Since a few hundred million eggs have been recalled, I'm wondering how salmonella gets into eggs in the first place.
Is it getting on the shells from the environment (or the hen)? Is it inside the egg?
This is mostly a curiosity/science question, so please don't take it as fear mongering, FUD, or any such non-sense. I realize that many eggs are perfectly safe.
Best Answer
There are two basic mechanisms:
To reduce the very common (a few percent) shell contamination, eggs sold commercially have their shells treated (typically washed). After washing only about 50 in every million eggs will still have some shell contamination. The shell contamination may have been there when the chicken laid the egg, from fecal matter, or as a result of plant processing.
In some rare cases the surface salmonella can make it to the inside without breaking the egg: if it was there while the cuticle dried, if the egg is stored at room temperature, or if the environment is moist.