Background: We dealt with the occurrence of an outbreak of Candida parapsilosis in a neonatal intensive care unit (NICU) in September 2020. There have been several reports of C. parapsilosis outbreaks in NICUs. In this study we describe our investigation into both the transmission route and the biofilm of C. parapsilosis. Methods: C. parapsilosis strains were detected in three inpatients and in two environmental cultures in our NICU. One environmental culture was isolated from the incubator used by a fungemia patient, and another was isolated from the humidifier of an incubator that had been used by a nonfungemia patient. To prove their identities, we tested them by micro satellite analysis. We used two methods, dry weight measurements and observation by electron microscopy, to confirm biofilm. Results: Microsatellite analysis showed the five C. parapsilosis cultures were of the same strain. Dry weight measurements and electron microscopy showed C. parapsilosis formed biofilms that amounted to clumps of fungal cells. Conclusions: We concluded that the outbreak happened due to horizontal transfer through the humidifier of the incubator and that the C. parapsilosis had produced biofilm, which promoted an invasive and infectious outbreak. Additionally, biofilm is closely associated with pathogenicity.

Background: A carbapenem-resistant Enterobacteriaceae (CRE) outbreak occurred in an advanced emergency medical service center [hereafter referred to as the intensive care unit (ICU)] between 2016 and 2017. Aim: Our objective was to evaluate the infection control measures for CRE outbreaks. Methods: CRE strains were detected in 16 inpatients located at multiple sites. Environmental cultures were performed and CRE strains were detected in 3 of 38 sites tested. Pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and detection of β-lactamase genes were performed against 25 CRE strains. Findings: Molecular typing showed the PFGE patterns of two of four Klebsiella pneumoniae strains were closely related and the same MLST (ST2388), and four of five Enterobacter cloacae strains were closely related and same MLST (ST252). Twenty-three of 25 CRE strains harbored the IMP-1 β-lactamase gene and 15 of 23 CRE strains possessed IncFIIA replicon regions. Despite interventions by the infection control team, new inpatients with the CRE strain continued to appear. Therefore, the ICU was partially closed and the inpatients with CRE were isolated, and the ICU staff was divided into two groups between inpatients with CRE and non-CRE strains to avoid cross-contamination. Although the occurrence of new cases dissipated quickly after the partial closure, a few months were required to eradicate the CRE outbreak. Conclusion: Our data suggest that the various and combined measures that were used for infection control were essential in stopping this CRE outbreak. In particular, partial closure to isolate the ICU and division of the ICU staff were effective.

Background: Many of the pathogenic bacteria and fungi found in hospital environments form biofilms, which allow them to persist in the environment for long periods, posing a risk of hospital-acquired infections. Although the pathogens within biofilms often have reduced levels of drug susceptibility, the efficacy of disinfectants routinely applied against planktonic pathogens must be evaluated against biofilms as well. Our objective in this study was to determine the efficacy of treatment using slightly acidic hypochlorous acid water and to compare the results with sodium hypochlorite when both were used to disinfect Candida parapsilosis biofilms. Methods: C. parapsilosis in the planktonic or biofilm state was treated with each disinfectant. The number of viable cells that remained was determined, and scanning electron microscopy (SEM) of the disinfectant-treated biofilms was performed. Results: Compared with sodium hypochlorite, in a shorter period of time, hypochlorous acid water completely killed not only planktonic C. parapsilosis but also C. parapsilosis in a biofilm that had been formed for 72 h. SEM showed that both disinfectants were effective in removing the C. parapsilosis biofilm to some extent. Conclusions: Slightly acidic hypochlorous acid water appears to be an effective disinfectant against C. parapsilosis both in suspension and in biofilms.

Routine identification of Corynebacterium species can be challenging and may complicate investigation of suspected healthcare-associated transmission. We investigated a suspected cluster of blood culture isolates routinely identified as Corynebacterium jeikeium and retrospectively evaluated similarly identified isolates recovered at our hospital. After three patients in a hematology ward had blood cultures yielding C. jeikeium within approximately one month in 2024, pulsed-field gel electrophoresis (PFGE), environmental sampling, and follow-up surveillance were performed. We subsequently reviewed all blood culture isolates routinely identified as C. jeikeium from 2019 to 2025. Ten isolates from 10 unique patients underwent long-read whole-genome sequencing (WGS). Species identity was assessed by average nucleotide identity (ANI) against type-strain genomes, and genomic relatedness by core-genome phylogenetic and pairwise genome analyses. PFGE showed indistinguishable patterns for two cluster-associated isolates. No environmental isolate was identified as Corynebacterium spp., and no additional temporally associated cases were detected. WGS identified all 10 isolates as C. macclintockiae and did not support a single-clone transmission event; the two isolates with indistinguishable PFGE patterns were closely related but not genomically identical. However, direct or indirect transmission between the corresponding patients could not be excluded. These findings support integrating epidemiological investigation, accurate species identification, and high-resolution genomic analysis when evaluating suspected healthcare-associated transmission involving members of the C. jeikeium complex.