Monday, April 4, 2011

Apple #516: Bagged Salads and Bacteria

A regular Daily Apple reader, Anonymous California Guy, recently asked me if he should wash his bagged salads before eating them. He said normally he doesn't, but he read a Consumer Reports article that said they found bacteria in several samples of bagged salads.  He wants to know, does he really have to wash those salads and dry them and wrap them in towels in the fridge before eating?

Ah, the pre-washed and bagged lettuce.  Are we paying more than just extra money for that lovely convenience?
(Photo from Trudi Pratt's blog)

My initial and admittedly uninformed reaction to this is that we have been eating lettuce and spinach and all sorts of leafy things for CENTURIES.  Our food safety is probably better than it has ever been, as is probably our public health.  And yet we keep getting freaked out by the possibility of bacteria in our food.  I have a very strong suspicion that there's always been bacteria in our food.  Most of the time our body deals with it just fine and we never know about it.  Sometimes it makes us sick and we deal with that.  There are also some bacteria that are even good for us.  So my personal reaction to this news is, eh.  Big deal.

But ultimately the question to the Apple Lady (yes, she's an alter ego) becomes who is right: me or Consumer Reports?

First of all, here's what Consumer Reports did:
  • They inspected 208 containers of pre-washed salads. Some packages were in bags, some were in plastic clamshells.  
  • They bought the salads at stores in Connecticut, New Jersey, and New York.  The samples were from national brands like Dole, Fresh Express, and Earthbound Farm Organic, as well as regional and store brands.
  • All the samples were within their use-by-date, though some were older than others.
  • Their findings: 39 percent (that's 81 packages) tested positive for 10,000 or more colony-forming units per gram of total coliforms. 23 percent (that's about 48 bags) tested positive for similar levels of enterococcus.

So what should I do?

I'll answer this first according to what Consumer Reports recommends.  Then I'll get back to my take on it later.

  • The Consumer Reports study says that more of the packages that tested positive for these bacteria were the ones that contained spinach.  They don't suggest that you should avoid or specially wash the ones with spinach, but something like that seems to be the implication.
  • They also noticed that the majority of the bags that tested positive for these bacteria were ones that were closer to their use-by-date.  So they suggest that people buy the packages that are marked with use-by-dates that are as far in the future as possible.
  • They also recommend that even if the bag says the greens have been been washed once or twice or however many times that you should wash them again. 

What does it really mean?
  • First of all, the Consumer Reports study's sample size is small.  They say as much themselves.  208 samples is a pittance.  By comparison, in 2008, the Department of Agriculture tested more than 4,000 samples of both loose and packaged salad.
  • Second, the Consumer Reports sample size is localized to one region of the country.  Yes, some of the bags were from national brands, but many of the others were regional or local.  You can't say for certain that the prevalence of bacteria is at the same levels elsewhere in the country.  They may even be higher than what Consumer Reports found, but you can't say that for certain.
  • What a lot of people leave out when they re-report this story is what Consumer Reports didn't find.  They didn't find any of the worst offenders.  They found no E. coli (specifically, no E. coli 0157:H7, which is the strain that is particularly virulent), no listeria, and no salmonella.
  • (By the way, that 2008 at Department of Ag study that tested 4,000 samples? They found salmonella in two.  That's .05%.  AKA not statistically significant.  Yeah, I know, tell that to your stomach when you're throwing up, but that .05% lightning is not likely to strike you.)
  • Finally, just what are total coliform and enterococcus?  Let's take up total coliform first.  
Coliform bacteria are organisms that are present in the environment and in the feces of all warm-blooded animals and humans. Coliform bacteria will not likely cause illness. However, their presence in drinking water indicates that disease-causing organisms (pathogens) could be [present.]
The total coliform group is a large collection of different kinds of bacteria. Total coliform bacteria are commonly found in the environment (e.g., soil or vegetation) and are generally harmless. If only total coliform bacteria are detected, the source is probably environmental. Fecal contamination is not likely.
Fecal coliform bacteria are a sub-group of total coliform bacteria. They appear in great quantities in the intestines and feces of people and animals. E. coli is a sub-group of fecal coliform. The presence of fecal coliform in a sample often indicates recent fecal contamination meaning that there is a greater risk that pathogens are present than if only total coliform bacteria is detected.
  • The Consumer Reports study didn't mention fecal coliform bacteria.  They said they looked for total coliform bacteria.  They also said specifically that they did not find any E. coli, specifically the strain that is the really bad one.
  • One other thing to note about total coliform bacteria.  Since it's not feasible to test every type of food for every possible bacteria, they test for total coliform as a way to get a sort of bellwether on what's going on.  It doesn't tell you anything for sure about what's going on in there, but it gives you an indicator of what may be happening.
  • So the total coliform that Consumer Reports did find may indicate the possibility that fecal contamination occurred and that other pathogens therefore may possibly be present.  
  • So it's especially worth noting again that in this case, they did test for the three especially bad pathogens and those were not present.  Even in those samples that had the total coliform bacteria, the total coliform didn't turn out to be accurate indicators of the presence of other pathogens after all.
  • Now let's talk about enterococcus.
  • Enterococci are another group of bacteria, this one even more diverse.  Some enterococci are actually beneficial.  They are used to ripen cheeses and sausages.  Some are even sold as probiotics (ah, that's a hot buzzword these days).  They're incredibly prevalent.  They can be found in the soil, in the water, and in food.
  • Some enterococci -- particularly the ones that are associated with feces -- are pathogens of "relatively low virulence" that cause illness.  Some strains of these bad enterococci have developed resistance to antibiotics.
  • The bad enterococci can do some bad stuff.  Mostly it makes people throw up or it gives them diarrhea, both of which are your body's natural and desirable method of hitting the eject button.  More rarely the bad enteroccoci can cause urinary tract infections, meningitis, tissue ulcers, all sorts of stuff you really don't want.
  • So, yeah, maybe it's a bit worrisome that they found some enterococcus in there.  But the Consumer Reports article doesn't say which enterococcus they tested for.  Since their goal was to determine food safety and sanitary levels, it's probably a good assumption that they were testing for the fecal sort.  But that's only an assumption.  They could have been testing for the lot of enterococci as far as I know.
  • In all, 48 bags out of 208 had some kind of enterococcus, which may or may not be the bad kind. That's about 1 in 4.

Odds are, 1 in 4 of these bags of pre-washed lettuce have some form of bacteria, the exact strain of which may or may not be harmful.
(Photo from babble)

If you don't like those odds, here's what you can do to try to improve them:
  • Buy the freshest package available.
  • Once you've got them home, rinse the greens again yourself.
  • Take them out of the bag in which they were sold, rinse them in cold running water, and pat them dry.
  • Use them immediately, or if you need to store them for a while, put them in a different bag, one that's clean and hasn't been used to store anything else.
  • Keep them in the refrigerator.  Bacteria don't grow as well in the cold.
  • Eat them as soon as possible.

But even all these precautions are no guarantee.  As the Consumer Reports article itself points out, "Rinsing won't remove all bacteria but may remove residual soil."

My summation: you pays your money and you takes your chances.  Same as in every other freakin' thing in life.

(Photo from iNet Giant)

Consumer Reports, Bagged salad: How clean? March 2010
CBSNews, How Clean Is Your Pre-Washed Salad? February 2, 2010
Elaine Magee, WebMD Healthy Recipe Doctor, Bagged Salad and Bacteria: What YOU Can Do, February 3, 2010
Sarah Jio, Do You Wash Your Bagged Lettuce and Salad Mixes Before Using Them? Shine on Yahoo!, February 3, 2010
Washington State Department of Health, Division of Environmental Health, Office of Drinking Water, Coliform Bacteria and Drinking Water
Cornell Agricultural Experiment Station, Food Safety and You: Coliform Bacteria as Indicators of Food Sanitary Quality, 1999
Wilhelm H. Holzapfel, Enterococci in foods--a conundrum for food safety (Abstract), International Journal of Food Microbiology, December 2003

1 comment:

  1. Hey Apple Lady,
    Anonymous California Guy


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