Ractopamine and Yersinia in U.S. Pork

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Earlier this year, China rejected 200,000 pounds of pork from the United States after discovering residues in the meat of an adrenaline-like drug called ractopamine, which is fed to U.S. pigs (Paylean™) and turkeys (Topmax™) as a growth promoter to improve muscle yields. What about the domestic U.S. meat supply? Last year’s report from the USDA National Residue program claimed 310 pigs were tested (out of about 10 million slaughtered). The 2012 report listed the number of tested pigs at zero. That’s why it’s so important to have public interest organizations such as Consumers Union, publisher of Consumer Reports, to fill the gaps.

This week Consumers Union released a report in which they analyzed 240 U.S. pork products and found trace levels of ractopamine in about 20% of retail pork sampled. In response, the National Pork Producers Council tried to allay concerns by noting that the levels found in U.S. pork chops were below the ractopamine residue limit set by the UN Codex Commission this summer. What they didn’t mention was that out of 143 ballots cast, the Commission came within a single vote of setting any safe levels in pork given “outstanding safety concerns” raised by Europe. The National Pork Producers Council also failed to mention the residue limit was based on a single human study that only had six people in it.

That six person study was exhibit #1 in the European Food Safety Authority’s analysis of the questionable safety of the drug. EFSA is Europe’s equivalent to the U.S. Food and Drug Administration. The experiment in question was a preliminary study designed not to establish a safety level, but to find a suitable test dose for a larger study that never happened. (Ractopamine was originally developed as an asthma medication but it didn’t appear to work).

The study involved giving these six men between 5 to 40mg of ractopamine. At the higher levels, the subjects reported their hearts racing and pounding—in fact one of the six subjects was withdrawn from the study because he apparently couldn’t take it. At 5mg, though, no cardiac changes were noted. So that’s the dose the UN Codex Commission used to calculate the maximum allowable meat residue and acceptable human daily intake levels. Just because that dose didn’t cause a problem in six people, though, doesn’t necessarily mean that level is safe. The EFSA panel calculated that a study of 6 people wouldn’t even have the statistical power to pick up a 40% change in cardiac output, a key measured endpoint. To detect as statistically significant a 10% change in blood pumping the study would have required at least about 60 people.

In addition, the study only looked at the cardiovascular effects of ractopamine. Given the adrenaline-like effects could expect metabolic effects such as an increase in blood sugar levels, muscle tremors, or behavioral effects such as restlessness, apprehension, or anxiety.

Also, all six study subjects were healthy young men. What about particularly vulnerable populations such as children, those with heart disease, or those on certain medications? The panel concluded that the UN limits did not sufficiently take these higher risk populations into account.

The European Food Safety Authority 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 human data to determine what the safe level in meat may be.

Last month the Council of the European Union joined China in reaffirming the ban on ractopamine, “[s]tressing that the policy…is based on persisting scientific uncertainty about the safety of products derived from animals treated with this substance…and also takes into account concerns on animal health and animal welfare….” 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 in chains.

It’s ironic that pork industry continues to defend the use of gestation crates for pregnant pigs on the pretext of preventing aggression between the sows. Mother pigs are confined for nearly their entire lives in crates so restrictive they can’t even turn around. The industry claims this is to keep them from fighting while at the same time feeding millions of growing 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 millions of pigs every year? This month a meta-analysis was 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” (74.70% vs. 73.69%). All this for a 1% greater yield.

Watch my video Ractopamine in Pork for more.

Another public health breach filled this week by Consumers Union was testing for Yersinia enterocolitica in pork. Every year the U.S. Centers for Disease Control and Prevention tests thousands of retail meat samples for the presence of a few types of antibiotic resistant bacteria, but Yersinia is not among them despite the fact that nearly 100,000 Americans are sickened by foodborne Yersinia every year.

Pigs are considered to be the main reservoir for Yersinia enterocolitica and pork products the main source of human infection. While most foodborne pathogens tend to come from a variety of sources, 100% of the attributable Yersinia outbreaks reported in the United States from 1999 through 2008 were caused by pork.

How contaminated is the U.S. pork supply? Consumers Union tested nearly 200 pork samples from cities across the country and found more than two thirds contaminated with Yersinia, 90% of which were resistant to one or more antibiotics.

In most cases Yersinia food poisoning just causes acute gastroenteritis characterized by fever, abdominal pain, and often bloody diarrhea. Severe cases are frequently confused with appendicitis, leading to unnecessary emergency surgery. Long-term sequelae of infection include chronic inflammation of the eyes, kidneys, heart, and joints. Within a year of a bout of Yersinia food poisoning, victims may be at 47 times the 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 enterocolitica is widespread in U.S. pigs. A national USDA survey of fecal samples found about half of American herds are now infected with strains pathogenic to humans. The increasing emergence of human infection over last century has been blamed on the industrialization of the pork industry. Higher stocking densities of pigs on factory farms is one of the factors that has been specifically associated with increased Yersinia enterocolitica prevalence in herds. Inside some swine confinement buildings researchers have been able to culture the bacteria straight out of the air, as well as from inside the nostrils of CAFO workers.

The pork industry acknowledges overcrowding pigs is associated with increased health risks, but the trade journal National Hog Farmer reports 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’s cramming a 200 pound pig into the equivalent of about a 2 by 3 foot space. Sometimes, the article concludes, “crowding grow-finish pigs a little tighter will make you more money.”

The equation for industrial pork producers is even simpler when it comes to Yersinia enterocolitica since the bacteria doesn’t cause clinical disease in pigs. The fact that the industry bottomline isn’t directly affected no matter how high infection rates climb may explain why there are no industry-wide Yersinia monitoring and control programs in place in the United States. Such costs can 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 may 50 times lower odds of harboring Yersinia enterocolitica infection compared to pigs raised conventionally. It is unlikely these results can be extrapolated to the United States, though, since organic production in the U.S. focuses more on what animals are fed rather than how they are treated. For example in Europe, organic pigs are allowed outside. 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 January 1st, 2013, gestation crates for pregnant pigs are going to be banned across all 27 nations of the European Union. In the U.S. where crating continues to be a predominant practice, pregnant sows have been shown to have among the highest prevalence of Yersinia enterocolitica. Though consumers don’t directly eat as many of the moms, the sows can be a source of infection for piglets who can carry the infection through slaughter.

Crated sows have been shown to have impaired immunity, thought to be a result of elevated stress hormone levels related to the frustration of normal maternal behaviors like nest building. Yersinia enterocolitica is one of the reasons why the disease resistance of mother pigs matters when it comes to public health. Thankfully, major retailers, restaurant chains, and leaders in the pork industry have started phasing out gestation crates, which may end up improving the welfare of both animals and humans.

Another proposal to help break the Yersinia cycle from farm to fork is to pay producers a premium for animals maintained in Yersinia-free herds. Since 1996 some in the agriculture policy arena have even proposed that fresh meat should only be allowed from infection-free herds, diverting pork from infected herds to just making pre-cooked products. “Although such a two-way splitting of pig-meat production would pose a logistical problem,” researchers acknowledge, “it should actually be possible…[if] enough emphasis were to be placed on cost/benefit for public health.”

There are also measures effective at reducing Yersinia contamination of the meat in the slaughterplant. Studies from Europe have shown that “bagging the rectum” by sealing off the excised rectum with a plastic bag during evisceration may result in a 10-fold drop in carcass contamination. According to data from the Norwegian National Institute of Public Health, human Yersinia infection rates dropped about 25% after the introduction of the plastic bag technique across about 90% of the pig slaughterhouses in Norway.

Earlier this year, the National Pork Board officially changed their quarter-century old slogan from Pork: The Other White Meat,” to “Pork: Be Inspired.” Given the new Consumer Reports findings, maybe it should it be changed to “Pork: Be Expired.”

To put the new data in perspective, though, Yersinia in pork ranks 16th in terms of greatest foodborne disease burden in the United States. The worst in terms of societal cost and quality-adjusted years of life lost is poultry-borne Campylobacter bacteria, found contaminating 38% of chicken breasts in the latest CDC retail meat survey released this year. Then comes the Toxoplasma brain parasite in pork, Listeria in deli meats, and Salmonella in, again, poultry. So as concerning as this new report may be, we are probably still more likely to get sick eating the original white meat.

Watch my video Yersinia in Pork for more.

-Michael Greger, M.D.

Image thanks to Flickr / sean dreilinger

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