We just returned from a cruise where we went the document of recovery route with our 4 year old. We had both the positive test and a letter from her doctor to be safe because I had read many people saying the letter was required even though carnivals website says you only need the positive test. I gave them only the positive test first without even mentioning the letter to see if they take it, and the rep said he needs a letter from the doctor. So I gave him the letter and he cleared us to cruise. I probably could have made a case saying that’s not what the website says, but who knows where it would have gotten me, so I definitely recommend bringing a letter from the doctor to be safe.