White Coat Underground

Salmonella–a little background

You’ve probably read about the current Salmonella outbreak. It’s a fine example of what can happen when food is produced and distributed on an industrial scale—even one small contamination event can spread widely in the food supply, and there isn’t much of a system in place to follow the trail of contaminants. Others have covered the public health implications of this outbreak, so I’d like to examine some other facts that make this outbreak disturbing.

Salmonella likes non-human animals

Some species of Salmonella cause typhoid fever. Typhoid fever, a nasty epidemic disease of humans, is easily spread, but easily controlled. Humans are the only significant reservoir for the species of Salmonella that cause typhoid fever, so once you control humans and their water and waste, you can control and prevent outbreaks. The species that cause gastroenteritis (or “stomach flu”) are not so picky about hosts. They can infect many different animals, so even if you can control humans and their waste, you still haven’t controlled a large reservoir of potential trouble. Eggs are commonly contaminated with Salmonella, and outbreaks do to other foods are common. Meticulous food preparation can often prevent infection—thorough cooking of eggs, proper handling of meats. But the current outbreak is a bit more tricky.

Salmonella is easily killed with cooking

That’s great, if it contaminates food that you cook. In this case, peanut butter for industrial-scale use was contaminated. In all probability the peanuts for the product are from many different places, and many batches of butter may have been combined. But even more troubling is that peanut butter is not a product that people normally wash or cook. You simply open it and eat it. Lucky for Salmonella, unlucky for you. When meat or eggs are contaminated at the source of production, we still have a fighting chance through cooking. If it’s peanut butter, all is lost.

You don’t have to be sick to spread it

Not unique to this outbreak is the fact that a person can carry Salmonella and excrete it in their stool without becoming ill. Not only that, but compared to the dose necessary to become ill, it doesn’t take as many organisms ingested to turn someone into a carrier.

Natural defenses—some gaps

The treatment of gastro-esophageal reflux disease has been revolutionized by the introduction of H2-blockers such as famotidine (“Pepcid”) and PPIs such as omeprazole (“Prilosec”). These medications are very effective, and very safe. But (and you knew there had to be a “but”), these medicine work by raising gastric pH, which weakens one of our defenses against Salmonella. The bacterium doesn’t like dropping into a cauldron of acid, but it’s just fine at the relatively higher pH of a stomach treated with omeprazole. This stuff is over the counter, so millions of people take it, rendering them more susceptible to infection, should they be unlucky enough to encounter contaminated food.

Antibiotics—stop asking for them, please

Antibiotics can reduce the normal flora of the GI tract. Some studies have shown that the disruption of normal intestinal flora with antibiotics renders people more susceptible to infection.

What do I do now?

The usual precautions are always a good bet, among them:

  • Wash fruits and veggies thoroughly
  • Salmonella often contaminates the surface of meat (via intestinal contents/poo), so make sure any surface that touches the meat’s surface is thoroughly decontaminated. Also, ground meats are basically “all surface” so they must be cooked well.
  • If the CDC or FDA or other agency recommends avoiding a particular food, take them seriously.

Many cases of food-borne illness can be prevented at the consumer level—the current outbreak makes that a bit harder. Eat carefully.

Comments

  1. #1 Strider
    January 20, 2009

    Hey, not a comment on the post but about your podcast. I really enjoy it for one. When I downloaded ‘cast #5 I got nothin’. Is there something wrong with the site or what?

  2. #2 MKandefer
    January 20, 2009

    How can this be? Isn’t the FDA and CDC in bed with Big Peanut Butter and not looking out for our health? It must be because one can buy natural peanut butter from manufactures looking out for our health, and not our wallets.

  3. #3 PalMD
    January 20, 2009

    Hmm…thanks for letting me know, strider. I thought i’d finished debugging it yesterday evening.

  4. #4 khan
    January 20, 2009

    Meticulous food preparation can often prevent infection—thorough cooking of eggs, proper handling of meats.

    I’m not supposed to eat raw meat?

    But (and you knew there had to be a “but”), these medicine work by raising gastric pH, which weakens one of our defenses against Salmonella. The bacterium doesn’t like dropping into a cauldron of acid, but it’s just fine at the relatively higher pH of a stomach treated with omeprazole.

    I thought so.

  5. #5 W T Frak
    January 20, 2009

    Luckily, it was not every brand of peanut butter, and not the popular name brands.

    Unluckily, it was a kind often provided to poorer people, who are also less likely to see the news, and hear about the danger, and know what to do about it, and be able to afford discarding jars of food.

    That said, it seems Elvis was on the right track, having his peanut-butter-and-banana sandwiches toasted.

  6. #6 ERV
    January 20, 2009

    Neat side-fact that cant help people at home avoid getting sick: Salmonella enterica is icky because of genes it stole from phages, like nasty effectors for Type III secretion systems.
    :P

    Bacteriology got a lot easier for me when I just started connecting it all to virology and evilution.

  7. #7 Rogue Epidemiologist
    January 21, 2009

    People are quick to shrug off the King Nut name because it’s not a common brand of jar peanut butter. Problem is, King Nut and other wholesale PBs are repackaged with new names, usually generics, or they’re used in other products, hence all the PB cracker recalls. I wouldn’t be surprised if it was being used in candy bars, too, though I figure Reese’s makes their own (*gulp* I hope).

    We’ve been following the Salmonella enterica Typhimurium thing for well over 4 months now. Given that Peter Pan PB was implicated last year (or was it the year before?), PB was already on our list of considerations.

    I don’t eat much PB. It’s too calorie dense.

  8. #8 The Perky Skeptic
    January 26, 2009

    Umm… this is a dumb kinda question. When I make icing with a recipe that requires a couple of raw egg whites, am I reducing the risk of Salmonella contamination by washing the eggs with soap and water before I crack open the shell, or am I merely performing an obsessive-compulsive ritual over my food? :)

  9. #9 PalMD
    January 26, 2009

    Prob the latter

  10. #10 The Perky Skeptic
    January 27, 2009

    Another obsessive-compulsive ritual bites the dust!