Transcript: Yersinia in Pork
Every year the federal government tests thousands of retail meat samples for the presence of a four types of antibiotic resistant bacteria, but Yersinia enterocolitica, is not among them. This is despite the fact that nearly 100,000 Americans are sickened by foodborne Yersinia every year. This is yet another public health breach filled yesterday 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 a hundred percent 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, and 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 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 has been associated with increased prevalence among herds. Inside some swine confinement buildings researchers have been able to culture the bacteria straight out of the air.
The pork industry does it because overcrowding pigs may pay, according to the trade publication National Hog Farmer. You can maximize profits by dropping the space per pig to 6 square feet—that’s a 200-pound pig in like 2 feet, by 3 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 doesn’t 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 are 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 estimated cost of 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 lower infection rates 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 1st, 2013, 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 enterocolitica. 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.
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 our 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 slaughter plant. 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.
To put the new Consumer Reports findings in perspective, 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.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring watch the above video. This is just an approximation of the audio contributed by Ashley Rhinehart, RN.
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