In 2370, Verad, the unjoined Trill who briefly joined with the Dax symbiont (DS9 episode: "Invasive Procedures"), was sentenced to permanent residence at Gheryzan Hospital. After a year and a day, he was declared cured and allowed to leave. By 2372, however, Verad was apparently back at Gheryzan in a catonic state. In actuality, the person re-admitted as Verad was the former Duhan Vos, whose symbiont and identity both had been stolen by Verad.
That same year, Ziranne Idaris learned of the misuse of symbionts, and admitted herself to Gheryzan Hospital after having herself illicitly joined with the Roa symbiont. This brought the matter to the attention of her sister, Jadzia Dax, who uncovered the black market activities. (DS9 short story: "Reflections")