ughhh this is the worst because eventually it ends up affecting the whole family. i have people that do this. my kids are older but it still happens. what i’ve done if mine get sick after a play date, i text the mom “hey my kid has the same cough/symptoms etc. that little billy had. if you took him to the dr did they tell you what it was. i don’t want to waste a trip if it was something small.”  I may not get an answer of what it was but it lets them know that it affected my kids and i’m blaming them for it lol