Apparently, ham off the bone has to come from Australia, due to quarantine laws.
So ham off the bone, cut fresh after eating should be ok. I would only eat ot that day though - but it's your choice.
Listeria does grow and multiply at refrigeration levels (1 - 4 degrees Celsius)
If you want to be extra paranoid, then stick your leg of hammy goodness in the oven with a yummy glaze first and heat through then enjoy all of that yummy goodness!
At the end of the day, it is a personal choice by the individual mother. The risks are very real, they do exist, even if they are tiny. I ate ham from a regular deli that I always eat it from and no harm came to me. Maybe I was just lucky. It is all up to you what risks you choose to take. There is risk from eating anything really.