We're always getting letters home about headlice, threadworms and today foot and mouth disease. Last year it was winter vomiting knocking out whole schools.
You can also take your choice currently at ours from the 'ghastly stomach upset' or the 'terrible throat virus' doing the rounds just now.
I was never off sick from school (mind you, I had to be dead before my mum would keep me home) and I don't remember a single letter about any ailments.