An injury may be either: (a) "specific," occurring as the result of one incident or exposure which causes disability or need for medical treatment; or (b) "cumulative," occurring as repetitive mentally or physically traumatic activities extending over a period of time, the combined effect of which causes any disability or need for medical treatment. The date of a cumulative injury shall be the date determined under Section 5412.
Ca. Lab. Code § 3208.1