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Pundit’s Mailbag —
False Positives
Not Surprising

Our discussion of the recent Dole recall, which we covered both here and here, and especially our exasperation on the testing, brought this pointed letter:

We’re not surprised by any of these findings.In fact this is what we would consider the norm.When pulling a second sample from a bag where a PCR presumptive positive has been found and running a second PCR test we will rarely find a second positive.So, not finding a positive in many other bags from the same lot comes as no surprise, and as we’ve discussed earlier for every 8 or 9 PCR presumptive positives we confirm a single finding.

Although it should be noted that the level of confirmations moving from a PCR test for E. coli O157:H7 to the classical confirmation tests are not the same as for Salmonella.

For Salmonella we are confirming less then 12% of our PCR findings.

For E. coli O157:H7 we are working with a much smaller population (fewer positive PCR findings) but our confirmation level is closer to 40%.

What appears to be emerging here is a clear example of why recalls are handled by producers not regulators; a regulator can err on the side of caution without consequences, the producer is impacted regardless of the end result.The looming presence of the regulatory authority has a way of pushing the producer to a more conservative decision.

Following the two high profile fresh produce cases in 2005 and 2006 folks have come to expect that health officials will solve every case as if it were CSI.The 2005 and 2006 outbreaks were atypical. They will become case studies showing how everything is done properly from a regulatory perspective.Future cases will depend more on the statistics generated from the epidemiologist than on the test results of the laboratories, and their conclusions will not be as clear cut.

The fresh produce industry needs to continue emphasizing basic HACCP principles.That means focusing on preventing the introduction of possible physical, chemical and microbiological contaminates.

— Robert F. Stovicek, PhD
Primus Group

So we are brought back to basics. Positives seem to happen without explanation and without being part of a broader contamination. We will probably never know why or trace back a source.

The only solution is old-fashioned vigilance, as Bob tells us: “…focusing on preventing the introduction of possible physical, chemical and microbiological contaminates.”

Many thanks to Bob and to Primus for keeping us on the straight and narrow.

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