Not just majority of Americans, but the majority of ALL adults around the world! Is there a specific reason you had this test done; in other words, are you feeling sick?
From what it looks like you either have the EBV virus or have had it. Don't be alarmed though, because majority of American's have had this at one time or another. It is generally short term and complications are low from my understanding. Mine came back positive, but nothing was ever mentioned to me about it. I wouldn't worry about it unless the doctor thinks it is of concern.