The genus Vanrija was initially characterized by Moore with Vanrija humicola designated as the type species [1,2]. Comprising basidiomycete fungi within the Trichosporonaceae family, Vanrija is widely distributed in the environment but an oppotunistic pathogen in severely debilitated hosts [3]. Among the nine recognized Vanrija species [4], V. humicola has previously been referred to as Cryptococcus humicola, Candida humicola, Cryptococcus humicolus, Torula humicola, Apiotrichum huicola, Azymoprocandida humicola, Mycotorula humicola, or Asterotremella humicola [5]. There is fewer than 10 cases published [2,3,6–9]. Systemic infections of V. humicola occur in immunocompromized hosts, such as central nervous system infections in human immunodeficiency virus (HIV) infected patients or cancer patients in literatures [9]. Until now, the only two reports regarding on urinary isolates were reported available in English [6,10], and there is still no report on a human infection in Korea. At our hospital, a tertiary care hospital in Seoul, Korea, V. humicola has been infrequently detected since it first appeared in 2021. This study therefore aims to elucidate the clinical significance of V. humicola isolated at our hospital.

Since 2016, a total of four cases of V. humicola identified to species-level using MALDI Biotyper (Bruker Daltonics, Bremen, Germany) were recovered from urine culture. The clinical characteristics of the patients with V. humicola were retrospectively reviewed through electronic medical records. Clinical relevance of V. humicola were evaluated with pathogenicity, infection types, risk factors of acquisition and epidemiological linkage between the cases. This study was approved by the Institutional Review Board of Asan Medical Center (No. 2024-0049) and the requirement for informed consent was waived. Two recent isolates were subcultured on blood agar plate (BAP), potato dextrose agar, and Sabouraud dextrose agar (SDA) plate and colonial and microscopic growth was observed with incubation at both 25℃ and 37℃. Phenotypic tests were performed using the VITEK2 YST (bioMérieux), API 20C AUX (bioMérieux) and urease test tubes. Sequence analysis was carried for the internal transcribed spacer and D1/D2 regions of the 26S ribosomal DNA. Antifungal susceptibility test was performed using the Sensititre YeastOne YO10 AST (Thermo Fisher Scientific) with visual reading after 48 hours of incubation at 25℃.

All four cases recovered V. humicola from urine cultures after hospitalization for 14-100 days due to serious underlying and comorbid diseases. None of them did not cluster during hospitalization (Table 1). All except one showed symptoms or signs of cystitis as well as urine cultures produced pure culture of V. humicola > 100,000 CFU/mL. A man with a traumatic esophageal rupture had 3,000 CFU/mL of V. humicola isolated from his urine, and the urine analysis was normal, suggesting that he was colonized with V. humicola. The other three were immunocompromized, of whom two were with cancer chemotherapy and one with pancytopenia and prednisolone treatment. Two indwelled foley catheter for 24 and 45 days, respectively, and developed hematuria. Although one patient received voriconazole due to Candida krusei isolated from mediastinitis sites, the only patient to receive antifungal treatment targeting V. humicola infection was an 86-year-old man with pancytopenia who received 60 mg prednisolone daily for 25 days. The patient was empirically treated with 50 mg caspofungin for three days, but died 4 days after isolation of V. humicola, before the species identification was reported. Three remaining patients were discharged with resolution of chief complaints without any treatment targeted for V. humicola (Table 1).