The Los Angeles Gay & Lesbian Center (Center) (defendant) was a nonprofit organization that provided medical services in Los Angeles County to the gay, lesbian, and transgender communities. The Center provided free testing and free treatment for sexually transmitted diseases. Between January 1999 and March 2004, the Center provided the wrong dose of penicillin to approximately 663 syphilis patients. When the Center learned this, the Center offered retesting and retreatment to all these patients. Some patients (plaintiffs) sued the Center and sought to certify a class of all California residents who had received the improper dose. The Center argued that the class should be established through an opt-in procedure to protect the potential class members’ privacy. The trial court approved the class with an opt-out notice. The Center was ordered to turn over the patients’ names and contact information to the plaintiffs for the purpose of sending out the class notice. The trial court also issued a protective order restricting the use of medical information and requiring the parties to use a numbering system to refer to the class members in all public filings. The Center appealed to the California Court of Appeal.