International Specialty Supply
Supplying Sprout Companies Throughout the World
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International Specialty Supply Supplying Sprout Companies Throughout the World
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820 East 20th Street Cookeville, TN 38501 USA 931 526 1106
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Another
Grower Prevents an Outbreak
Sproutnet International Specialty Supply November 12, 2001 We
received a call from a grower on the US East Coast who had a confirmed
positive for Salmonella. His test was done at 48 hours and was a composite
of water taken from three Rota-Techs. Alfalfa, broccoli and cabbage
sprouts were being produced in those drums. He just used up his
next to last bag of alfalfa. He had been using the broccoli for a
couple months and the cabbage for a year. He bought his alfalfa seed from ISS,
and we had sampled every bag and tested it for pathogens using the
sprout production method. He bought his cabbage and broccoli seed from
another supplier who said they "tested it" but didn't describe how and
provided no documentation. The grower sanitizes his seed using the
20,000-ppm calcium hypochlorite. He was using the hold and release program
recommended by the FDA, so no product had left his building. We may
never know if the salmonella came from the seed, a person, or the
environment. For sake of discussion let's assume that it came from the
seed. But if it came from the seed, which seed did it come from? If the
lot of seed was quite contaminated, it probably came from the broccoli or
cabbage. If it were in the alfalfa, it probably would have been detected
when each bag of the entire lot of 880 bags were sampled and tested by ISS.
If the
contamination were localized to one bag of seed, it could have been the
broccoli, cabbage, or alfalfa. If there is light contamination, say, 4 contaminated
seeds per kilogram, the odds of finding it if it is only in one bag is
only 9.5% (by taking a 25 gram sample). It needs to be in 7 bags to
increase the odds of capture (for detection) to 50%, and in 47 bags to
increase the probability of capture to 99%. So when you are testing
880 bags, it only needs to be in 5% of the bags, at low levels, to get
a 99% probability of capture. In
order to have a 50% probability of capture in one bag the seed would
need to be contaminated at the rate of 28 seeds per kilogram, and in order
increase to probability of capture in one bag to 99% there would need to be 185
contaminated seeds per kilogram, or about 1 in every 2,700 seeds. The
other alternative is to increase the sample size from 25 grams per bag to 175
grams. In
other words, if only a few bags of a lot are lightly contaminated, there is no
reliable way of detecting it other than testing larger quantities of seed.
This is impractical for most seed companies because the seed is not usable after
it is tested. This
means that even though seed has been properly sampled and tested for pathogens,
there may be times when it escapes detection. If it is contaminated,
it is likely to be either extremely lightly contaminated (one contaminated
seed per 4 bags) or have light contamination localized in a few bags. The
chlorine kill step would probably be effective against the extremely lightly
contaminated seeds. If it is localized to one bag, then fortunately the
other 879 bags are not contaminated so there would not be a major outbreak.
Just like sanitizing or post testing, the system is not perfect, but it is
a very important risk reduction step. In
the case of the seed used by the grower who prevented the outbreak, he does not
know which seed contained the pathogen. If the contamination came from the
broccoli or cabbage, the industry may have a major problem. If it came
from the alfalfa seed, it probably doesn't. |