The American Council for Science and Health published a brief report on the current massive commercial egg recall in the U.S. Read it for the CDC’s tips on avoiding Salmonella infection.
I had thought the Salmonella germs were simply on the surface of the eggs. Not so, according to ACSH: the hens’ ovaries are contaminated, so the germ ends up in the egg white, yolk, and shell.
Diabetic Mediterranean Diet 
How does that even happen???
This is why it is best to buy eggs from small local growers Nell
Apparently the bacteria can live in the hen’s ovary without causing sickness in the bird, at least not right away. [Ever?]
In thinking about a human counterpart, all I can come up with offhand are 1) Mycobacterium tuberculosis that can set shop in a lung, then later (or never) spread and cause disease, and 2) herpes zoster virus we acquire during chicken pox, then it hibernates in a spinal nerve for 60 years then sprouts as shingles.