Finetuning Antibiograms: A 25-year Experience

There remains debate whether antibiograms are essential for antibiotic stewardship.

First, to present the main organisms isolated from blood cultures from 2.5 decades (2000-2024) in 5-year periods and their susceptibility profiles. Second, to show the relevance of periodically updated antibiograms, stratified by major determinants of resistance.

A retrospective analysis of 733,714 blood cultures.

Data analysis of accrued blood culture results.

The true-positive (TP) rate/1000 admission days increased from 6.8 in the first 5-year period (2000-2004) to 13.5 in the last 5-year period (2020-2024, IRR ±95% CI, 1.206 [1.109-1.312], p=0.006). A total of 42,023 TP organisms were isolated from patients ≤72 hours in hospital and 27,952 from patients >72 hours in hospital. The rate of community-acquired Enterobacterales-producing-extended spectrum beta-lactamases (ESBL) increased from 26% to 32% over the study period, driving the decreasing susceptibility rates of cephalosporins (OR 1.08 [1.06-1.1]), p<0.001). Otherwise, no major changes in susceptibility rates were detected. The rates of methicillin susceptibility in S. aureus isolates only decreased in pediatric patients, from 93% in 2000-2004 to 79% in 2020-2024 (OR 0.78 [0.69-0.87], p<0.001), but improved for all other categories of patients (OR 1.09 [1.06-1.12], p<0.001).

Antibiograms depicting blood culture data from 5-year periods are very reliable because of the large number of included results. Major changes in susceptibilities were observed only for Enterobacterales' susceptibilities to cephalosporins because of increasing rates of ESBL. Stratification of susceptibilities by source of patients allows for design of protocols for empiric use of both community and hospital-acquired infections.