Shifting epidemiology of bloodstream infections during the pandemic era: a comparative analysis of blood cultures from adult intensive care unit patients

The COVID-19 pandemic required substantial reorganization of hospital services, with potential implications for infection prevention, blood culture quality, and bloodstream infection epidemiology. This study compared blood culture outcomes before the pandemic and among adult intensive care patients with and without COVID-19 during the pandemic. This retrospective, single-center observational study included blood culture sets obtained from adult intensive care unit patients between January 2017 and May 2021. Sets were classified as pre-pandemic, COVID-19, or non-COVID pandemic. Blood culture contamination, clinically true growth, polymicrobial bloodstream infection, microorganism distribution, and selected resistance markers were compared using the chi-square test or Fisher’s exact test, with Bonferroni adjustment for pairwise comparisons. Proportion ratios with 95% confidence intervals were calculated. Among 3,692 blood culture sets, 1,638 were pre-pandemic, 1,088 were from patients with COVID-19, and 966 were from patients without COVID-19 during the pandemic. Contamination differed among all groups and was highest in the COVID-19 group, followed by the non-COVID pandemic and pre-pandemic groups (17.4%, 12.4%, and 6.3%; p < 0.001). Clinically true growth (31.9% vs. 22.9% and 16.1%) and polymicrobial bloodstream infection (7.6% vs. 3.6% and 3.1%) were more frequent in the COVID-19 group than in the non-COVID pandemic and pre-pandemic groups (both p < 0.001). Acinetobacter baumannii was most frequent in the COVID-19 group (12.2%), followed by the non-COVID pandemic (3.8%) and pre-pandemic groups (2.2%), with significant differences in all pairwise comparisons. It was 5.56-fold more frequent in the COVID-19 than in the pre-pandemic group (95% confidence interval, 3.88–7.97). Klebsiella pneumoniae was more frequent in both pandemic groups. Staphylococcus aureus , coagulase-negative staphylococci, and Stenotrophomonas maltophilia were more frequent in the COVID-19 group than in the pre-pandemic group. No significant differences were detected in the proportions of methicillin-resistant Staphylococcus aureus or vancomycin-resistant enterococci, or in the frequency of Candida species. The pandemic was associated with changes in blood culture outcomes, including higher proportions of contamination, clinically true growth, and polymicrobial bloodstream infection, particularly among patients with COVID-19. These findings highlight the importance of monitoring blood culture contamination during healthcare crises. Further patient-level studies are needed to clarify the underlying factors.