> We examined honey bee, Apis mellifera L., colonies pollinating almonds in California during February 2003 for Paenibacillus larvae subsp. Larvae, the causative organism of the virulent brood disease American foulbrood. Of the 570 colonies sampled, 33.3% were found positive for P. larvae larvae spores. Our conservative estimate of a disease equivalent ... indicates that 3.86% of colonies had an active infection. 

> We have encountered operations with unexpectedly high levels of American foulbrood (AFB). We suspected that AFB levels rose along with the emergence of oxytetracycline (terramycin) resistance in the late 1990s and perhaps was aggravated by declining honey prices, which resulted in fewer colony inspections.   

> High spore counts were found in 3.89% of surveyed commercial colonies. Based on this information, we project that 28,799 colonies had 1 disease equivalent number or more of P. larvae larvae CFUs. If a 15% error factor is included, the number rises to 33,118 colonies. Many, if not most, of these colonies probably had active cases of AFB. Others not exhibiting AFB, but with high or moderately high spore levels, suggest that prophylaxis must be used to avoid disease outbreaks.

Eischen, F. A., Graham, R. H., & Cox, R. (2005). Regional distribution of Paenibacillus larvae subspecies larvae, the causative organism of American foulbrood, in honey bee colonies of the western United States. Journal of economic entomology, 98(4), 1087-1093.
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