It is the time when the first infected person enters the bathroom from the time the door handle is in the non-infected state (it is assumed here that the individual will definitely touch the door when entering the bathroom)
It refers to the time when the first infected person enters the toilet since the door handle is not infected (here, it is assumed that the individual will contact the door when entering the toilet)
It is the time when the first infected person enters the bathroom from the time when the door handle is uninfected (here, it is assumed that the individual will definitely touch the door when entering the bathroom).