Five patients with B. capitatus infections were observed at 3 tertiary care hospitals in Switzerland during June 2009–June 2011 (Table 1, Table 2). These hospitals provide services to a population of ≈3 million persons living in the temperate zone north of the Alps in an area ≈5,000 km². A structured chart review was conducted for each patient, and further information was obtained from the involved infectious diseases specialist. The yeast was identified by using standard culture methods (Sabouraud dextrose agar with chloramphenicol and gentamicin and corn meal agar Tween 80; both from Oxoid, Cambridge, UK) and ID 32 C (bioMérieux, Marcy l’Etoile, France) (13). Identification of isolates was confirmed by DNA sequence analysis of the intergenic spacer (ITS) region (primers ITS1 + ITS4, GenBank accession nos. HQ014711.1 and HQ014712.1). For antifungal drug susceptibility testing, a microtiter broth dilution method based on the Clinical and Laboratory Standards Institute M27-A2 standard (Sensititre YeastOne; TREK Diagnostic Systems, East Grimstead, UK) was performed. Disk diffusion testing of fluconazole and voriconazole was performed as described (10). A review of the microbiology laboratory records of the 5 Swiss university centers yielded no additional isolations of B. capitatus in the past 5 years.

Patient 1 was a 66-year-old man with secondary acute myeloid basophilic leukemia. He became febrile, and pulmonary nodules and pustular skin lesions developed after induction chemotherapy. Blood cultures and cultures from a skin lesion yielded B. capitatus. The patient was treated with amphotericin B and voriconazole, both of which had low MICs. Skin lesions improved within days, and pulmonary nodules resolved within weeks. Eventually, relapsing leukemia proved refractory, and the patient died of multiorgan failure.

Patient 2 was a 68-year-old woman with acute myeloid leukemia. Neutropenic fever developed after induction chemotherapy. Blood cultures yielded B. capitatus. She was treated with liposomal amphotericin B and voriconazole. However, she died of multiorgan failure 9 days after diagnosis.

Patient 3 was a 58-year-old man receiving induction chemotherapy for acute myeloid leukemia, who was treated for polybacterial neutropenic sepsis. Caspofungin was added because of persistent fever. B. capitatus was isolated from blood cultures, urine, and tracheobronchial fluid while he was being treated. Antifungal therapy was switched to liposomal amphotericin B and voriconazole. When a preliminary report indicated an amphotericin B MIC >2 µg/mL (Etest; bioMérieux) for the isolate, treatment was changed to fluconazole. Multiorgan failure occurred, and he died 15 days after diagnosis. Autopsy findings confirmed extensive fungal pulmonary infiltrates with angioinvasion and multiple foci of B. capitatus infection in the liver, spleen, kidneys, bone marrow, myocardium, and brain.

Patient 4 was a 60-year-old man who was receiving continuous ambulatory peritoneal dialysis for renal failure 15 years after kidney transplantation for chronic glomerulonephritis; he sought care for acute peritonitis. Upon cultivation of yeasts in the dialysis fluid, caspofungin was started and changed to voriconazole when B. capitatus was identified. The patient’s symptoms rapidly improved, and voriconazole was discontinued after 4 weeks.

Patient 5 was a 56-year-old woman who underwent combined pancreas–kidney transplantation because of diabetic nephropathy and pancreatic insufficiency in December 2010. Two months later, B. capitatus was cultivated in urine while she was being treated empirically with caspofungin for possible fungal infection. Emphysematous cystitis was detected by computed tomographic scan, and B. capitatus was cultured from urine collected from the right kidney. Despite treatment with voriconazole, B. capitatus was cultured from urine for several weeks; however, the patient recovered.

The repeated isolation of B. capitatus in a temperate climate zone was unexpected because of the well-documented restriction of B. capitatus to areas with a Mediterranean climate >450 km south in Italy, Spain, and France. Because of the high recovery rate of the organism from blood cultures of patients with disseminated infection and the ease of culturing B. capitatus on standard media, we believe it unlikely that a large number of cases could have been missed in the past.

Central Switzerland has witnessed a steady rise in temperatures since the mid-1980s. Mean annual temperatures for the past 25 years were all above the mean for 1961–1990 and now exceed those of 1980 by >1°C. The rise in average temperatures was more pronounced during spring and summer months. Since 1981, average spring and summer temperatures in central Switzerland have increased by 0.77°C and 0.48°C per decade, respectively (14).

The occurrence of 4 of the 5 infections reported here during the warm season indicates that the rising temperatures might have contributed to the expanded range of climatically restricted fungi to cooler areas and that the emergence of B. capitatus might be a consequence of the local effects of global warming (5,15). Alternatively, importation of the pathogen from areas to which it is endemic through increasing traffic of humans and goods might have led to establishment of a new endemic hotspot. Our observation should alert clinicians caring for severely immunocompromised patients in temperate areas to consider infections caused by unfamiliar fungal pathogens, notably B. capitatus.