The ultimate safe food is obviously that you raise/grow yourself under healthy conditions. I don't have any worry at all about my eggs, laid by my chickens. They run the pasture all day and are no more likely to become diseased than a kid playing in the dirt. (The lack of which - playing in the dirt - is likely responsible for the fact that every third kid is miserably allergic to something, a situation unheard of my youth, before children were condemned by their ridiculous parents to being raised entirely indoors.) And my immune system is in nice shape and can handle routine exposures.
But as to the outside of commercial eggs, whatever the chickens are voiding will cross-contaminate, but commercially produced eggs in the U.S. are washed in detergent and 120F water. (Although in Ireland, Grade A eggs, the only kind that can be sold retail, are NOT to be washed.) Given conditions in our commercial egg plants, it's probably good they're washed, although I suspect it's more an appearance issue. (Free range and pasture eggs get visibly dirtier than commercial eggs, but it's a "clean" dirt.)
Besides, dirt is good for you. Mycobacterium vaccae, a soil microbe, is now thought to improve you mood by targeting the same serotonin producing centers addressed by Prozac. They also help correct allergies by strengthening the immune system. Get dirty - Be happy.