On June 4, food regulators began screening beef for six more strains of E. coli beyond the already-monitored E. coli O157:H7. Since that time, 110 samples of beef trim have been tested for non-O157 E. coli; 3 were found to be carrying these bacteria. USDA’s Food Safety and Inspection Service published these initial findings in a results chart this week. The three positive test results represented three different strains of E. coli: O45, O103 and O145, each of which was found once. No samples have yet tested positive for the other three strains: O26, O111 and O121. None of the six samples from imported beef products tested positive for non-O157 E. coli. So far, FSIS is only testing for the “Big Six” E. coli strains in beef trim from slaughterhouses, not in meat that has been processed into a finished ground beef product.The new testing also excludes bench trim and meat from the cow’s head and cheek. In addition to its 110 “routine” tests under the new program, FSIS also conducted 5 “follow-up” analyses. These were likely done on beef that had previously been flagged for potential contamination. One out of these five samples tested positive for a non-O157 strain, yielding a 20 percent contamination rate among the 5 follow-up samples. When these follow-up samples are included in the overall non-O157 count, the number of contaminated samples rises from 3 out of 110 to 4 out of 115, or 3.48 percent of samples. The initial test results don’t hold any surprises, says Dr. Richard Raymond, former Undersecretary for Food Safety at the U.S. Department of Agriculture. Based on previous studies on the prevalence of non-O157 E. coli in meat, he says he would expect anywhere from 2-5 percent of meat to be carrying one of the six strains that FSIS now considers adulterants. One of these studies, commissioned by Food Safety News‘ publisher Bill Marler, found that around 1.9 percent of meat sold in grocery stores carried E. coli strains other than O157:H7. Another study from Texas Tech University got a somewhat higher figure, finding that 4.11 percent of whole meat cuts sold at retail locations were contaminated with a non-O157 shiga toxin-procuding E. coli (STEC). But for right now, this small amount of samples can’t paint the bigger picture, says Raymond. “I think we’ll have to wait a while before we know what percentage of these trim samples are going to test positive,” he says. “When you consider the tens of thousands of tests that have been done for O157s, I would consider this just a drop in the bucket.” FSIS has already tested around 7,000 samples of beef for E. coli O157:H7 this year. This includes all categories of trim as well as finished ground beef product, types that are not currently being tested for non-O157 strains.