Assessment of worker exposure to airborne molds in honeybee overwintering facilities.

Airborne fungi in honeybee overwintering and equipment cleaning facilities were enumerated and identified to determine worker exposure during cleaning and routine beekeeping operations. Testing was prompted by observations of extensive mold growth on dead bees and associated material and by results of a preliminary study at one Alberta beekeeping facility that showed very high numbers of mold colonies on air samples taken during worker activity. To evaluate whether high mold counts were indicative of a problem at a single site or were industry wide, approximately 120 air samples were collected with a Reuter centrifugal sampler inside 10 overwintering facilities before and during routine beekeeping activity during fall, winter, and spring periods. A set of 30 samples was collected from 15 sites used for annual equipment cleaning. This study showed that average spore counts per overwintering site ranged from 238 to 1442 colony-forming units (CFU)/m3 prior to disturbance by workers and from 2200 to 13,931 CFU/m3 while workers swept up dead bees. Levels of airborne molds recovered during annual cleaning of beekeeping equipment ranged from 300 to 54,700 CFU/m3 with an average of 16,083 CFU/m3. Potentially toxigenic, pathogenic, or allergenic molds were recovered at all sites. Since the data indicate that exposure to high levels of airborne molds is widespread throughout the industry, actions that might help minimize worker exposure are discussed.