Not only can people be carriers but also dogs from an aricle I read. I always
ran toothbrushes throught the dishwasher when on of my 5 got sick and I also
had each of them pick a different colored cup to use when they were small, so that they would not drink from the wrong cup and get sick.
I also agree with boosting his immune system. My neighbors son had to get
his tonsils out due to repeated infections. He grew 3 inches the year after
they came out and he wasn't sick once the year after!