The NYtimes says frozen spinach is not implicated (right now)...
NY Times article

Another article I read said that cooked spinach should be heated to 160F to kill any bacteria, but right now they are recommending that people discard their spinach (what a waste...can it be composted?)

This morning's news said that bagged spinach with sell by dates between August and early October are what appear to be from the affected batch. I would guess that most frozen spinach had been picked, cooked and processed before that time. However some markets are pulling all spinach products, even dip (they don't want to chance any lawsuits).