Comparative analysis of selective fungal culture media and incubation conditions for <i>Aspergillus fumigatus</i> in cystic fibrosis sputum

ABSTRACT Aspergillus fumigatus detection in respiratory samples of people with cystic fibrosis (CF) is important for the diagnosis of Aspergillus -related lung disease. Yet, fungal culture approaches are not standardized for clinical CF respiratory samples. We analyzed CF sputum to determine culture conditions that may improve the detection of Aspergillus fumigatus . A total of 281 remotely collected sputum samples from 74 adults with CF were analyzed in two laboratories, Johns Hopkins and Dartmouth. Aspergillus fumigatus was found in 121 (74%) and 84 (71%) samples in Johns Hopkins and Dartmouth, respectively. In the Johns Hopkins laboratory, we observed a decreased odds for Aspergillus fumigatus growth when using Czapek-Dox agar (adjusted OR [aOR] 0.78, 95% CI 0.68–0.89, P &lt; 0.01) compared to inhibitory mold agar. An incubation temperature of 30°C compared to 37°C was associated with decreased Aspergillus fumigatus positivity in 21%O 2 (aOR 0.71, 95% CI 0.58–0.88, P &lt; 0.01). We also observed 82% increased odds for Aspergillus fumigatus isolation while incubating in 37°C 1% oxygen (O 2 ) compared to 37°C 21% O 2 5% carbon dioxide (CO 2 ) (aOR 1.82, 95% CI 1.41–2.36, P &lt; 0.01). Additional work in the Dartmouth laboratory demonstrated Sabouraud agar media was associated with decreased odds for Aspergillus fumigatus positive culture compared to inhibitory mold agar (aOR 0.77, 95% CI 0.63–0.93, P &lt; 0.01). Our data suggest that use of inhibitory mold agar and 37°C and hypoxic incubation conditions may increase the odds to detect Aspergillus fumigatus in remotely collected CF sputa. Validation studies are needed to determine if these culture conditions improve A. fumigatus detection in CF. IMPORTANCE Aspergillus fumigatus is the most common filamentous fungus that affects the lungs of people with cystic fibrosis (CF), and the detection is critical to determine whether treatment is required. We examined how fungal culture media, sputum processing, and incubation conditions may impact the recovery of Aspergillus fumigatus in CF sputum. Our study found that semi-selective fungal culture media, such as inhibitory mold agar and incubation in 37°C and low oxygen, were associated with Aspergillus fumigatus growth in remotely collected CF sputum. Validation of our findings has the potential to impact the approach of clinical fungal culture to detect Aspergillus fumigatus in the CF population.