Listeria - is it really that risky?

So you've been told by your LMC to avoid certain foods during your pregnancy to minimize the risk of contracting listeriosis, but your mother swears she ate whatever she wanted to during her pregnancy and YOU turned out okay.  What do you do? Who do you believe? When the pregnancy cravings kick in, it can seem really tempting to give in to just that one piece of sushi, or the occasional ham sandwich, after all, one can't hurt can it?
Probably not. Listeriosis is not as common as the food safety pamphlets would have you believe, for example in 2005 the Auckland District Health Board recorded only 8 cases of listeriosis, compared to more than 4000 cases of campylobacter and hundreds of cases of salmonella and giardia. But the problem with listeriosis is that if you DO contract it, the consequences can be dire for your baby.
For people with healthy immune systems, contact with the listeria bacteria isn't a big deal, it rarely causes illness. But during pregnancy the immune system operates at a lower level than normal, in part to stop our bodies rejecting our unborn babies, but another consequence of this is that we are more susceptible to infections, so if a pregnant woman comes in contact with the listeria bacteria, she is more likely to become ill with listeriosis.
In addition, it is possible for the listeria bacteria to cross the placental barrier to your baby even without it causing you any symptoms. You might not even know you have it, but it can cross the placenta causing miscarriage or stillbirth. So whilst the total risk of contracting listeriosis might be low, it is worth looking at that risk in the context of "what if?" It might seem like forever, but in reality your pregnancy is just a few short months, and if avoiding certain foods can minimize the risk to your baby, isn't that worth it?