High-volume Sputum Culture for the Diagnosis of Pulmonary Aspergillosis

BACKGROUND: Improved diagnostics are needed for the management of invasive fungal infections. Standard sputum cultures have a low yield in the detection of mold. Conventionally only a fraction of the specimen is cultured. We studied the performance of high-volume cultures (HVCs) where the entire specimen is plated on Sabouraud agar (SA). METHODS: Specimens were collected at our center from January 2015 through February 2017. For conventional culture, sputum was homogenized by mixing with an equal volume of 0.1% dithiothreitol solution and diluted 500-fold in sterile water. Ten μL of the diluted specimen was cultured on SA (2 plates) and incubated at 37°C and 45°C for up to 5 days. For HVC, the entire undiluted specimen (up to 1 mL) was cultured on SA (up to 2 plates) and incubated at 30°C for up to 14 days. RESULTS: We studied 306 paired specimens that were collected for both conventional culture and HVC on the same day. A total of 139 patients with positive cultures had the following conditions: chronic pulmonary aspergillosis (58%), allergic bronchopulmonary aspergillosis/severe asthma with fungal sensitization (27%), Aspergillus bronchitis (9%), cystic fibrosis/bronchiectasis (6%). Aspergillus was recovered by HVC in 114 specimens that had no mold growth by conventional culture. The same Aspergillus species was recovered by both HVC and conventional culture in 50 paired specimens. For 142 specimens there was no Aspergillus growth by HVC (Penicillium spp. grew in 4). For two of the negative HVC specimens A. fumigatus grew by conventional culture. The following species were recovered by HVC: A. fumigatus (80%), A. niger (10%), A. flavus (3%), other (7%). Susceptibility testing (EUCAST standard) was performed for 127 isolates of A. fumigatus. Rates of antifungal resistance were as follows: itraconazole 28%, voriconazole 19%, posaconazole 28%, isavuconazole 32%, amphotericin B 8%. Pan-azole resistance was detected in 17%. If HVCs were not performed, resistance to at least one of the antifungals would have been missed in 18/37 (49%) of cases. CONCLUSION: The recovery rate of Aspergillus spp. is significantly higher for HVCs compared with conventional cultures and this can impact patient care. HVCs can be performed in any microbiology laboratory without the need for additional tools. DISCLOSURES: R. Rautemaa-Richardson, Pfizer, Astellas, Gilead Sciences, MSD, Basilea: Consultant, Speaker honorarium; M. Richardson, Pfizer, Astellas, Gilead Sciences, MSD, Basilea and Pulmocide: Consultant, Speaker honorarium