J.A.
Two and 1/2 is an age where kids catch everything and anything regardless. So don't feel like you're not keeping up on the antibacterials and that he's sick because of it. He's going to get sick regardless. However, it's also a good time to start reminding him to keep the fingers out if his mouth. I found giving my 2 1/2 year old thumb sucker something to keep his fingers busy helped a lot. Little games made of paper, finger puppets (I drew on his fingers and he didn't want to 'eat the puppets'), things like that. Until the habit was "broken" - he still does it at night though.
Remember too, too much antibiotic material isn't good for kids, it's important for them to build immunities.
My advice, in short, keep tissues on hand and lots of nontoxic washable markers :)
Good luck.