Navigating Childhood Friendships & Health Concerns: A Parent's Perspective

Question
With all the diseases today, I have to ask this question to either relieve myself from stress or make it worse.  My 2 1/2 year old daughter has a friend with a seizure disorder and now a cyst in her throat.  My daughter does not attend a daycare but may be doing so this summer.  The other day her little friend took my daughter's lollipop and gave her hers.  It was too late for me to stop them from switching as it happened so quickly.  I wanted to panic but I knew it was too late.  If that wasn't bad enough, later in the day they swapped drinks.  This episode has driven me crazy worrying about if my daughter could have contracted anything serious from this.  Please let me know how concerned I need to be and what can be done.  I try to watch my child very carefully but without hovering over her or putting her in a glass bubble, I don't know how to stop some of these things from occurring.  Thanks for your time.

Answer
Please let me know how concerned I need to be and what can be done.
You do not need to be overly concerned especially if your child is not in classes or day care with mentally retarded individuals who as a group tend to harbor and spread parasitic diseases due to poor hand cleanliness. OK?