# Rising burden of enterococcal bacteremia in Victoria, Australia: population-based incidence and antimicrobial resistance trends from three decades of surveillance

## TL;DR

This study tracks the rise of enterococcal bacteremia in Victoria, Australia, over 35 years, showing increased cases and high resistance to vancomycin.

## Contribution

The study provides long-term population-based incidence and antimicrobial resistance trends of enterococcal bacteremia in Victoria.

## Key findings

- Enterococcal bacteremia incidence increased from <3 per 100,000 in 1988 to >10 by 2022.
- Vancomycin resistance in E. faecium ranged from 50.7% to 66.5% over the past decade.
- Statistical modeling improved the accuracy of incidence estimates despite inconsistent hospital participation.

## Abstract

Enterococcal bacteremia is a common healthcare-associated infection, associated with significant morbidity and mortality, with the emergence of vancomycin-resistant enterococci further complicating treatment and clinical outcomes. Despite this, long-term estimates of population-based incidence and antimicrobial resistance trends are limited. We aim to describe the burden of enterococcal bacteremia in Victoria, Australia (population 7.0 million), over a 35-year period. We conducted a retrospective analysis of laboratory-confirmed enterococcal bacteremia episodes voluntarily reported to the Victorian Hospital Pathogen Surveillance Scheme database from 1988 to 2022. Population-based incidence was estimated using inverse probability weighting to adjust for inconsistent hospital participation. Incidence per 10,000 hospital admissions was determined for the period 2011–2022. Antimicrobial resistance was calculated as the annual proportion of resistant isolates among all tested isolates. Overall, 11,157 enterococcal bacteremia episodes were identified, mainly Enterococcus faecalis (n = 6,915, 61.9%) and Enterococcus faecium (n = 3,558, 31.9%). Incidence increased from <3 episodes/100,000 population in 1988 to >10 by 2022. Incidence per 10,000 hospital admissions within Victoria has also increased from 2.8 in 2011 to 4 in 2022. Although E. faecalis remained mostly susceptible to tested antibiotics, E. faecium showed persistently high levels of vancomycin resistance, ranging from 50.7% (n = 69/136) to 66.5% (n = 139/209) over the past decade. Increasing incidence and high rates of vancomycin resistance among E. faecium highlight the ongoing clinical and public health challenge posed by enterococcal bacteremia. Applying statistical modeling to account for variability in hospital participation improves the certainty of incidence measures and strengthens the evidence for true increase in disease burden.