that seams to be a minimal amount. Many members last year, myself included, around these parts had a very long cold spell. Afterwords we all had cleansing material painted all over. We all rushed to the compuer and asked the same question you did. I wouldn't have been able to "count" the number of streaks as there were thousands on all of my hives, the snow , leaves or anything w/in 4 or 5 ft. All of my hives made it.
I am beginning to believe based on some reading and lectures that every hive has viruses, nosema and mites. If they are otherwise healthy and unstressed, usually not an issssue. When weakened, they can take over a hive and kill it. Also, hygenic bahaviour can help w/ many of these issues as well. Twenty streaks is not many.