I eat a lot of salad. Not because I think they are healthy but because I like salads. When I go to lunch at the hospital cafeteria I usually eat from the salad bar, and believe me, that's not a pro-health measure. You'd know what I mean if you saw the salad bar. But green leafies are supposed to be good for us, too, so that's a bonus. But a new study from CDC suggests that they are not quite as healthy as they once were:
Over the past 35 years the proportion of foodborne outbreaks linked to the consumption of leafy green vegetables has substantially increased and that increase can not be completely attributed to Americans eating more salads according to research presented March 17 at the 2008 International Conference on Emerging Infectious Diseases in Atlanta, Georgia.[snip]
Prompted by the high profile E. coli outbreaks associated with spinach and lettuce in 2006, [CDC's Michael Lynch] and his colleagues decided to investigate the incidence of foodborne disease outbreaks associated with leafy greens in the past. Using data from the CDC foodborne disease outbreak surveillance system they analyzed over 10,000 foodborne disease outbreaks reported between 1973 and 2006.
For the entire period, approximately 5% of all foodborne outbreaks were linked to leafy greens. Most of these (60%) were caused by norovirus, but some were caused by salmonella (10%) and E. coli (9%).
[snip]
Using per capita availability of leafy greens in the United States as a proxy for leafy green consumption, the researchers compared per capita consumption of leafy greens with the proportion of foodborne outbreaks caused by leafy green consumption.
"During the 1986-1995 period U.S. leafy green consumption increased 17% from the previous decade. During the same period, the proportion of all foodborne disease outbreaks due to leafy greens increased 60%. Likewise during 1996-2005 leafy green consumption increased 9% and leafy green-associated outbreaks increased 39%," says Lynch. (Science Daily)
So it's not just that we are eating more green leafy vegetables. Nor is it likely to be how they are prepared. The size of the outbreaks suggests contamination early in a long process that results in widespread distribution. Now a lot of these vegetables are harvested far away, bagged and shipped long distances and finally wind up on a table, either in a restaurant or a home. The bag may say pre-washed but you would do well to always wash them -- thoroughly.
What really surprised me was the pathogens involved. The very high proportion of norovirus infections was stunning. I don't usually think of this as a foodborne infection but as a person to person or contact pathogen. But here they are coonstituting 60% of the identified agents for green leafy vegetables. It would be nice to know more about the environmental microbiology of this exceptionally nasty little hunk of RNA and protein.
Meanwhile I'll continue to eat salad. And try to buy local.
Medicine & Health
Comments
Note to self: Plant, tend, and harvest own lettuce this year.
Posted by: Anon | March 20, 2008 5:15 PM
Norovirus on lettuce, yikes! Another "who woulda thunk" from revere. Thanks, I think.
Local is great, but you already know to always wash your fruits and vegetables, even if the farmer is a nice person.
Posted by: tony | March 20, 2008 6:36 PM
We are buying a small farm when this property sells (btw you can say a wee small prayer it does sell soon for us. LOL) One of our goals is to raise both more crops and animals to sell to local restaurants. We have already had significant interest in local eateries wanting to buy my produce and eggs. There have been many articles in the local papers touting locally grown produce. What has been a hobby will now earn a little money.......at least that is the plan. Should be good for me, other small growers, local restaurants and as Revere suggests, other local consumers.
Posted by: Shannon | March 20, 2008 6:42 PM
During his preventive-med residency, my husband did a rotation with the local health department. They once tracked down a probable foodborne norovirus outbreak, and this kind of thing is a real pain to document because it doesn't follow the classic pattern of foodborne illness. For example: If someone leaves a pot of chili out too long at the church picnic, and it gets contaminated with pathogenic bacteria that can actually grow there, there'll probably be statistical support for a correlation between who ate the chili and who got sick. But, if careless food handling leaves norovirus particles on (say) the occasional piece of fruit in a cafeteria display, the viruses won't proliferate until ingested by a human. So, maybe one in ten of these items gets contaminated, and only a small percentage of the people who selected something from the fruit bowl will get sick. If the careless handling continues, customers will continue to come down with noro-crud, but it will be really difficult to associate it with the actual source.
I often wonder what we'd find if we looked closely at foodborne transmission of colds, flu, and other non-gastrointestinal viral infections.
Posted by: Julie Stahlhut | March 20, 2008 8:52 PM
Animal husbandry practices in conjunction with food farming is a bad combo all around. The best way to avoid many of these problems is to encourage a return to getting as much food from local harvests as possible, as well as breaking down the mass animal husbandry practices. (I'm not being anti meat by any means, but the way we do it now is killing not just the animals but us.)
Posted by: peanutbutter | March 20, 2008 9:30 PM
Julie: I think the door is still open on some of these other infectious diseases, although epidemiologically they don't behave like foodborne illness. Norovirus is remarkably difficult to do outbreak investigations on, so this surprise is only a surprise that it isn't more widely known as a foodborne agent. The CDC presentation (nothing published yet) seemed to indicate introduction higher in the chain than just prior to serving.
Posted by: revere | March 20, 2008 9:37 PM
Probably it has a lot to do with the ever-increasing practice of 'sludge spreading' on farmers fields - cheap or free fertilizer - barely treated human waste from municipal sewage systems - must be LOADED with pathogens!
Posted by: gharris | March 21, 2008 12:16 AM
Gharris,
It is against the law in every state to spread sludge on food crops. Anyone caught doing so gets a very hefty fine. The sludge is free to golf courses, tree farms, etc.... Also it has been treated to remove virtually all pathogens but, it does have heavy metal contamination as well as some pharmaceutical and chemical residues.
Posted by: Shannon | March 21, 2008 11:00 AM
As Anon said, grow your own greens - don't need a big patch and it is one less area to mow. May I suggest French Sorrell - a citrusy green that stays the same all summer and winters over in AL with a bit or covering. Mix it with your lettuce for much more zing and nutrition.
Posted by: K | March 21, 2008 1:59 PM
It's not just the green leafies. Take a good look at the sacks of "ready to eat" (so-called) "baby carrots": try plating some of the liquid in the bag on EMB and see what happens. (Spoiler: confluent growth with nice green metallic sheen, aka: probable E. coli)
Try contacting local health department to discuss this, and you will be told that the carrots are not a problem because "it is assumed that all vegetables should be washed before being consumed" even as you point out the words "ready to eat" right on the package and further note that parents are sending their kids to school with this "healthy" snack.
Do any of the purchasers of baby carrots wash them prior to eating them? Even if they're washed, they're also pre-peeled, exposing raggedy edges of broken cells, so how can they be cleaned effectively, without resorting to bleach?
I also wonder why HepA shots are so difficult for adults to obtain (from docs following CDC guidelines), given that HepA outbreaks so often come from food handlers.
It's gotten so I prepare nearly all of my own food, carefully, but it sure would be nice to be able to trust a nice restaurant salad now and again.
Posted by: kathleen | March 21, 2008 2:39 PM
Does washing greens really help with contamination? Particularly if they're already chopped into pieces and 'pre-washed' with water containing who knows what?
I recall a kindergarten 'science' project that involved white carnations in a vase with water tinted red with food color. The carnations turned a pretty shade of pink.
I quit with the bagged salads during the spinach contamination, and now grow almost all of my own (organic heirloom) greens. Cheaper too. I've seen organic baby lettuce for as much as $8/lb.
Posted by: ipmat | March 21, 2008 4:34 PM
ipmat: Yes, it matters. For many, if not most, of the foodborne agents it's all about the size of the inoculum. Washing knocks it down a lot. It doesn't make things commercially sterile but it makes a very big difference.
Posted by: revere | March 21, 2008 5:10 PM
Sorry, guess I wasn't clear. I thought the problem was 'little bugs' were getting sucked up INSIDE the spinach, possibly while being watered with contaminated water in the field, and rinsing off the outside didn't help. I don't worry about the big bugs; anything I can see is chicken feed, or would be if I still had chickens!
Speaking of chickens, I *really resent* what's happened to our food supply. Never more than when I make a batch of brownies, go to lick the beater like I did when I was a kid, and remember I can't....because of raw eggs.
Posted by: ipmat | March 21, 2008 5:25 PM
Toles
Posted by: Tim | March 21, 2008 8:13 PM
Tim: LOL.
Posted by: revere | March 21, 2008 8:30 PM
Tim: Cute.
Now I have to wash my salad very careful. I can not die of eating " spinach", who are going to treat my "FDA"?
Posted by: paiwan | March 21, 2008 10:25 PM