Hi
I read your post this morning and wanted to say you are not alone and I understand how exactly you feel about this and perhaps share some things that have helped me. I almost didn't have children because of a fear of vomiting and pre-children any sign of sickness from anyone would have seen me make an emergency exit out of the building.
Of being a parent, it is the thing I absolutely dread and have spent many hours making myself hugely anxious about it. I did have hypnotherapy and I think that helped a bit. Or at least helped me get a bit of grip on myself. My mum had the same fear and weirdly so does her brother (my uncle) and I really wanted my kids to be free from it. The constant vigilence that it can induce is exhausting (checking for people looking ill on the train, avoiding getting too drunk, never taking the last tube home etc).
I realised the primary fear I have is that I will be sick and therefore if people are sick around me, it increases that likelihood. I have found when I am in the heat of the moment though when kids are ill, it's almost never as bad as I fear but it is the anxiety that it produces afterwards that I can't bear. My brain almost goes into crisis mode and I have a series of milestones for the next 76 hours when I am on constant high alert for other people getting ill. It's very lonely. People who don't have the fear, don't understand and because it is all very mundane to them, I often fear a sense of failure for being so ridiculous about it.
But the good news is that it is getting better/easier. I don't know why. Whether it is increased exposure I don't know but I do have sense that I almost got bored of feeling so rigid with fear about it. Now, that's not to say it's plain sailing but I am better at helping myself through it if that makes sense. My husband is good (though he still thinks I'm bonkers) and does help where he can. I make sure I am organised. I have packs of disposable rubber gloves, disinfectant and hospital grade wipes (ordered from amazon). I always take some on holiday and there are some in the car. If my girls get ill, they know the drill. They stay in bed until they are better (with iPad) and can now get themselves to the bathroom on most occasions.
I have realised that they won't always need me to do this, so it isn't for the rest of my life if that makes sense. I am now able to manage the clean-up (I don't trust anyone else to do as thorough) job and am very good at being encouraging and supportive from the bathroom doorway. If I can, I work from home for the few days after so I don't have to travel and if my mind spirals off, I try and distract myself as much as I can (being in the moment telling myself that right now, no-one is being sick and all is ok). watching TV that makes you laugh helps or reading a book you love. Puzzles, anything that brings you back to right now.
So far, my girls seem ok and quite calm if they are ill . They are nowhere as hysterical about it as I was at their age and I am hoping that as they get older it will happen less. I have realised that with good hand hygiene for all you can help prevent it spreading. I think if you can accept it, be kind to yourself about it and then ask yourself what would help and do what you need to do, it's a start. It's also really common I have realised so when you are standing in the school playground, I bet there is another parent who shares the same fear. I wish you all the best....