What are the prerequisites for class treatment of medical monitoring claims?

We have not previously addressed the prerequisites for class treatment of medical monitoring claims. "Section 382 of the Code of Civil Procedure authorizes class suits in California when `the question is one of a common or general interest, of many persons, or when the parties are numerous, and it is impracticable to bring them all before the court.' The burden is on the party seeking certification to establish the existence of both an ascertainable class and a well-defined community of interest among the class members." (Washington Mutual Bank v. Superior Court (2001) 24 Cal.4th 906, 913, 103 Cal. Rptr.2d 320, 15 P.3d 1071 (Washington Mutual).)³