Here in SC I know 3 of us had the exact same symptoms.  Clemson university tested for EFB but came back negative even though it appeared to be. I found a Vet that wrote me a directive for Terrimycin and I treated all the yards that had these symptoms.  It cleared up fast and the hives bounced back and built up as nothing was ever wrong. I figured a bacterial infection of some sort. This was in early March and haven't had a reoccurrence yet. I had low mite counts in late fall and early spring. The queens were from 4 different breeders. 

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