Changes in antimicrobial resistance of staphylococci isolated from bloodstream infection and the impact of COVID-19.

OBJECTIVE

To analyze the changes in antimicrobial resistance of Staphylococcus aureus (S. aureus) and coagulase-negative staphylococci (CoNS) in bloodstream infections (BSIs) between 2018 and 2024, and to assess temporal associations with the COVID-19 pandemic.

METHODS

A total of 575 S. aureus and 1,014 CoNS isolates from blood cultures were retrospectively reviewed. To define true CoNS BSI, we applied clinical criteria (≥ 2 positive bottles with same species, or 1 positive bottle with clinical signs + central line + targeted therapy). Demographic characteristics and resistance rates to 15 antimicrobial agents were compared using chi-square (χ2) and Mann-Kendall tests, with 95% confidence intervals (CIs) and Bonferroni correction for multiple comparisons.

RESULTS

CoNS infections were more common in minors (0-17 years: 31.3%) and the elderly (≥ 80 years: 13.7%), while S. aureus predominated in adults 18-65 years (51.8%). CoNS exhibited higher resistance rates than S. aureus to oxacillin (75.2% vs. 30.5%, p < 0.001), ciprofloxacin (42.8% vs. 17.5%, p < 0.001) and erythromycin (82.2% vs. 56.1%, p < 0.001). Methicillin-resistant CoNS (MRCNS) detection rates exceeding 70% throughout. Penicillin G resistance in S. aureus increased from 87.1% (95% CI 78.0-93.0) in 2018 to 100% (95% CI 92.5-100) in 2024 (nominal P < 0.05, but not significant after correction). Following the pandemic onset, resistance rates to penicillin G, clindamycin, and ciprofloxacin further increased in both groups. After Bonferroni correction, the pandemic-period resistance rate increases of penicillin G, oxacillin, clindamycin, and erythromycin for S. aureus remained significant, while those for CoNS did not. No resistance to linezolid, vancomycin, or tigecycline was detected.

CONCLUSION

Staphylococci resistance in blood isolates has intensified, with temporal associations observed during the Coronavirus Disease 2019 (COVID-19) pandemic. Clinicians should reconsider empirical oxacillin use given persistently high methicillin resistance. Ongoing surveillance and antimicrobial stewardship are essential. Causal attribution is not possible due to uncontrolled confounders.