The claim is that individual laying hens carry the bacteria and can infect an egg they are assembling. Even with an infected chicken only one egg every once in a while is found infected.

Flocks identified with this trait are being culled in the U.S., and I understand in England. Whether there is actually a health hazard with properly stored and handled eggs is subject to debate. Humans are the major carier of this bacteria.

Meanwhile, raw eggs and "undercooked" eggs (the only way to make a proper omelet) have not been demonstrated to be killing people in measurable quantity.