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Bugs & Drugs in Pork: Yersinia & Ractopamine

Consumer Reports recently released a study in which they analyzed U.S. retail pork and found trace levels of an adrenaline-like drug called ractopamine in about 20 percent of the samples and a foodborne bacteria that sickens nearly 100,000 Americans every year called Yersina in two-thirds of pork samples.

Ractopamine safety analysis

The National Pork Producers Council tried to address concerns about ractopamine by noting that the levels in meat of this muscle growth promoter, which is fed to pigs in the form of Paylean™ and turkeys in the form of Topmax™, were below the limit set by the UN Codex Commission last summer. What they didn’t mention was that due to outstanding safety concerns, the Commission’s drug residue limit only passed by a single vote out of 143 ballots cast.

The Codex Commission based this drug residue limit in meat on the only human data available, a study of just six people that wasn’t designed to establish safety. At higher doses, the study subjects reported their hearts racing and pounding—so much so that one subject had to be withdrawn from the study. At a lower dose, though, no cardiac changes were noted. So that’s the dose the Codex Commission used to calculate the maximum allowable meat residue and acceptable human daily intake levels.

Just because a certain dose doesn’t cause a problem in six people is no certainty that the dose is safe for everyone. The European Food Safety Authority—Europe’s equivalent to the U.S. Food and Drug Administration—calculated that a study of six people wouldn’t even have the statistical power to pick up a 40 percent change in cardiac output, a key measured endpoint. To detect as statistically significant a clinically relevant change, the study would have required at least 60 people.

Also, the study only looked at the cardiovascular effects of ractopamine. Given its adrenaline-like effects, the drug could also cause metabolic effects in people such as an increase in blood sugar levels or behavioral effects such as restlessness or anxiety.

Finally, all six study subjects were healthy young men. What about particularly vulnerable populations such as children or people with heart disease? The European Food Safety Authority panel concluded that the Codex limit did not sufficiently take these higher risk populations into account. They concluded that the single small human study “can not be taken as a basis to derive an acceptable daily intake…and consequently no proposal for maximum [meat] residue levels could be made.” In other words, we simply don’t have enough data to determine a safe level of drug exposure from meat.

Ractopamine – animal health and welfare

The Council of the European Union recently joined China in reaffirming the ban on ractopamine, citing both human health and animal welfare concerns. Studies over the last decade have shown that pigs on ractopamine may have chronically elevated heart rates, increased stress reactions, and difficulty walking. In fact the warning label reads: ‘‘Caution: Pigs fed PAYLEAN are at an increased risk for exhibiting the downer pig syndrome,” a condition in which pigs are too sick, injured, or exhausted to stand and may be dragged to slaughter.

The pork industry uses an ironic pretext to defend its use of gestation crates – restrictive cages that virtually immobilize breeding pigs for nearly their entire lives. The industry claims this is to keep them from fighting, but at the same time pork producers feed millions of fattening pigs a drug shown to increases aggressiveness and attacks.

Given the human and animal welfare concerns, why does the U.S. pork industry continue to feed this drug to their animals every year?

A meta-analysis was recently published in the Journal of Animal Science. Based on all the studies done to date, pigs fed ractopamine “had an overall carcass cutability advantage of 1.01 percentage units when compared to control pigs.” All this for a 1 percent greater yield.

For more on this drug in the meat supply, see my 6-min. video Ractopamine in Pork.

For more on the drug use by the livestock industry see:

Yersinia – the gift that can keep on giving

The discovery of Yersinia in pork is no surprise. Pigs are considered to be to be the main reservoir for Yersinia enterocolitica and pork products the main source of human infection. While most foodborne pathogens come from a variety of sources, 100 percent of the attributable Yersinia outbreaks reported in the United States from 1999 through 2008 were caused by pork. What was a surprise is the level of contamination of the U.S. pork supply—69 percent of samples tested positive—and the level of antibiotic resistance. Ninety percent of the Yersinia bacteria found contaminating the pork was resistant to one or more antibiotics.

In most cases, Yersinia food poisoning causes an acute “stomach flu” characterized by fever, abdominal pain, and often bloody diarrhea. Severe cases are frequently confused with appendicitis, leading to unnecessary emergency surgery. Long-term complications of infection include chronic inflammation of the eyes, kidneys, heart, and joints. Within a year of a bout of Yersinia food poisoning, victims appear to have a 47-fold higher risk of coming down with autoimmune arthritis. The bacteria may also play a role in triggering an autoimmune thyroid condition known as Graves’ disease.

Yersinia – the role of factory farming

The new findings, published in the January 2013 issue of Consumer Reports, are not surprising given how widespread the infection is in the national herd. The increasing emergence of human infections over the last century has been blamed on the industrialization of the pork industry and higher stocking densities. Inside swine confinement buildings, researchers have been able to culture Yersinia bacteria right out of the air.

The pork industry acknowledges overcrowding pigs is associated with increased health risks, but the trade journal National Hog Farmer cites research showing that when “space was dropped to 6 sq. ft./pig, the building produced 26% more pounds of pork at the same fixed cost.” That entails cramming a 200-pound pig in a space equivalent to about 2 feet by 3 feet. Sometimes, the article concludes, “crowding grow-finish pigs a little tighter will make you more money.”

With so many Americans falling ill from contaminated pork, why are there no industry-wide Yersinia monitoring and control programs in the United States? Perhaps this is because Yersinia enterocolitica doesn’t cause clinical disease in pigs and therefore doesn’t directly affect the industry’s bottom-line. The costs of crowded confinement may instead be passed on to the tens of thousands of Americans who continue to be sickened every year at an annual estimated cost of a quarter billion dollars.

Research from Europe suggests pigs raised using organic methods – which in Europe means more than just what animals are fed – may have 50 times lower odds of harboring Yersinia enterocolitica infection compared to pigs raised on conventional factory farms. After studying a variety of factors, the researchers ended up attributing the low rates of Yersinia infection on organic farms to lower levels of stress among the animals.

If stress is indeed a contributing factor, things may be looking up in Europe. On Jan. 1, 2013 gestation crates for pregnant pigs were banned across all 27 nations of the European Union. Crated sows have been shown to have impaired immunity, thought to be a result of elevated stress hormone levels related to being virtually immobilized for years on end.

Pregnant sows in the U.S., where the majority are still crated, have been shown to have among the highest rates of Yersinia enterocolitica infection. Since infected piglets have been shown to carry the infection through to slaughter, the impact of stress levels on disease resistance of breeding pigs can have human health consequences. Thankfully, major U.S. retailers, restaurant chains, and leaders in the pork industry have started phasing out gestation crates, which may end up benefiting both animal welfare and the safety of the meat supply.

For more on this pork-borne bacteria check out my 7-min. video Yersinia in Pork.

For more videos on fecal matter contamination of the meat supply, see:

The Campylobacter in chicken that I end the Yersinia video on is the Poultry and Paralysis bacteria.

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 – 2015 presentations Uprooting the Leading Causes of Death, More than an Apple a Day, From Table to Able, and Food as Medicine.


Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.

5 responses to “Bugs & Drugs in Pork: Yersinia & Ractopamine

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  1. if you are eating organic and constains statement that no steroids or antibiotics are used can they still contain ractopamine or yersinia?

    1. No ractopamine, but

      “When production types and capacities were compared, the prevalence of Yersinia pseudotuberculosis was HIGHER in organic production than in conventional production”

      Laukkanen, Riikka, et al. “Transmission of Yersinia pseudotuberculosis in the pork production chain from farm to slaughterhouse.” Applied and environmental microbiology 74.17 (2008): 5444-5450.

  2. Are humans more susceptible to pathogens from pigs than from other animals (e.g., cows)? I’m thinking of how heart valves from pigs are used in humans, so we must be generally more biologically compatible.

  3. Some actual facts: Pigs can get human diseases, and yes, some diseases go the other way. I’ve been subscribed to PRO-MED since about 1999, and I’ve yet to see a report of ‘Yersinia enterocolitis’ as far as I can recall, much less one associated with pigs.

    In the Consumer Reports ‘study’, only 128 samples were taken and evaluated–but they also cite that they took ‘148 pork chops and 50 ground pork samples from around the US’. Discrepancies like that give science a bad name! A tiny study like that is as silly as the study cited under the ractopamine portion of the article which used only six people! There is no way that 128 samples is representative of all pork sold in the US, and without links to reputable studies, I can’t give that much credence at all.

    A much better study, of the pigs themselves, is available at and indicated that 3.8% of 2793 swine carried 106 different isolates of this bacteria which *may* be capable of causing human disease. And, of those, all were susceptible to 13 out of 16 antimicrobial drugs tested–which is pretty typical for any bacteria.

    Again, a relatively small sample, perhaps, in comparison to the millions of pigs sent for slaughter each year in the US, but far better done than the one by Consumer Reports!
    Cook your food well, and choose your science with care–you’ll do a better job of protecting yourself that way, and be a lot calmer to boot. :)

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