# Results from the Survey of Antibiotic Resistance (SOAR) 2020–21 in Vietnam: data based on CLSI, EUCAST (dose-specific) and pharmacokinetic/pharmacodynamic (PK/PD) breakpoints

## TL;DR

This study reports antibiotic resistance rates in Vietnam for two common respiratory infection-causing bacteria using multiple testing standards.

## Contribution

The paper provides new antibiotic susceptibility data for S. pneumoniae and H. influenzae in Vietnam using CLSI, EUCAST, and PK/PD breakpoints.

## Key findings

- High rates of penicillin-resistant S. pneumoniae and BLNAR H. influenzae were observed.
- Susceptibility to amoxicillin and ceftriaxone varied significantly between CLSI, EUCAST, and PK/PD breakpoints.
- H. influenzae showed high fluoroquinolone susceptibility (88.0%–89.0%) under CLSI criteria.

## Abstract

Antibiotic susceptibility determination of Streptococcus pneumoniae and Haemophilus influenzae from community-acquired respiratory infections collected in 2020–21 from two hospitals in Ho Chi Minh City, Vietnam.

MICs were determined by CLSI broth microdilution; susceptibility was interpreted based on CLSI, EUCAST and pharmacokinetic/pharmacodynamic (PK/PD) breakpoints.

A total of 144 S. pneumoniae and 191 H. influenzae isolates were collected. S. pneumoniae susceptibility to amoxicillin and amoxicillin/clavulanic acid (2:1) was 56.9% and 56.3% (CLSI), 29.2% and 25.7% (EUCAST high-dose) and 78.5% using high-dose amoxicillin (4 g/0.25 g/day, PK/PD). Susceptibility to ceftriaxone was 91.7% by EUCAST (high-dose) and 50.7% by CLSI or PK/PD. Pneumococcal cefotaxime susceptibility was 61.8% by CLSI (29.9%, EUCAST). Penicillin susceptibility was 69.4% by CLSI intravenous/EUCAST high-dose, but 6.3% using CLSI oral/EUCAST low-dose breakpoints. Tetracyclines, macrolides and trimethoprim/sulfamethoxazole had 5.6%–16.7% susceptibility.

Among H. influenzae isolates, 59.7% were β-lactamase-negative, of which 87.7% and 74.6% were ampicillin-resistant (BLNAR) following EUCAST and CLSI criteria, respectively. H. influenzae fluoroquinolone, macrolide and tetracycline susceptibility reached 62.0%–89.5% (CLSI, EUCAST); macrolide susceptibility was 3.7%–5.8% (PK/PD). All were susceptible to ceftriaxone (all breakpoints) and cefotaxime (CLSI, PK/PD); cefotaxime susceptibility was 15.7% by EUCAST. H. influenzae amoxicillin/clavulanic acid susceptibility was 45.5% (EUCAST) and 32.5% (CLSI) but increased to 82.8% with high-dose (4 g/0.25 g/day, PK/PD).

The hospitals showed high rates of penicillin-resistant S. pneumoniae and BLNAR H. influenzae. S. pneumoniae showed low susceptibility to macrolides and several cephalosporins. H. influenzae fluoroquinolone susceptibility was 88.0%–89.0% (CLSI). Future surveillance across Vietnam will help understand susceptibility trends over time and regions.