Discussion

VAIs constitute a risk factor for infection in patients undergoing hemodialysis. The pattern of microbes responsible for infection varies substantially among different types of access (25). Pooled data show that S. epidermidis accounts for most CVC-related infections, whereas S. aureus is more common in AVF- and AVG-related infections. In our study, staphylococcal species accounted for 58.67% of VAIs, with S. aureus being the most commonly implicated species, followed by CoNS and S. argenteus . In the 150 isolates collected from patients with VAIs, S. aureus was the predominant pathogen in AVG- and TCC-related infections, with a rate of 37/79 (46.84%) and 22/71 (30.99%), respectively. S. argenteus , another in SAC species, was also more predominant in AVG-related infections than in TCC-related infections. Notably, the nine S. epidermidis isolates were mainly collected from AVG-related infections (6/9); this finding is not consistent with those reported by a previous study (26), which indicated that improving sterilization management procedures during hemodialysis may reduce the number of skin clones such as S. epidermidis on TCCs. Regarding representative Gram-negative bacteria in VAIs, P. aeruginosa and BCC predominantly caused TCC infections; in particular, BCC caused only TCC infections.
In patients undergoing hemodialysis, S. aureus infection is common, especially MRSA infection, the incidence of which was reported to be higher than that observed in the general population by 100-fold (27). In our study, MRSA and MSSA infections accounted for 62.71% and 37.29% of S. aureus VAIs, respectively, with ST45, ST59, and ST239 being the predominant clones. Compared with our previous study,(4) the present study revealed that ST45, ST59, and ST239 were common in other diseases or surgical infections, indicating that these are major clones in our institution and warrant more attention. Notably, we also found the S. aureus ST239—an emerging multidrug-resistant MRSA clone worldwide that generally carries an SCCmec type III element—in methicillin-sensitive strains without mecA . Furthermore, a novel nonpigmented staphylococcal lineage that cannot be distinguished from S. aureus using routine microbiological identification methods is now formally classified as S. argenteus ; it was initially described as part of the distinct S. aureus CC (CC75) that is prevalent in aboriginal communities in the Northern Territory of Australia (28). S. argenteus comprising several CCs with many STs, especially ST2250, is the most commonly reported lineage with an extensive geographic distribution, including France, Belgium, Thailand, Taiwan, Japan, and China, indicating a global spread (29-35). The widespread S. argenteus has been isolated from both humans and animals. In our institution, ST2250 was the primary and only methicillin-sensitive ST revealed in VAIs, a finding that is consistent with those for previously reported S. argenteus -infected bacteremia cases in Taiwan (33).
The BCC is a group of opportunistic pathogens comprising at least 20 different species that commonly cause infections in immunocompromised patients, particularly those with cystic fibrosis (CF). B. contaminans was first identified from a contaminated Sargasso Sea DNA sample (36) and is increasingly associated with CF. However, other hospitalized non-CF patients have been reported to be affected byB. contaminans and B. cepacia infections. Nevertheless,B. contaminans has been found to be a contaminant in manufactured products, including pharmaceuticals and disinfectants (37, 38). In our institution, we obtained all BCC isolates from infected TCCs in hemodialysis patients with VAI; this suggests that the repeated use of mechanical device detergent and hemodialyzer reprocessing may cause contamination and that BCC species can survive in a harsh environment.
In this 5-year study, we collected 150 isolates from hemodialysis patients with VAIs and analyzed the isolates on the basis of the year of isolation (i.e., study period interval). Although the number of isolates from infected accesses was relatively low in the interval 2015–2018, the incidence of S. aureus , S. argenteus , and BCC infections increased by approximately 10% (i.e., 45.76%, 13.56%, and 13.56%, respectively). By contrast, CoNS and P. aeruginosainfections decreased by nearly 3%–5%. Previous studies have not addressed the spread or transmission of S. argenteus in the hospital environment (39). Nevertheless, the growing trend of S. argenteus in VAIs indicates the potential and importance of this novel, difficult-to-delimit species in healthcare-associated infections. Therefore, infection prevention and control measures that can be applied for S. aureus can be adopted for S. argenteus .