249. Limited Diagnostic Utility of Extended Aerobic Blood Culture Incubation for Fungal Pathogen Detection

BACKGROUND: Blood cultures are an important diagnostic tool for the detection of fungemia. At our institution, fungal blood cultures consist of aerobic blood culture with incubation extended from the standard 5 days to 14 days. Orders for fungal blood cultures exist in multiple electronic order sets for selected populations, including oncology and bone marrow transplant services. METHODS: To determine the yield of fungal blood cultures at our institution, a 570-bed tertiary-care referral center, we extracted all fungal blood culture results over a 4.5-year period (January 1, 2014–May 15, 2018) from a Laboratory Information System. RESULTS: Of the 21,657 fungal blood cultures performed, only 202 (0.9%) demonstrated growth and 189 (0.9%) grew fungal organisms. The majority (90%, n = 182/202) of positive fungal blood cultures grew a Candida or other yeast species. 96% (n = 174/182) of the fungal cultures that grew yeast would have been detected with standard bacterial blood culture. Eight of these cultures became positive during the extended hold period and grew a Candida species. All 8 cultures were collected from patients who had previous positive cultures for the same Candida species detected by standard incubation. Five fungal blood cultures from 4 patients turned positive after 5 days of incubation. Among these, two additional fungal pathogens were identified including 2 cases of Lomentospora prolificans and 2 cases of Fusarium. In both cases of L. prolificans and one case of Fusarium, the patients had previous positive blood cultures that detected the same organism with standard incubation. One patient with Fusarium had no previous positive blood cultures, but had multiple tissue cultures positive for Fusarium. The remaining cultures that turned positive after 5 days of incubation contained bacterial organisms, a number of which were considered clinically insignificant (e.g., Cutibacterium species). CONCLUSION: These data suggest that extended incubation of aerobic blood culture bottles has limited diagnostic utility beyond standard bacterial blood culture for detection of fungemia. Fungal blood cultures represent an opportunity for improved diagnostic test stewardship, and use should be restricted to selected situations in consultation with Infectious Diseases or Laboratory Medicine. DISCLOSURES: All authors: No reported disclosures.