in fact, Irie also said "this stage", so it is 100% sure it isn't the disease itself ^^
and well, considering the various confirmation of both spoiled and gamer parties, no worry about it.
that said, the name of the disease is really not a critical information
EDIT: "Satoko-chan LEVEL 3 desu". (there is maybe a particle after "chan", but i way cannot confirm this)
looks like the missing word is implied, since Rika already knows about it as well. (that can be translated as "Satoko-chan's ... is level 3"). that said, the "stage" mention after this is self explanatory.
oh well