly Global Markets" wrote:

[ISS] "developed a program of seed screening that has allowed it to avoid all sprout-related outbreaks or recalls in North America since 2000, causing health organizations worldwide to start recommending ISS screening procedures be used on any seed destined for sprouting."

FSA (Food Standards Agency, UK)

"Outbreak data indicate that the seed used for sprouting is the most significant source of the pathogens implicated. …bacteria that are trapped in cracks and crevices in the seed coat appear to be protected from disinfectants and there is evidence that some bacteria can be internalized within the seed itself......to date no technique has been shown to completely eradicate pathogenic micro-organisms from either the raw or sprouted seed...Given the difficulty of decontaminating seed another important aspect ...is the detection and isolation of pathogens from the seeds used to produce sprouts."

The Campden Research Group in England in their 2004 report titled “Review of microbiological risks associated with sprouted seeds” concluded that

“Absence of pathogens in seeds is critical and, consequently, microbiological testing of seeds prior to use for production of sprouts is essential.”

Seed sampling is also suggested in the Codes of Practice for Food Safety in Ireland.

“As seeds are thought to be the most likely source of contamination…The dried seed should be sampled and tested microbiologically upon arrival. Seed contamination is thought to be sporadic, at low levels or unequally distributed throughout seed lots. Therefore, a negative result does not guarantee the absence of pathogens; however a positive result allows a producer to avoid using contaminated seed lots.”

Leading researchers for the USDA and FDA, William F. Fett, Tong-Jen Fu, and Mary Lou Tortorello in "Seed Sprouts, the State of Microbiological Safety" Chapter 6 of Microbiology of Fresh Produce, Edited by Karl R. Mathews, 2006 pp202-207.

“Proper sampling inspection and testing of seeds for pathogens can substantially reduce the chance of using contaminated seeds for sprout production and therefore help prevent foodborne illness. However, improper seed screening protocols may still result in outbreaks."
"A comprehensive seed sampling and testing procedure has been developed [ISS]." Then they explain ISS' process described above and close with: “The adoption of these seed-screening procedures has already prevented at least four potential sprout-related outbreaks do to Salmonella and E.coli O157:H7.”

Food Safety Researcher and Professor Keith Warriner "Interventions to Improve Food Safety of Sprouted Seeds" in his PowerPoint Presentation for British Columbia's Premier Food Safety Conference - October 18, 2007.

The California Department of Public Health highly recommends sampling in their Advisory to Commercial Sprout Producers, May 1, 2008 (Comment #2). Their advice is based on ISS' seed screening program.

Trevor Suslow, Plant Sciences and Postharvest Technologist, UC Davis, In his presentation titled "Evaluating Seed Borne Pathogens as a Risk Factor in Produce Outbreaks" for the Plant Disease Seminar, Nov, 13, 2007 concluded his presentation with "Recommendations for Seed Industry GAPs & BMP’s - “Most critically, before engaging in any seed testing program, a uniform and standardized test procedure must be determined. Statistically sound sampling protocols need to be established...The experience of the sprout seed industry with pathogen-free certification programs can provide insight into approaches and problems (SproutNet has valuable and practical information on testing programs and access to abstracts of published seed food safety research)." Trever Suslow

In the study “Factors Influencing the Growth of Salmonella during Sprouting of Naturally Contaminated Alfalfa Seeds” FDA and National Center for Food Safety and Technology researchers referenced the ISS Seed Screening Program when they point out that "To prevent the consumption of contaminated sprouts, the absence of pathogens in seeds must be assured. Screening of seeds by seed suppliers for the presence of pathogens can help to reduce the number of contaminated seeds entering the marketplace."

NOTHING ELIMINATES RISK: ISS Seed Screening or the use of ISS Sprouting Seed is one of several methods that should be employed by commercial sprout producers to reduce the risk of human pathogens in sprouts. Seed should also be properly sanitized prior to production and the sprout run-off water should be tested for human pathogens between 24 and 48 hours of production.

For more information on seed sampling and testing see "Seed Sampling and Testing: A risk-reduction strategy for sprouts."

Produce Outbreaks

1990-2002

Vegetables

Fruit