When I first moved to Iowa in 1998, many people asked if I was related to a person named “Hurd” or a person they knew up north. I was disappointed to say no, as my family is from the Southeast. Even though we had the same name, we were not related. The same fact needs to be considered in the current Salmonella heildelberg outbreak. Because many people are infected with serovars (like a species, or more like a breed) by the same name does not mean the cases are related. Actually, there are many many strains (subtypes of the serovars) of Salmonella heildberg. Differing strains can mean that they are only distantly related or not related at all. In fact, CDC has reported at least seven different strains in this outbreak.
What this means is the Salmonella which is sadly making folks ill could come from many sources. Not all those sources need to be poultry. Therefore USDA does not find a “smoking gun” at Foster Farms. However, they have found some “smoke”- they have evidence that Foster has been having some ongoing challenges with their Salmonella control. So USDA has cracked down on what is happening but has not implemented a recall.
To implement a recall, USDA must find specific evidence that a certain production period is liable for the illness, then they can implement a recall. As Dr. Englejohn mentioned, they have not found that evidence. Note that recalls are not highly effective at protecting public health, – cooking is.