Silent Outbreaks of Candida duobushaemulonii in a Pediatric Ward in Brazil

Background: While Candida auris is well known to cause hospital outbreaks, other species in the C. haemulonii complex are less well documented but gained attention as opportunistic pathogens. Only one documented outbreak has been published. We describe the second, silent, fungemia outbreak due to antifungal-susceptible C. duobushaemulonii. Methods: We retrospectively genotyped six C. duobushaemulonii bloodstream isolates, collected in a 4-month-period in 2022 (n = 4) and during a week in 2024 (n = 2) in pediatric patients in Brazil. Whole genome sequencing (WGS) was done and compared to n = 33 publicly available genomes, including four cases from an outbreak in Panama. Antifungal susceptibility was performed with the reference CLSI method. Results: MALDI-TOF-MS identified isolates as either C. pseudohaemulonii or C. duobushaemulonii albeit with low scores. ITS sequence analyses confirmed all isolates as C. duobushaemulonii. WGS proved the presence of an outbreak among four pediatric patients in 2022 and a genetically distinct cluster of two cases in 2024. All six isolates were susceptible to azoles and echinocandins and were interpreted as being resistant to amphotericin B with a MIC at breakpoint of 2 µg/mL. Conclusions: This study describes the second documented outbreak due to the rare yeast C. duobushaemulonii, belonging to the C. haemulonii species complex, during 2022-2024 in patients admitted to a pediatric oncology ward in a Brazilian hospital.