The FDA is investigating a nationwide outbreak of Salmonella in  shell eggs.

While many believe that contaminated water and feed and rodents are to blame, if you go further back into the causation you will find that the egg is contaminated because of the absence of salmonella pullorum in the gut of the chicken.

Programs to combat the one disease of chickens in the 1980’s some believe led inadvertently to the colonization of the gastrointestinal tract and reproductive organs of chicks by the human pathogen, SE. It doesn’t necessarily mean that the first event caused the other, but there is biological plausibility to this argument and the temporal association I think is striking. Especially, given this disease occurred in several parts of the world almost simultaneously. So the rodent that has been in the hen house for millennia causing limited human disease (through contaminated egg shells) becomes now a vector for a widespread invasive disease of poultry and humans and spreads to other food animals. Not to minimize the rodent’s infectious properties and need for control, but human meddling with bacteria doesn’t always turn out for the best for mankind. Interestingly, Salmonella pullorum is not treated with antibiotics, culling the bird is the intervention. 
Denmark has been successful in control of SE in broiler chickens, layer hens, and pigs through careful surveillance, culling, farm sanitation, pasteurization, and sanitary slaughter.
Denmark has now has the safest eggs in the world. And they achieved this only by an effective industry-government partnership, something we should take special note of, given the positive political climate in the US right now. See the paper from CDC below for a review of the Danish approach.