We are in the midst of another sprouts recall.    Sprouts from Kowalke Organics from Culver City, California are being pulled from shelves over potential contamination with Salmonella.    According to the LA Times:  "Mike Matthews, Kowalke’s owner, told the Associated Press that only one package — with the sell-by date of June 21 — tested positive for salmonella, so far."   There is not yet confirmation of illness associated with this latest recall.  Still, Mr. Matthews comment brings up again how misleading statements like this can be.

A perfect example is last summer’s E. coli O157:H7 outbreak traced to lettuce.  Health officials gathered overwhelming  epidemiological evidence to implicate the product.   The producer, though, kept crowing to the press about how none of the lettuce tested from its plant tested positive.  Of course, health officials were forced to point out that the product tested was CURRENT PRODUCT, i.e. the product in the plant at the time the outbreak was recognized.   Thank goodness there wasn’t STILL contaminated product on hand.  The product actually implicated in the outbreak was long gone, and could not be tested.

In outbreaks involving perishable items, such as produce, finding product produced and packaged at a time that coincides with product implicated in an outbreak is very unusual.  Think about this very plausible, but hypothetical, time line.   Produce goes out, lets say lettuce, processed on July 1.   It hits the shelves on July 5.   On July 7 its purchased, and then consumed two days later on July 9.  The incubation period for E. coli O157:H7 generally runs 2 days to a week.   So let’s say the consumer has onset of symptoms on July 12.  By July 14, the consumer is sick enough to go to the doctor.  If we are lucky, a stool culture is ordered the first day of medical care.  Results return 48 hours later, and now it is July 16.   A good health department is notified of the illness, and interviews the consumer for a food history immediately.  It’s now July 17.  Before health officials are testing product, there usually need to be multiple illnesses that suggest a product as a culprit.  Even assuming the best time line, it is probably nearly three weeks from processing to the opportunity to test product.  By then, product processed on July 1 has been consumed or discarded.

So, the next time you hear a produce supplier tell you that "none of our product has tested positive," bear this in mind.  Such proclamations are essentially worthless at best, and more likely misleading.