>It it my understanding that EFB is almost always present,  but only develops into an issue under the right conditions.  The antibiotic allows them to get it back under control.

In the UK a survey found that Mellissococcus  plutonius bacteria were not ubiquitous as had been suggested.  It may be present as an inapparent infection in some colonies which then go on to develop EFB symptoms when conditions are favourable - usually when the spring flow starts and the ratio of nurse bees to larvae is reduced because more bees are recruited to foraging.  The symptoms can then disappear when the flow stops.  For this reason it has been called the disappearing disease.

The use of OTC, the method of choice for many years in the UK if the colony was not to be destroyed (an option offered if the colony was strong) has not proved to be very effective over the years with, from memory, a recurrence of 27% in the following year.  In recent years there has been a move to the use of the shook swarm - bees shaken down into a clean hive with foundation, excluder under the brood box for a week so that they do not abscond, feed heavily after a couple of days.  (Full description here:
www.nationalbeeunit.com/downloadDocument.cfm?id=203).
I believe that this has reduced recurrence to around 4%.

Best wishes

Peter 
52°14'44.44"N, 1°50'35"W

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