ER visits while immunosurpressed

My 4 year old son has a pretty bad cold right now but is acting normal and up until last night he was not running a fever.  We have to keep a close eye on him with colds since he has asthma and the colds can activate the asthma and if that happens we sometimes have to take a trip to the ER which is scary since not only is my baby sick but I'm immunocompromised from medications.

Last night, my poor son had a febrile seizure from spiking a fever, so immediately I ran him to the nearest pediatric ER.  Each time I have to enter the ER it is dangerous since I can pick up anything immediately but as his mother there is no one else that I will allow to take him, including his dad.  While there I completely forget about me and my concerns; my focus is completely on him but they come back when we are home and he is OK.

Somehow, I can pick up any cold or stomach flu going around just by going to the mall but can go to the ER where there are all of these sick people and come out with never catching anything.  How does that happen?  Is someone looking out for the sick mommies out there?  I have no idea but I've decided to stop questioning that and just have faith that all will be OK.