Contact tracing was a method of monitoring a disease's spread by determining who infected persons came in contact with.
In 2259, contact tracing aboard USS Enterprise identified La'an Noonien-Singh's sharing of a turbolift with a light virus-afflicted Ensign Lance as being a possible source of her infection. Later, Christine Chapel noted that contact tracing was hit and miss, as some patients were catching it from nearby infected, while Cadet Nyota Uhura hadn't caught it despite having infected roommates. (SNW: "Ghosts of Illyria")