Is this truly heated enough to kill all potential bacteria where you would feel safe giving it to those in certain riskier groups?  What about using meringue powder in place of the egg whites?  Has you tried this and what are your thoughts?

I use pasteurized eggs if I'm offering it to the public.

http://cakecentral.com/t/661186/can-someone-tell-me-about-italian-buttercream-is-it-safe

The syrup definitely heats the egg mixture enough to kill bacteria, but if you're particularly concerned, you could opt for a SMBC instead.  Whisking the egg/sugar mixture over the double-boiler until it's uniformly hot to the touch always makes me more comfortable.

FDA says to cook eggs to 160F http://www.fda.gov/food/resourcesforyou/Consumers/ucm077342.htm If you test the temperature of your meringue after you've added the hot sugar syrup it WON'T reach that temperature. I've tested it before and I can't remember what it did reach but I know it wasn't that hot. I now exclusively use SMBC, I actually find it a lot easier to make now and I can make larger batches after investing in a decent stainless steel bowl.

I had read that IMBC was more stable at hotter temperatures than SMBC which is why I was leaning that way.  What about heating the sugar syrup a lot higher before adding it to the meringue?  Has anyone used the wilton meringue powder in place of egg whites in this and had good results?  Thank you for everyone's input.

It's been a debate as to if the hot syrup gets the egg whites to the safe temperature or not. In this thread a member did make SMBC with meringue powder. I don't know if it was Wilton brand.

http://cakecentral.com/t/586008/imbc-okay-with-meringue-powder-instead-of-actual-egg-whites/15

I also saw some recipes online that used mp to make IMBC with good results. I never thought about using meringue powder in IMBC or SMBC icings until you posted. Hmmmmm, it might be a good alternative opposed to buying pasteurized egg whites