Levels of contamination in the U.S. is about 50 pounds per year, based on 2009 Department of Agriculture data.

We tested 148 samples of meat from pork chops and 50 from ground pork, and found that almost 70 percent tested positive for yersinia enterocolitica, which can infect people who eat raw or undercooked pork.

Enterococcus, staphylococcus aureus, salmonella, and listeria monocytogenes were less common in the samples we tested. Twenty-three percent of the samples harbored none of the tested bacteria.

The pork samples we analyzed came from many brands, but we lacked enough samples within each brand to say whether one was more or less contaminated than another.

Big brands we tested: Denmark, Farmer John, Farmer John California Natural, Farmland, Hempler’s, Hormel, Hormel Natural Choice, Nature’s Promise, Nature’s Rancher, Northwest Finest, Roseland, Smithfield, Swift Premium, and Tender Choice.

Store brands we tested: Angelo Caputo’s, Bashas’, Bristol Farms, Butera, Dominick’s, Edmar, El Toreo Market, Food 4 Less, Fred Meyer, Fresh & Easy, The Fresh Market, Giant, Meijer, PCC Natural Markets, Publix, Ralphs, Safeway, Save-a-Lot, Sprouts Farmers Market and Farmers Market Old Tyme, Ultra Foods, Viet Wah, Vons, Walmart, Wegmans, Weis, Whole Foods, and Winn Dixie.