Part I: Antibiotic Resistance (AMR) - Global and Local Epidemiology

1.4 Vancomycin-resistant Enterococci (VRE)

1. VRE were first reported in Europe in 1986. Since then, this resistant organism has spread throughout the world and has become a major nosocomial pathogen. Currently, Enterococcus faecium is the most important vancomycin-resistant species. In the United States and some European countries, vancomycin-resistant Enterococcus faecium (VREfm) has disseminated widely in the hospitals and old age homes. [34]

2. The first case of VREfm in Hong Kong was identified in 1997, involving a patient returning from the United States. From 1997 to 2008, VRE occurrences were sporadic, resulting in occasional small clusters (<5–10 cases) of nosocomial transmission. There has been no sustained transmission within our healthcare system. In the mid-2000s, two ad hoc studies revealed that VRE was carried by less than 0.1% of patients in high-risk areas. [35,36]

3. A prolonged outbreak of VREfm occurred in our public hospitals starting in 2011, but through the enforcement of directly observed patient hand hygiene and other infection control measures, the outbreak was successfully contained by 2015. During this period, a total of 4,060 new cases of VREfm were reported in local public hospitals. [37]

4. The resistance of enterococci to vancomycin is mediated by mobile genetic elements. The vanA gene is carried in transposon Tn1546, while vanB is encoded in Tn1547. These transposons are mobile and capable of spreading the resistant gene to other highly virulent organisms like S. aureus. Consequently, although VRE may have low pathogenicity, they can serve as a source of mobile resistance genes. [38]

5. Hospital outbreaks caused by VRE have been increasingly reported globally. Molecular epidemiology studies using multilocus sequence typing have revealed that this increase is linked to the dissemination of a specific genetic lineage of Enterococcus faecium known as clonal complex 17 (CC17). [38,39] Research indicates that CC17 has been circulating in U.S. hospitals since the early 1980s. [38] Currently, CC17 is the predominant clone associated with hospital outbreaks worldwide. [40–44] The prolonged VREfm outbreak in Hong Kong’s public hospitals from 2011 to 2015 also involved strains belonging to the CC17 lineage. [37]

6. While the majority of CC17 VREfm isolates are typically susceptible to linezolid, resistance to this antibiotic can develop through the acquisition of cfr and optr genes, or mutations in the chromosomal 23S rRNA gene. [42,45]