I’m not sure the source is from not roasting the peanuts properly. It might be in the processing plant itself - in the equipment or somewhere along the line it’s gotten into another ingredient.
In the cantaloupes that were infected with listeria, it turned out it didn’t come from the melons in the fields, but the packing plant. So, all the melons that the farm left in the fields to rot thinking they may be infected, were okay.
Well, FWIW, my money’s in contaminated peanuts that weren’t roasted hot and/or long enough to kill the salmonella.