Fungal cultures in patients with allergic fungal rhinosinusitis: improving the recovery of potential fungal pathogens in the Canadian laboratory.

BACKGROUND There is no uniform consensus on how to grow fungi from sinus aspirates in the Canadian setting. Protocols vary between institutions, and the positivity rate for fungal cultures ranges between 10 and 20% even when endoscopically obvious allergic mucin is being sent to the laboratory. The aim of this study was to compare the occurrence of positive fungal cultures obtained by our institution's fungal culture method with the occurrence obtained by the Mayo Clinic's fungal culture method. The ultimate aim was to propose a modified, feasible, standardized protocol for culturing fungi from sinus aspirates in the Canadian laboratory setting. METHODS Twenty-five allergic mucin aspirates were collected in 23 consecutive patients meeting the clinical diagnosis of allergic fungal rhinosinusitis. These samples were sent to the microbiology laboratory, where half of them were subject to our conventional laboratory protocol and the other half to the modified Mayo Clinic protocol. RESULTS Positive fungal cultures were obtained in 16 of 25 (64%) specimens when the modified Mayo Clinic culture technique was used, with 12 cultures (48%) growing pathogenic fungus. Using our standard culture technique, 4 of 25 (16%) specimens resulted in a positive fungal culture, of which 3 grew pathogenic fungus (12%). A significantly greater fungal culture yield was obtained by the modified Mayo Clinic fungal culture technique than with our culturing technique. CONCLUSION The modified Mayo Clinic fungal culture technique, although more costly, is a highly sensitive and effective technique for growing fungi from nasal specimens when compared with our traditional culture technique.