Reviewed by Jen Cihlar, DO, Vanderbilt University Medical Center
Bottom line: Whole genome sequencing use in these outbreak studies has helped highlight the importance of fomite related spread, environmental cleaning, as well as raises future considerations regarding isolation practices, PPE precautions with rising rates of drug-resistant fungal organisms and their capacity for clinical harm.
Barbian and colleagues performed a 2-year outbreak study of 28 Candida auris cases in an academic tertiary care hospital burn ICU (BICU) from 2021-2023 in Illinois. Their original hypothesis was that there was likely spread from one continuous outbreak due to possible environmental reservoirs on the unit contributing to ongoing transmission. However, through retrospective review of patient data, admission screening and point prevalence surveys in the BICU, a thorough outbreak study, and utilization of whole genome sequencing, a different picture was painted. While several general infection prevention breakdowns were noted; correct use of personal protective equipment (PPE), hand hygiene (HH), especially in those who traveled about the hospital outside the BICU, environmental cleaning, especially of shared spaces and patient items seemingly no singular source link was identified between the cases.
Whole genome sequencing was performed on 22/28 case patients (79%) as well as on C. auris samples within the same hospital outside the BICU and other healthcare facilities within the medical system to estimate diversity of hospital isolates (N=80). Hospital isolates were compared to publicly available C. auris sequences from the state (n=364), revealing genomes from the BICU and related facilities were interspersed throughout other Illinois C. auris sequences which indicated multiple transmissions to the BICU facility from the broader diversity in the region. Sequencing also revealed 4 distinct BICU clusters and 7 distinct genotypes and that BICU clusters were very closely related among isolates within the cluster but not more closely related among clusters than for other regional isolates, consistent with multiple independent introductions from regional C. auris followed by within-unit spread rather than one contiguous outbreak spread from environmental reservoir on the unit.
While several limitations with this study exist the authors felt this study highlighted the importance of between unit transmission in addition to in-unit transmission and the roles of ancillary staff that move throughout the hospital during outbreaks.
In raising awareness for the capacity of non-C.auris Candida spp. to cause HAI outbreaks, whole genome sequencing was also utilized by Abdolrasouli and colleagues in their outbreak study of 3 clinical cases due to fluconazole resistant Candida parapsilosis (FR-CP) in a NICU nursery between May to July 2024. As part of the outbreak investigation, short tandem repeat (STR) genotyping performed showed all three isolates displayed the same STR genotype, suggesting clonal origin. Whole genome sequencing (WGS) revealed the isolates differed by two and five SNPs from each other, indicating clonality and confirming a single-source nosocomial transmission. Although no singular source of transmission was ultimately identified (some limitations with lack of significant environmental sampling) it was deemed spread was likely to related to breaches in standard infection control practices such as contaminated surfaces and lapses in HH as reported.
References:
Barbian HJ, Lie L, Kittner A, et al. Candida auris Outbreak and Epidemiologic Response in Burn Intensive Care Unit, Illinois, USA, 2021–2023. Emerging Infectious Diseases. 2025;31(3):438-447. doi:10.3201/eid3103.241195.
Abdolrasouli A, Curtis CM, Spruijtenburg B, et al. Cluster of clonal fluconazole-resistant Candida parapsilosis harbouring Y132F mutation in ERG11 gene in a neonatal ICU in the UK. J Antimicrob Chemother. 2025;80(3):887-890. doi:10.1093/jac/dkaf015
