Varicella (chicken pox) is the prototype of "most infectious".
There is a famous case where a child on the 12th floor of a children's hospital, confined to his room, caught it from a child on the third floor, proven to be identical by molecular analysis.
Now, I read this on Twitter at 2 AM and I was up all night.
But I seriously doubt they have data that shows identity with varicella for transmissibility, and, as others have pointed out, "planted" is probably more correct than "leaked".
Very interesting - thank you!