Differences in isolation rate and antimicrobial susceptibility of bacteria isolated from foals with sepsis at admission and after ≥48 hours of hospitalization

BACKGROUND: Antimicrobial treatment protocols for foals with sepsis that do not improve clinically often are adjusted based on bacteriological and antimicrobial susceptibility testing results from samples collected at hospital admission. OBJECTIVES: To evaluate whether hospitalization for ≥48 hours affects bacteriological and antimicrobial susceptibility testing results. ANIMALS: Two‐hundred sixty‐seven foals <30 days of age admitted to a neonatal intensive care unit and diagnosed with sepsis. METHODS: Medical records were reviewed retrospectively to identify foals with sepsis and positive bacteriological cultures. Results from samples collected at hospital admission were compared to those collected ≥48 hours after admission. Logistic regression for clustered data and exact logistic regression were used for statistical analysis. RESULTS: Three‐hundred fifty‐three unique bacterial isolates were obtained from 231 foals at hospital admission and 92 unique bacterial isolates were obtained from 57 foals after ≥48 hours of hospitalization. Relative isolation frequency after ≥48 hours of hospitalization increased for Acinetobacter spp., 0.6% versus 3.3% (odds ratio [OR], 7.63; 95% confidence interval [CI], 1.28‐45.45); Enterococcus spp., 4.8% versus 19.6% (OR, 5.37; 95% CI, 2.64‐10.90); Klebsiella spp., 5.1% versus 10.9% (OR, 2.27; 95% CI, 1.05‐4.89); Pseudomonas spp., 3.0% versus 7.6% (OR, 3.49; 95% CI, 3.49‐240.50); and Serratia spp., 3.0% versus 5.4% (OR, 20.23; 95% CI, 2.20‐186.14). Bacteria isolated after ≥48 hours of hospitalization were less susceptible to all tested antimicrobial drugs, except for imipenem. CONCLUSIONS AND CLINICAL IMPORTANCE: Decreased antimicrobial susceptibility of bacteria isolated after ≥48 hours of hospitalization provides a rationale for repeated bacteriological culture and susceptibility testing in hospitalized foals with sepsis.