LAUSR

Dear Editor, Rhodotorula species, belonging to the family Sporidiobolaceae, are yeasts that are present in the environment and can cause opportunistic infections in immunocompromised patients [1, 2]. Among Rhodotorula species, only R. mucilaginosa, R. glutinis, and R. minuta have been reported to cause human infections [1, 2]. Rhodotorula sp. are mostly isolated from the blood of immunocompromised patients, where they cause fungemia or catheter-related infections. Only one case of pneumonia caused by R. mucilaginosa has been reported to date in an immunocompromised patient [3]. We report the first case of fungal pneumonia caused by R. mucilaginosa in an immunocompetent patient. The infection was confirmed by fungal ribosomal RNA (rRNA) sequencing using wedge-resected lung tissue. This case report was approved by the Institutional Review Board of Hallym University Dongtan Sacred Heart Hospital, Hwaseong, Korea (IRB No. 2020-03-017). A waiver of consent was granted due to the retrospective nature of this study. A 52-year-old man visited our hospital in July 2019 because of a pulmonary nodule found incidentally during a health check-up at a local clinic in May 2019. The patient did not have any underlying disease and his complete blood count was within the normal range. A lobulated nodular lesion measuring 3.5×1.6 cm was observed in the left lower lobe on radiological examination (computed tomography (CT); Fig. 1A). Serological screening tests for parasites (Clonorchis, Paragonimus, Cysticercus, Sparganum, and Toxocara) and the Aspergillus antigen (Galactomannan) test yielded negative results. Histopathological evaluation of a percutaneous needle biopsy revealed scattered, brown, oval, yeast spores (5–7 μm) and chronic granulomatous inflammation, leading us to suspect fungal infection (Fig. 1B) [4]. Fungal culture using needle biopsy tissue was not performed at that time. Empirical antifungal therapy with fluconazole 400 mg/day was initiated and continued for three months (Aug 14–Nov 23, 2019), because cryptococcal infection was suspected based on the histopathological findings. During antifungal treatment, CT revealed a slight decrease in nodule size (2.6×1.6 cm), which increased (to 3.1×1.9 cm) three months after discontinuation of the antifungal therapy. Wedge resection of the lung lesion was performed for definite diagnosis and treatment on March 5, 2020, and the fresh specimen was partitioned and sent for histopathological evaluation, fungal culture, and fungal rRNA sequencing. The histopathological features of the wedge-resected lung tissue were similar to those of the previous needle biopsy specimen.