Building A Better Understanding Of Salmonella In
Source of Article:
In the course of our coverage of the
we’ve confirmed what we have found in previous outbreaks: The FDA has no
one with deep expertise in these commodities.
Sometimes the failure shows up in terms
of not understanding the industry and distribution systems; sometimes it
shows up in terms of not really understanding the commodity itself.
Because the recent pistachio recall has
left so many open questions, we turned to Linda Harris at the University of
California at Davis. We spoke to many experts and all identified her as the
person to speak to when it came to tree nuts. She is understandably busy
just now, but was kind enough to work with Pundit Investigator and Special
Projects Editor Mira Slott to fill in some of the gaps in industry
understanding of the intersection between Salmonella and pistachios:
Linda J. Harris,
Western Institute for Food Safety and Security
Cooperative Extension Specialist in
Microbial Food Safety
Department of Food Science and Technology
University of California
Q: Where do pistachios rank in terms of
risk for contamination of Salmonella in comparison to other produce items?
Are pistachios a common or uncommon host for Salmonella? Why or why
not? Do different nuts, such as peanuts or almonds, pose higher or
lower risks of Salmonella contamination?
A. There is relatively little information
available on Salmonella in nuts. The largest body of work relates to
almonds, with some early work about 30 years ago on pecans, a little
recently on peanut butter and a few, relatively limited international
prevalence studies. And that is it. So your questions simply
cannot be answered. There is no data to compare risks among nuts.
Q: What is required in the processing
stages to provide a kill step and eliminate any potential pathogens in
pistachios? Does roasting act as a kill step? What needs to occur,
i.e., reach a certain temperature for a particular time period, for
example? What other methods would work as kill steps? What types of
research is being done in this area?
A. Thermal (heat) processes are the most
common applied to foods. Typically we think of a heat process in terms of a
given time at a certain temperature. The basis of validated thermal
processes is that this time and temperature combination will result in a
certain predictable reduction of target microorganisms. In general,
the greater the time at a given temperature, the more microbes you kill AND
less time is required at a higher temperature to kill the same number of
microorganisms. Most processes that are designed to kill pathogens
target the most heat resistant pathogen that would be important for that
A reduction goal is also set (for
example: 10,000-, 100,000-, 10,000,000-fold reduction — these are 4-, 5-
and 7-log reductions). “Eliminate” is not a term used by regulators or
microbiologists – we say “reduce to an acceptable level”. That
acceptable level often can be considered “virtually eliminate,” but it
isn’t scientifically correct to say eliminate.
Thermal processes for nuts include oil
roasting, dry roasting, and blanching as more traditional practices, but
heat can also be applied through steam, infrared heat, etc. Each nut
type has different handling after harvest, and there is variability in the
type and amount of heat that is/can be applied. There are also other
treatments such as gas (propylene oxide).
We are all pretty familiar with
temperatures that are given for cooking poultry and other meats. The
USDA recommends cooking turkey to 165
degrees F. This guidance is designed to reduce Salmonella by
10 million-fold (7 log). The meat industry must follow validated
guidelines for cooking roast beef. In this case, achieving a
temperature of 158 degrees F is sufficient to reduce Salmonella by
10-million fold — the target set for this product.
The time (or the time/temperature combination) is zero seconds for
these two examples. For the roast, if you look at the USDA chart you can
see that an equivalent reduction is achieved at lower temperatures in
combination with longer times.
I understand why people might assume that
these types of times/temperatures should be adequate for other types of
foods such as nuts. However, this is one of the most common misconceptions about
Salmonella. Meat and poultry are moist. Once Salmonella dries
as it would be on a nut it becomes remarkably heat resistant. If we
look at some of the validated processes for almonds — oil roasting requires
2 minutes at 260 degrees F to achieve a 100,000-fold reduction of
Salmonella (5 log) — 100-fold less reduction than in the roast beef or
turkey examples — yet we had to use 100 degrees F higher temperature and 2
extra minutes to achieve this. Even blanched nuts need to be exposed
to hot water for 2 minutes at 190 degrees F to achieve a 100,000-fold
reduction, which is much longer time and higher temperature than for turkey
[Note: Domestic almonds must be
treated using a process validated to achieve at least 10,000-fold
(Editor’s note: you can read the Pundit’s
coverage of the almond situation here
A second complication is that not all
heating methods are equal. That is clear in my example above — there
is a very large difference between heating in hot oil (260 degrees F) and
hot water (190degrees F) to achieve the same reduction of Salmonella in 2 minutes.
We do not currently know if the data for almonds and oil roasting or
blanching apply to other nuts.
When we move to dry roasting, things get
really complex. Each type of dry roaster has a different heating
profile. In addition, many dry roasters do not achieve uniform
heating across the roaster. Data generated for oil roasting is not at
all applicable to dry roasters, and each dry roaster must be individually
For pistachios, dry roasting is most
commonly used. Different companies will not only have different
pieces of equipment but they may also have different times/temperatures
that they use to achieve a certain end product quality. Validation of dry
roasters is ongoing in the pistachio industry at the moment. Each
company will be generating their own data for each roaster or roaster
type. Most will probably hire a “thermal process authority” to do
this as it is not an easy task, and it requires someone with expertise and
experience with these types of validations.
Q. If raw pistachios carrying Salmonella
were entering the processing plant, how likely would it be during periodic
environmental testing within the plant where raw product was being handled
during the processing stages for samples to test positive for Salmonella?
A. There is no answer to this
question. There simply is no data.
Q: What is the significance of FDA
discovering Salmonella in the Setton processing plant? Wouldn’t it be
important to know exactly where the samples testing positive were taken in
terms of the processing flow to make a meaningful assessment?
A: This demonstrates the presence of
Salmonella in the processing facility. [Editors note: more on its relevance below] It
would be useful to know this information but not critical at this point.
Q. What is the statistical/scientific
significance that the Montevideo variety of Salmonella was discovered at
the Setton plant in April and also in Georgia Nut Company’s testing of
Setton product back in March? How scientifically significant is it that the
same PFGE pattern of the Montevideo strain was discovered at both the
Setton plant in April and also in the Georgia Nut Company’s testing of
A. There are many different serovars of
Salmonella. Montevideo is not uncommon but there are multiple PFGE
patterns for this serovar. Finding a PFGE match between isolates from
a finished product and the facility that produced the product provide
further evidence that the two are linked. The fact that the organism
is still in the processing facility indicates that it has been there for
some time. In the 2000/2001 raw almond outbreak, investigators found
the outbreak strain in the processing facility several months after the
outbreak-associated lot was processed. It was also found at the
huller/sheller and in the orchard. So we know that Salmonella strains
can “hang out” in processing facilities and other environments.
Q. FDA said that four different strains
of Salmonella (including Montevideo) were discovered in the Georgia Nut
Company’s testing of Setton product in March. How common would it be to
find four different strains of Salmonella in the same round of testing?
A. It depends. It would not be
uncommon to find more than one type of Salmonella in a food product upon
Q. Is it notable or inconsequential that
the other three strains were not found during extensive testing at the
A. It is inconsequential.
Q. Is it notable or odd that Setton
Pistachio had received excellent food safety ratings during regular audits
from numerous reputable companies, and no one pointed out any violations of
A. There are a group of food
microbiologists and food safety specialist that have been talking about the
importance of Salmonella in dried foods for a long time.
Unfortunately, the dogma has been that dried foods are not an issue for
foodborne illness so not everyone paid attention to us.
A: More misconceptions:
1. Salmonella can’t grow in dried
foods so they aren’t a problem. Actually it is true that Salmonella
cannot grow in a food that is dried below a certain moisture level.
However, they do survive on dried foods for very, very long periods of
time. When the dried food is cooled down to refrigerated or freezer
temperatures Salmonella levels will remain constant for years (another
difficult concept for many people).
2. High levels of Salmonella are
needed to cause illness. Not true. There are a number of
outbreaks in dry foods where levels of Salmonella were documented and very
low levels (10 cells or less per serving) were sufficient to cause
illness. Salmonella doesn’t need to be able to multiply to cause
If you couple these misconceptions with
the “any kind of roasting will always eliminate Salmonella,” you can
imagine that inspections/views of processing facilities for these products
might have been inadequate from the perspective of Salmonella
contamination. They weren’t looking for potential sources of
Salmonella or for validated kill steps or for potential cross contamination
It is my hope that in 2009 we finally
have enough evidence to convince the dried food industry that Salmonella IS
an issue they should address – ALL DRIED FOODS - regardless of whether or
not Salmonella has been isolated from the product and regardless of whether
there has been a documented outbreak. RE-EVALUATE your safety
programs with the view that Salmonella IS a potential hazard – that may
just ensure it never is.
Q. This pistachio recall is massive. Does
the size of the recall of Setton products seem weighted appropriately to
the potential risk? What scientific methods can be employed to determine
the size of a recall?
A. I have not seen the data that FDA and
Setton Farms used to determine the scope of the recall. I will say
that recalls can be more limited in scope if the company has data to
support that the contamination is limited to one or more well-defined lots.
Q. Could recalled pistachio products be
sent out for re-roasting and safely be sold in the market?
A. Products can be “reconditioned” if
they are processed with a validated kill step and they are protected from
re-contamination after that kill step.
Q. What additional actions can pistachio
companies take to alleviate the risk of Salmonella contamination?
A. As I said earlier — this applies to
all dried foods. The new GMA Salmonella control guidance and appendix
should be mandatory reading for all in the dried food business. I
have begun to compile nut-related information at this site including the
There are many things that can be done.
I think the GMA document covers the basics very well, and I have
taken a section out of that document table of contents that covers all the
points I would make:
SALMONELLA CONTROL ELEMENTS
1. Prevent ingress or spread of
Salmonella in the processing facility
2. Enhance the stringency of hygiene
practices and controls in the Primary Salmonella Control Area
3. Apply hygienic design principles to
building and equipment design
4. Prevent or minimize growth of
Salmonella within the facility
5. Establish a raw materials/ingredients
6. Validate control measures to
7. Establish procedures for verification
of Salmonella controls and corrective actions
We really are in debt to Linda Harris.
She has clarified issues that hundreds of articles and countless
interactions with government authorities have been unable to clarify. Here
are the seven big points we take from this:
1. There is insufficient data. We need to
get the various tree nut producers to start funding studies. Perhaps The
Center for Produce Safety, all set up and operating, could extend a hand of
outreach to the tree nut communities and offer to facilitate the research
if the tree nut folks will fund it. We need to understand baselines,
comparative risk, to know when we are experiencing the norm and when it is
an exception. We need good, hard, scientific data. Which means we need
2. If you are going to use roasting as a
kill step then every type of roaster must be individually validated. We
don’t actually know if a particular type of roasting is a kill step or not
unless it is validated.
3. Almonds have had more trouble and so
have come to require a treatment validated to achieve a 10,000 log
reduction. One possibility is that most of the roasters are already
achieving this and so problems have been few on pistachios and we need a
formal validation procedure to make sure no one errant roaster is causing a
problem. More research in the field might tell us if Salmonella is more or
less prevalent on the raw pistachios than it is on raw almonds.
4. We think it fascinating that Dr.
Harris does not think, at this point, it is critical to know where in the
processing plant Salmonella was found. The FDA and CDFA have not even
attempted to trace the Salmonella back to the trees. They assume there is
Salmonella on the raw nuts and count on the assumed kill step — roasting —
to make the product acceptably safe. So the FDA and CDFA seem to be
accepting that the plant will take in Salmonella laced product, which means
they would expect to find Salmonella in intake areas and other parts of the
plant prior to roasting. It seems Dr. Harris has different expectations.
We asked Dr. Harris if she thought the
FDA and CDFA should go back to the fields as they did in the spinach crisis
and she gave this answer:
I think you are
trying to compare two very different things. In the case of the
spinach outbreak — it was outbreak #20 associated with lettuce and leafy
greens if I remember correctly. There was strong incentive to attempt
to identify a source of the organism with the goal of potentially
preventing future outbreaks. In addition, their traceback was able to
narrow the investigation to 4 farms (I am going from memory on the number
of farms) which helped improve the odds that they might actually find
In the almond
outbreak in 2000/2001 they were able to identify the processor through
microbial sampling, they narrowed the lot to 4 huller/shellers and then
found the outbreak isolate at a single huller/sheller and were able to
focus the “field” work on three farms (and they were able to isolate the
organism from the orchards on those farms).
In both cases
there was an outbreak. Both investigations involved huge input in
terms of human resources and sample analysis even with the targeted
analysis of a few farms. In many ways these types of investigations
are needle in a hay stack and you really need to keep them as focused as
possible so that you don’t spend a lot of money for zero results.
In this case I am
not sure it is good use of limited state or federal resources to push this
back further. Also, it may not be possible to narrow the
investigation to a small number of farms or orchards at this point in time
or given the records available.
Obviously resource allocation is always
an issue but we would point out that this is not what the FDA and CDFA
claimed when we spoke to them. We were told that the distinction had to do
with the fact that spinach is consumed raw, without going through a kill
step — so no pathogen is acceptable. In the case of pistachios, we were
specifically told that the government assumes there is Salmonella on raw
nuts and so doing trace back would not yield any important information.