I had purchased nucs from a commercial beekeeper who's combs likely were contaminated with EFB.

Right around the beginning of swarming, EFB flourishes. 

I noticed that the colonies which had those old nuc combs developed EFB again, and then spread the EFB to adjacent colonies.

The contagious nature of EFB had me treat all colonies in the apiary prophylactically.

OTC seems to do an excellent job at rapidly reversing EFB, so a colony will go from a bad situation to a very good situation (health) within a matter of, perhaps 1-2 weeks.

I was keeping my fingers crossed that the EFB would not return this year, but alas, it looks like the colonies found some old honey or maybe an old dead scale when I reversed the hive bodies and exposed them to the old comb that came with the nucs.

Now that I know EFB is here to return every year, I will need to be prophylactic in advance.

After the 14 day treatment period, colonies never seem to re-bloom EFB even under stressful conditions.  

The symptoms are obvious.  Yellow melting larva uncapped larva in a state of devastation - within a week the entire population of uncapped larva can become infected.  Within that same week, EFB will usually spread to colonies in a row.

The more hygenic colonies can generally clear out the larva, but the obvious brood break, and the occasional melting larva gives it away.

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