Egg white safety?
For some reason I've always believed that all the bacteria lived in the yolk, but I know that's wrong. But anyways, while it is very unlikely that you're going to get salmonella, mixing 10 egg whites together, where just 1 bad one could spoil the bunch, as well as leaving them open for what is probably now 5 days, I wouldn't use it in anything that requires it to be raw. It's better not to take the risk. Next time, I'd suggest that you freeze them. Freeze like 2 egg whites per ice cube thing, and then store them all in a bag. Pretty convenient.
italian meringue is cooked by the hot sugar syrup, so don't worry about salmonella there. i would have no qualms about using 5 day old refrigerated egg whites for italian meringue. i have recipes for french macaroons where the advice is to leave the whites at ROOM TEMP for about that lomg....that i won't do!