Use of Selective Fungal Culture Media Increases Rates of Detection of Fungi in the Respiratory Tract of Cystic Fibrosis Patients

Abstract

The prevalence of fungi in the respiratory tracts of cystic fibrosis (CF) patients has risen. However, fungal surveillance is not routinely performed in most clinical centers in the United States, which may lead to an underestimation of the true prevalence of the problem. We conducted a prospective study comparing the rates of detection for clinically important fungi (CIF), defined as ,, and species and, in CF sputa using standard bacterial and selective fungal culture media, including Sabouraud dextrose agar with gentamicin (SDA), inhibitory mold agar (IMA), and brain heart infusion (BHI) agar with chloramphenicol and gentamicin. We described the prevalence of these fungi in an adult CF population. A total of 487 CF respiratory samples were collected from 211 unique participants. CIF were detected in 184 (37.8%) samples. Only 26.1% of CIF-positive samples were detected in bacterial culture medium, whereas greater rates of detection for fungi were found in IMA (65.8%; < 0.001), in SDA (at 30°C, 64.7%; = 0.005), and in BHI agar (63.0%; = 0.001). The prevalences of and species were 40.8% and 5.2%, respectively, which are greater than the nationally reported prevalence numbers of 20.4% and 1.9%. Selective fungal culture media and longer incubation periods yielded higher rates of detection for CIF in CF sputum samples compared with that detected in bacterial culture medium, resulting in an underdetection of fungi by bacterial culture alone. The prevalence of fungi in CF may be better estimated by using selective fungal culture media, and this may translate to important clinical decisions.

The myriad challenges of respiratory fungal infection in cystic fibrosis

“…The first investigation in the United States to apply selective fungal culture media to expectorated sputum from adults with CF carried out 12‐month prospective study and noted prevalence rates of Aspergillus spp. of 40.8%, Scedosporium of 5.2%, Exophiala 4.7%, and Trichosporon 3.3% . Figure demonstrates that the prevalence of filamentous fungi isolated using fungal selective media is similar across these recent studies …”

“…These findings were supported by a recent CF cohort study in the United States which compared selective fungal media to traditional bacterial culture for the identification of Aspergillus , Scedosporium , Trichosporon , and Exophiala species in adults with CF . Of the 184 samples identified with one or more of these fungal species, bacterial culture detected fungal species in only 26% of these samples, with three other fungal selective media having much higher recovery rates, from 63% to 65.8%.…”

“…of 40.8%, Scedosporium of 5.2%, Exophiala 4.7%, and Trichosporon 3.3% . Figure demonstrates that the prevalence of filamentous fungi isolated using fungal selective media is similar across these recent studies …”

“…The use of chronic oral antibiotics, and inhaled antibiotics, is associated with the isolation of fungi from sputum samples . In particular, chronic azithromycin therapy may be associated with increased risk for Aspergillus isolation …”

Aspergillus and progression of lung disease in children with cystic fibrosis

“…However, for other parts of the analysis, both BAL and sputum culture results were used, as ACFDR data relied mainly upon sputum cultures. Three of the eight sites did not use specific fungal media routinely for CF respiratory specimens, potentially limiting rates of detection 35. However, no site bias was found for culturing fungi.…”