Results from the Survey of Antibiotic Resistance (SOAR) 2018–21 in Italy and Spain: data based on CLSI, EUCAST (dose-specific) and pharmacokinetic/pharmacodynamic (PK/PD) breakpoints

Objectives: To determine the antibiotic susceptibility of community-acquired respiratory tract infection (CA-RTI) Streptococcus pneumoniae and Haemophilus influenzae isolates from Italy and Spain, 2018-21. Methods MICs were determined by CLSI broth microdilution, and susceptibility data were interpreted using CLSI, EUCAST and pharmacokinetic/pharmacodynamic (PK/PD) breakpoints. Results: A total of 77 S. pneumoniae and 249 H. influenzae were collected from Italy and 176 S. pneumoniae and 275 H. influenzae from Spain. Approximately 65% of pneumococci were penicillin-susceptible by CLSI oral or EUCAST low-dose breakpoints; by EUCAST high-dose or CLSI intravenous administration, 92.2%/95.5% (Italy/Spain) were susceptible. In Italy, 71.4% to 89.6% susceptibility (CLSI) was observed to amoxicillin/clavulanic acid, amoxicillin and most cephalosporins. Cefaclor, tetracyclines, macrolides and trimethoprim/sulfamethoxazole were less active against Italian (51.9%-67.5% susceptible) versus Spanish (67.0%-81.2% susceptible) isolates. The most potent antibiotics were fluoroquinolones (≥99.4%, excluding EUCAST low-dose). Most H. influenzae isolates were β-lactamase negative with a few ampicillin-resistant isolates (CLSI: 0.5% Italy, 3.1% Spain). Rates of β-lactamase positivity were 14.1% (Italy) and 17.1% (Spain). Susceptibility was >90% (CLSI) except for ampicillin (82.7% Italy, 81.1% Spain) and trimethoprim/sulfamethoxazole (71.1% Italy, 68.0% Spain). Susceptibility by EUCAST was similar to CLSI, except for cefuroxime (82.3% Italy, 87.3% Spain susceptible, increased exposure versus 100% by CLSI). Conclusions: Susceptibility of S. pneumoniae to many antibiotics was low in both countries, with susceptibility > 90% observed only with high-dose penicillin and fluoroquinolones (CLSI and EUCAST) and high-dose amoxicillin or amoxicillin/clavulanic acid (PK/PD). Higher susceptibility was seen with H. influenzae in both countries. Continued surveillance of antimicrobial resistance is important for guiding therapy of CA-RTIs.