My son came close to us going to the ER. And he was 2 when he got it.
I *think* knowing the "tricks" to keeping a pukey kid hydrated will reduce your chances of actually ending up at her ER.
If you're not in daycare, your baby will be older when they catch rotavirus, too, probably. That seems to be the way it works from what I've seen, at least.
And I bet the one in 100 number is an overestimations that takes into account those parents who just run to the ER over everything, too. If you don't expect rotavirus to be "bad" and don't know the symptoms, and the signs of actual dehydration, I can see a lot of people just going to the ER thinking their kid has some fatal disease after a few days of it.
My wild guess would be that a bf'ed kid not in daycare has a one in 300 chance of actually needing IV fluids because of rotavirus.