Transcript: Yersinia in Pork
Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.
Every year, the federal government tests thousands of retail meat samples for the presence of four types of antibiotic-resistant bacteria. But, Yersinia enterocolitica is not among them. This, despite the fact that nearly 100,000 Americans are sickened by foodborne Yersinia every year. This is yet another public health breach, filled this week by Consumers Union.
Pigs are assumed to be the main reservoir for the pathogen, and pork and pork products, the main source of human infection. Most foodborne pathogens tend to come from a variety of sources, but 100% of the attributable Yersinia outbreaks reported in the United States over the last decade or so were caused by pork.
So, 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; often bloody diarrhea. Sometimes cases can be confused with appendicitis, leading to unnecessary emergency surgery. Long-term consequences of infection include chronic inflammation of the eyes, kidneys, heart, and joints. Within a year of a bout of Yersinia food poisoning, victims are at 47 times the risk of coming down with autoimmune arthritis. And, the bacteria may also play a role in triggering an autoimmune thyroid condition, known as Graves’ disease.
How widespread is Yersinia in U.S. pigs? A national USDA survey of fecal samples found half of American herds tested were infected. The emergence of human infection over the last century may in part be due to changes in the meat industry, such as slaughter plant consolidation, and an increase in farm size and intensification of production. Higher stocking densities of pigs on factory farms is one of the factors that’s been associated with increased prevalence among herds. Inside some swine confinement buildings, researchers have been able to culture the bacteria right out of the air.
The pork industry crowds pigs because overcrowding pigs may pay, according to the trade publication National Hog Farmer. You can, evidently, maximize profits by dropping the space per pig to six square feet—that’s like a 200-pound pig in the equivalent of two feet by three feet. They acknowledge this presents some problems—inadequate ventilation, increased health risks—but, sometimes, “crowding…pigs a little tighter will make you more money.”
The equation for pork producers is even simpler when it comes to Yersinia, since the bacteria does not cause clinical disease in pigs. Thus, it does not present a production problem. The fact that the industry bottom line isn’t directly affected, no matter how high infection rates climb, may explain why there’s no industry-wide Yersinia monitoring and control programs in place in the United States. The costs of crowded confinement can simply be passed on to the tens of thousands of Americans who continue to be sickened every year, at an annual cost estimated at a quarter billion dollars.
Research from Europe suggests pigs raised using organic methods may have 50 times lower odds of harboring infection, compared to pigs raised conventionally. Unfortunately, you can’t really extrapolate that to the U.S., since organic production here is really more about what animals are fed, rather than how they are treated. The researchers attribute the lowered infection rates to factors like lower stocking densities, and lower levels of stress among the animals.
If stress is indeed a contributing factor, things may be looking up in Europe. On January 1, 2013, just about a month away, gestation crates for pregnant pigs are going to be banned across all 27 nations of the European Union—whereas 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 infection. Though consumers don’t directly eat as many of the moms, the sows can be a source of infection for piglets, who can then carry the infection through to slaughter.
“Practices that restrict natural motion, such as [these] sow gestation crates, induce high levels of stress in the animals and threaten their health, which in turn may threaten [our] health [too].”
Crated sows have been shown to have impaired immunity—thought to be as a result of elevated stress hormone levels, related to the frustration of normal maternal behaviors, like nest building.
Yersinia 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 break the Yersinia cycle from farm to fork is to pay producers an incentive bonus if they keep Yersinia-free flocks. That’s the carrot. And the stick is that fresh meat would 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 logistic problem,” it could be actually 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 slaughter plant. “By sealing off the [excised] rectum with a plastic bag” during evisceration, you may get a ten-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 pig slaughterhouses in Norway.
Let me end by putting the new Consumer Reports finding in perspective. Yersinia in pork ranks only sixteenth in terms of the greatest foodborne disease burdens 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 retail meat survey released this year.
Then comes the Toxoplasma brain parasite in pork; Listeria in deli meat; and Salmonella in, again, poultry.
So, as concerning as this new report may be, the greatest safety concern may be the original white meat.
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