When Consumer Reports released the results of a study last week that found most pork was contaminated with Yersinia enterocolitica, the media and bloggers were abuzz with headlines like: “Almost 70 Percent of Pork In Stores Unsafe” (Forbes), “Widespread bacteria and drugs found in US pork samples” (Fox News), and “Consumer Reports analysis of US pork finds majority contaminated” (Los Angeles Times).
Here at Food Safety News, we also reported on the study. The group’s testing of 198 pork samples, 148 of which were pork chops and 50 of which were ground pork, found relatively low levels of contamination for the bugs that regularly make headlines, like Salmonella and Listeria monocytogenes, but a whopping 69 percent of these samples were positive for Yersinia enterocolitica, which can also make people sick.
Reactions to the report were all over the board. As we noted, Congresswoman Louise Slaughter (D-NY) called the results “simply terrifying,” The U.S. Department of Agriculture said the study showed that pork is safe to eat and reminded consumers to cook it properly, and the National Pork Producers Council (NPPC) rebuffed the study as “junk science” that was “designed to scare consumers into purchasing only organic pork.”
It turns out there is a lot of confusion about Yersinia enterocolitica. Because it’s not one of the top pathogens responsible for foodborne illness in the United States, food safety advocates and researchers don’t pay a whole lot of attention to it.
Based on a small number of reported cases, the Centers for Disease Control and Prevention estimate that there are somewhere in the neighborhood of 100,000 cases of yersiniosis (Yersinia infection) in the U.S. each year. According to CDC, the bug can cause fever, abdominal pain and diarrhea, usually lasting one to three weeks.
Health officials know the pathogen makes some Americans sick each year and that pork is a major source of these foodborne illnesses, but there is no government data on how prevalent Yersinia enterocolitica is in the pork supply, nor is there a broad understanding of exactly how prevalent pathogenic (types that can make you sick) of Yersinia enterocolitica are within the species.
The U.S. Department of Agriculture’s Food Safety and Inspection Service has not tested for Yersinia in its baseline assessments, which aim to provide a broad picture of contamination levels across the entire sector.
According to documents posted online, the agency planned to include the pathogen in its 2010-11 baseline study for pork, but ended up not testing for it. A spokesperson for FSIS said Yersinia wasn’t included because the available testing methods “were not reliable for detaching pathogenic serotypes and genotypes of [Yersinia].”
According to the U.S. Food and Drug Administration’s “Bad Bug Book,” Yersinia enterocolitica can be presumptively identified in 36 to 48 hours, but confirmation can take 14 to 21 days. Determining pathogenicity is “more complex,” but the USDA’s Agricultural Research Service and many other labs do have methods for doing so.
One of the biggest criticisms of the Consumer Reports study is that it didn’t break down its findings into pathogenic and non-pathogenic types of Yersinia enterocolitica.
“We tested for all strains of Yersinia enterocolitica — similar to what Food Net (CDC) does to confirm illness from Yersinia,” said Urvashi Rangan, director of safety and sustainability at Consumer Reports. “We say in the story that these are potentially pathogenic and we clearly found a lot of it.”
Food Safety News asked numerous experts and no one knew how to estimate what percentage of Yersinia enterocolitica found on pork is pathogenic — the type that would be a threat to consumers.
“Unless someone types the Y. enterocolitica, it is not possible to put a number on the percentage of pathogenic vs. non-pathogenic organisms,” says Harshavardhan Thippareddi, a food safety professor at the University of Nebraska-Lincoln. “From the study reported in Consumer Reports, they did not type the Y. enterocolitica and hence, it is not possible to determine whether they are pathogenic or not.”
The pork industry responded to the study by asserting that only a few of the many different seroptypes of Yersinia enterocolitica can cause illness, but recent research suggests that a significant proportion of the bacteria found on hog farms may be pathogenic.
A 2007 study published in the Journal of Food Protection found that 10.7 percent of finishing pigs tested positive for Yersinia enterocolitica. Of those isolates, 48.1 percent were found to contain pathogenic genes. A 2005 study conducted by USDA researchers at ARS tested pig feces and found 12.7 were positive for Yersinia, with 43 percent containing pathogenic genes.
Advocacy vs. Research
“My first reaction is that this is Consumer Reports looking for clicks,” said Don Schaffner, a food science professor at Rutgers University, who questioned why the group didn’t share more detail on their study design and methodology. “We’ve known for a long time that Yersinia enterocolitica is a problem in pork, but really the question is: What have we learned from this study that makes a difference for public health?”
While Schaffner said he would prefer to see peer-reviewed research on the topic, he also doesn’t think the pork industry should completely dismiss the results of the study: “It certainly is interesting and it bears further investigation.”
Several researchers noted it can be hard to get funding to study Yersinia and other food safety issues that are lower on the totem pole of public health priorities.
“You certainly want to focus on the things that greatly impact public health,” said Dennis Burson, a professor of meat science at University of Nebraska-Lincoln. “If you’re spending money doing this type of analysis, you want to focus it on the big problems.”
Though Consumer Reports doesn’t discern between pathogenic and non-pathogenic types of Yersinia, the group is quick to point out that the level of antibiotic resistance found is concerning, even if some of the resistance is among non-pathogenic strains.
Several of the isolates found were resistant to one or more antibiotics: 6 of the 8 Salmonella samples, 13 of the 14 Staphylococcus samples and 121 of the 132 Yersinia samples. The study also found MRSA on one sample.
The publication’s policy arm, Consumers Union, firmly believes the widespread use of antibiotics in agriculture is a key contributor to the resistance problem, and the group has been active in pressuring retailers to carry meat and poultry from animals raised without antibiotics.
Pork producers argue that the study, which they say tested too small a sample and wasn’t nationally representative, was presented simply to bolster the group’s advocacy efforts.
“This report was obviously written to support Consumers Union’s claim that antibiotics use in food animal production is the major cause of antibiotic resistance, or treatment failures, in human medicine,” said R. C. Hunt, a pork producers from Wilson, North Carolina and president of NPPC. “The article and Consumers Union disregarded numerous peer-reviewed risk assessments that show any risk to human health from antibiotics use in food animals is negligible.”
The only thing everyone seems to agree on is that consumers can mitigate the risk of contracting Yersinia by carefully handling and properly cooking pork products.
Health officials recommend avoiding raw or undercooked pork, consuming only pasteurized dairy products and washing hands when preparing food after contact with animals and after handling raw meat. Raw chitterlings, or pig intestines, are seen as a particular risk. It’s important to clean hands thoroughly with soap and water before touching infants or their toys, bottles or pacifiers after handling chitterlings.
This story has been updated.© Food Safety News