Reflections on a Bad Egg

In regards to the current recall of a bazillion eggs, can anyone explain to me how the salmonella gets INSIDE them?  We lived in Moscow during the bird flu epidemic, and all we had to do was wash our eggs off before cracking them in order to prevent the bacteria on the shell from entering the insides. With the current recall, it seems that the bacteria is in-born (or in-unborn, poor little yolks). How does it work its way through the hen's system and end up inside the egg? At least, that's what I'm assuming is the problem, or else wouldn't "they" simply advise us to scrub our eggs before cooking and eating?
I heard on NPR not serve eggs with runny whites, but, in fact, they are recalling all those eggs.  Taken together, it seems to me to mean that the eggs are already bad on the inside.  Also, you have to deny yourself raw Toll House Cookie dough. That's terrible!

And what are the implications for humans? Plenty of women eat junk food and smoke and, I dunno, eat dirt until they get pregnant. They may show exemplary behavior once they know they're about to blow up like a blue whale, but not beforehand. This doesn't seem to affect human embryos. Oh, wait, maybe it explains a lot about the human race. No, no, I don't think so.
The eggs seem to be pre-infected.  Can anyone explain it to me?