Consumers Union study stirs debate on bacteria in pork

Nov 27, 2012 (CIDRAP News) – Consumer Reports magazine has stirred debate about pathogens in pork by reporting a small study in which Yersinia enterocolitica was found in 69% of samples, while more common foodborne pathogens like Salmonella and Listeria were much less prevalent.

Y enterocolitica causes an intestinal illness that manifests as fever, abdominal pain, and often-bloody diarrhea, mainly in children. The illness usually goes away by itself, but it sometimes requires antibiotic treatment, according to the Centers for Disease Control and Prevention (CDC).

The National Pork Producers Council (NPPC) labeled the study "junk science," saying the sample was too small to yield a good estimate of the prevalence of bacteria and only a few strains of Y enterocolitica actually cause illness.

Consumer Reports, published by the nonprofit group Consumers Union, tested 198 raw pork samples, including 148 pork chops and 50 ground pork, from a number of grocery chains.

Besides finding Y enterocolitica in 69% of the samples, the investigators detected Salmonella in 4%, Staphylococcus aureus in 7%, and Listeria monocytogenes in 3%, according to the report. Also, 11% of the samples had Enterococcus species, a potential indicator of fecal contamination.

Contamination was more common in ground pork than in pork chops, the magazine said.

The report also said tests showed that some of the bacteria in the samples were resistant to one or more antibiotics. Specifically, 121 of 132 Y enterocolitica samples, 13 of 14 S aureus isolates, and 6 of 8 Salmonella isolates showed resistance to at least one antibiotic. Methicillin-resistant S aureus (MRSA) was found in one sample.

The investigators tested the organisms for resistance to amoxicillin, penicillin, tetracycline, streptomycin, and other antibiotics, depending on the type of bacteria.

"The frequent use of low-dose antibiotics in pork farming may be accelerating the growth of drug-resistant 'superbugs' that threaten human health," the magazine said.

The CDC says pigs are the most common animal reservoir for pathogenic Y enterocolitica and that infections are most commonly acquired from food, especially raw or undercooked pork. Pork chitterlings (intestines) are especially risky. But the agency agrees with the NPPC that only a few strains of Y enterocolitica are pathogenic.

CDC information on yersiniosis says the agency's FoodNet surveillance system suggests that the number of reported cases per year in the United States is about 1 per 100,000 people, making it much less common than illnesses caused by Salmonella and Campylobacter. For example, in 2011 the number of salmonellosis cases reported to FoodNet was 16.47 per 100,000 people, the CDC said in a July report.

The true number of foodborne disease cases is typically much higher than the reported number, however, since many people don't seek treatment.

In an e-mailed statement, the NPPC charged that the Consumer Reports study was "designed to scare consumers into purchasing only organic pork by using junk science against pork from conventionally raised hogs."

"The low number of samples tested (198) does not provide a nationally informative estimate of the true prevalence of the cited bacteria on meat," the council said.

It added that Y enterocolitica comes in more than 50 serotypes, only a few of which are pathogenic. The magazine either didn't conduct, or didn't report the results of, tests to show whether the strains it found were pathogenic, the statement said.

Further, federal surveillance data show that yersiniosis cases have declined more than 50% since 1996, the council said. It added that cases are so few that the US Department of Agriculture doesn't test pork for Yersinia.

The council also asserted that the antibiotics the study focused on in the resistance testing "are in classes that are not considered critically important to human health" and that almost every bacterial species is resistant to some antibiotics.

The NPPC charged that the study was designed to support Consumers Union's claim that antibiotic use in food animals is the major cause of antibiotic resistance in human diseases, a claim the NPPC rejects.

The US Food and Drug Administration is currently trying to reduce the use of antibiotics in food animals, with the aim of preserving their usefulness in human medicine. In April the agency announced a voluntary strategy designed to move animal-drug producers, veterinarians, and farmers away from using antibiotics for promoting growth in farm animals.

The Consumer Reports article includes safety tips for pork preparation and handling. It advises that whole pork should be cooked to 145ºF and ground pork to 160ºF.

See also:

Nov 27 Consumer Reports article

CDC information on yersiniosis and Y enterocolitica

Jul 30 CIDRAP News story "2011 brought little change in foodborne disease incidence"

Apr 11 CIDRAP News story "FDA spells out voluntary plan for cutting ag antibiotic use"

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