In the case of Donegal Mutual Insurance Co. v. Richard Baumhammers, the Supreme Court ruled that “when multiple injuries can be traced to a single proximate cause”, there is but one occurrence. This ruling — which adopted the cause as opposed to effects theory of occurrences — reversed the lower court’s holding that each of the defendant’s 6 shootings (which took place over several hours in 4 PA counties) was a separate occurence that triggered policy coverage.

http://www.courts.state.pa.us/OpPosting/Supreme/out/J-3-2007mo.pdf