Factory-farmed pork is hardly an ideal food—but pigs from small farms might be more likely to make you sick


In previous Atlantic posts I've worked hard to explain the underlying reasons for my disdain of animal agriculture. Those who've engaged my arguments will know my position well enough: I fundamentally oppose raising animals for food that humans don't need. This claim holds true regardless of how the meat is produced or consumed.

I mention this point because the study I'm about to highlight could easily be distorted. The report, published in the February 2011 issue of Foodborne Pathogens and Disease, challenges the perception that intensive animal farming is more likely to spread foodborne pathogens than free-range systems. My choice in drawing attention to this counterintuitive article is decidedly not to argue that factory farms are okay and that we should all go out and support Tyson's. To the contrary, I want to advance the more radical notion that animal farming in general—whether confined or free-range—is fraught with unique problems that we could easily avoid by not eating meat.

Two other caveats before I summarize the article. First, although this study took place without corporate funding, the author—Dr. Peter Davies—has accepted support from the pork industry in the past. Whether or not past support skews future research remains an open question, but it's important to note that the study was published in a peer-reviewed, world-class journal and is based on scores of other studies that found similar results. And second, I'm well aware that the main concern that jumps to mind when it comes to factory farming is often how low-grade antibiotics use leads to potentially deadly, antibiotic-resistant pathogens. This is undoubtedly a huge problem. But this study addresses only foodborne diseases, and thus so does my analysis. This focus is not meant to dismiss or downplay the pressing problem of antibiotic resistance.

The study in question is an exhaustive analysis of existing evidence on the connection between intensively managed pig farming and foodborne parasites. The article caught my eye because Davies, of the University of Minnesota, attempts something uncharacteristic for an article published in a professional scientific journal. He begins by chiding the mainstream media for its selective reporting on this controversial topic. And not very gently.

"Misinformation in public discourse," Davies writes, "has achieved pandemic potential with the rise of blogging and other social networking tools." Discussions of food and agriculture, he continues "are mostly ideological and heavily value laden." Scientists, he argues, must do more than practice sound science. They must exhort the "scientific community . . . to be more visibly engaged in refuting misinformation as well as presenting new information." What's needed is something sorely lacking in so much popular writing about animal agriculture. In essence, "factual accountability."

Lecture delivered, Davies drops his bomb: "Available evidence does not support the hypothesis that intensive pork production has increased risk for the major bacterial foodborne pathogens." Nor does it support the opinion "that pigs produced in alternative systems are at reduced risk of colonization with these organisms." In fact, Davies explains, "pigs raised in outdoor systems inherently confront higher risks of exposure to foodborne parasites."

These claims will surely strike food purists as heresy. But Davies's evidence is compelling. Take Trichinella spiralis. This is a nematode parasite that killed thousands of consumers a year in the late 19th century but is extremely rare today. Davies attributes this impressive multi-decade reduction to the improved management practices of modern swine production. Rodent control and regulated feeding practices, he explains, have "practically eliminated the risk of infection." If a comparison to the 19th century seems disingenuous, note that the 138 cases recorded by the Center for Disease Control between 1997 and 2006 represent a 95 percent decrease in annual infections since the 1940s, and a 76 percent decrease since the 1980s.

During this 10-year span (1997-2006), there were only 15 recorded cases of T. spiralis, nine of which came from commercial pork operations. The other six were linked to "home-raised or direct-from-farm swine." Given that commercial swine facilities produce 100 times more pigs than free-range systems, these numbers suggest that, on a pig-by-pig basis, there's "an 80-fold greater risk (per pig produced) of trichina infections resulting from eating niche market versus commercial pork products." I suppose there are a million ways to quibble with these numbers, but they nonetheless seem consistent with Davies's larger claim that "it is inevitable that pigs with outdoor access will be at greater risk of Trichinella infection due to exposure to wildlife reservoirs."

A far more common parasite that Davies addresses is Toxoplasma gondii. It's likely that a third of us have been laid low by this nasty protozoan, one that accounts for about 75 percent of all foodborne illnesses in the United States. Pork presents the greatest risk of exposure among commercial meats. A 1983-84 national assessment "found that 23% of market hogs and 42% of sows were seropositive for Toxoplasma." As for the actual presence of Toxoplasma in pork, a 1960s study found a 32 percent rate of infection in pork loins. These are bad numbers by any measure.

Such alarmingly high figures sparked regulators and producers to heighten sanitary measures. By the 1990s, matters had improved considerably. A 1995 study done on confined hogs in North Carolina found one pig among 1,752 that was seropositive for Toxoplasma. More recently a 2008 study of 74,000 market hogs in the United States found a .8 percent seropositive rate. Rates declined, moreover, as farm size increased. The highest rate of prevalence—2.6 percent—occurred on farms producing less than 1,000 pigs per year. Interpreting this data, Davies once again concludes that "the inevitability that pigs with outdoor access will be at elevated risk of Toxoplasma infection is consistently reflected in studies from various countries."

The story continues with Salmonella. Finding reliable figures on Salmonella prevalence before the onset of large-scale confinement is hard. But, using "convenience sampling," Davies estimates that Salmonella rates may have been between 27 percent to 78 percent. Today, studies have found rates closer to 7 to 10 percent. And while the correlation between herd size and Salmonella rates is by no means consistent, the most recent examination (2010) of seroprevalence and herd size found that "the odds of being a high seroprevalence herd were three to six times higher for farms with less than 1000 pigs inventory than larger herds."

Finally, there's "the most lamentable and preventable public health problem" linked to pork consumption globally, T. solium. Because this parasite thrives where "sanitation is poor and traditional, free-range scavenging pig production is practiced," it's not a huge problem in the United States (there were only 221 deaths from T. solium between 1990 and 2002 in the U.S.). But it's pervasive and deadly throughout the developing world. Davies's reason for analyzing T. solium is, yet again, to show how "methods of modern confinement swine production virtually eliminate any risks of porkborne transmission of T. solium." What "endemic countries" must do in order to eliminate the parasite, he claims, is undertake "the simple corralling of pigs."

Davies's publication primarily leaves me with two related reactions. The first is why has this study not been in the news? I'm not suggesting that it's the final word on anything. But should it not be part of a larger discussion we're having about meat production? No matter how one feels about the findings, they strike me as central to food safety concerns. Can you imagine how the food media would have lit up if a study had found the opposite set of conclusions? (In fact, I waited two months after Davies's study was published to see if it got any media play before I chose to natter on about it here. Virtually nothing has appeared.)

Davies is equally miffed by the silence, explaining in an email to me that "the absolute absence (as far as I am aware) of any commentary from any groups tending to be critical of modern agriculture is more than a little surprising." His "hunch" is that his paper has zero "memetic potential in the blogosphere" and, as a result, "does not reinforce the narrative of critics of modern food production and hence has been blissfully ignored." In my experience interviewing people in agribusiness, I can say with confidence that many, many large-scale farmers feel that their side of the story is never told in the mainstream media.

My second and final reaction is that the study hasn't seen the light of day because it directly challenges one of the more sacred assumptions of free-range meat. Nobody, especially food writers who make their sympathies public, likes to dice up their own deeply held beliefs. I'm fully aware that there are many other problems with confined production besides zoonotic disease (such as pure cruelty, pollution, and, as noted, the rise of antibiotic-resistant pathogens), but evidence suggesting that one's chances of getting sick from free-range pork are the same or even higher than with factory-farmed options is fairly damning news for those who advocate smaller, alternative ways of getting pork to the plate.

As I have written here before: "Every study has a counter-study." I hope readers can debunk Davies's conclusions. But until they do I'm holding firm to my own sacred assumption that the best way to avoid getting caught in the scientific crossfire between the free-range and confinement options is to simply remove oneself from the battlefield.

Image: The Pug Father/flickr