Wow. Check thisarticle:

Now, seemingly more intent at make zero-tolerance a reality, USDA yesterday issued notice that it was mandating an increase in the frequency of its in-plant testing for E. coli O157:H7 in raw ground beef. While this is an improvement, it is but a baby step, since the most frequent testing that will occur under this policy is 4 times per month, and this is only at plants that produce volumes of ground beef greater than 250,000 pounds PER DAY. . . . The one final step that the FSIS needs to take to make this new and much improved approach really work is to eliminate, once and for all, the absurd fiction that a presumptive positive is not a "real" positive test result. Confirmatory testing should be required of all presumptive positive test results.