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UBC Theses and Dissertations

Efficacy of composting to decontaminate Cryptococcus gattii-colonized plant waste Ge, Bin


Cryptococcus gattii is a human fungal pathogen that emerged on Vancouver Island, BC in 1999. This study aimed to investigate C. gattii survival in composting systems and occupational exposure to C. gattii in work tasks associated with composting. The presence of C. gattii was monitored in composting feedstock and product for one calendar year in a municipal composting facility in Cumberland, BC. Additionally, the survival of an environmental C. gattii isolate was tested in a composting experiment conducted with custom-designed composters that simulated in-vessel composting and home backyard composting. Potential inhalation occupational exposure to C. gattii while performing composting-related tasks were measured during residential yard waste chipping by city workers in Parksville, BC and during the composting experiment where C. gattii contaminated feedstock was composted. C. gattii persisted through three out of five in-vessel composting trials despite high composting temperatures (mean > 60ºC, peak 85ºC) which were achieved evenly throughout the composting material for long periods (> 65 hours). C. gattii was also detected in one out of two yard composting trials after 60 days of composting. The year-long composting feedstock and compost monitoring for C. gattii returned no positive samples. Air sampling during composting-related work tasks found no detectable level of C. gattii. Current composting standard and practice in BC are unlikely to be adequate in eliminating C. gattii from contaminated composting feedstock. Based on the results of this study, the risks of occupational exposure to C. gattii during residential yard waste chipping and composting of contaminated material are low.

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