We have unfortunately had to use the injection a number of times over the course of 11 yrs.  Our daughter has had diareaha, vomitting, lethargy from something like an ear infection, a stomach virus, a high fever that wouldnt go down, a broken leg, that sort of thing.  We were taught better be safe than sorry.  Our endo asks every visit if we have shot kits.  We keep a syringe, an alcohol pad, a bandaid, information on a small card about cah and the hydrocortone all in a small baggie with her name on a label on the front.  We have three set up like this so one can travel on overnighters, one stays in my purse/backpack and one stays at grandmas.  Your gut will tell you when you need to use it.  Good luck.