Myright, I have a 4 month old and I work in health care too, so my thoughts are with you guys. As a parent there can be a lot of misplaced guilt involved when someone who is dependent on you becomes ill. Hopefully I'm not being patronizing/out of line by saying this but, as your wife may know, many people in the community have staph species (of which MRSA is a variant) growing 'harmlessly' in their noses. Please tell her not to beat herself up over it - ANYONE could have 'given' it to him or it could have been a bite etc.
Best wishes from Oz to your little one for a speedy recovery!