COVID-19 intensive care patients had more contaminated and polymicrobial blood cultures

Blood cultures collected from adult intensive care unit patients with COVID-19 had higher rates of contamination, clinically true microbial growth and polymicrobial bloodstream infection than cultures collected before the pandemic or from patients without COVID-19 during the pandemic. A retrospective, single-center observational study analyzed 3,692 blood culture sets obtained between January 2017 and May 2021: 1,638 from the pre-pandemic period, 1,088 from patients with COVID-19 and 966 from patients without COVID-19 during the pandemic. Contamination was most frequent in the COVID-19 group, at 17.4%, compared with 12.4% in the non-COVID pandemic group and 6.3% before the pandemic.

The overall difference was statistically significant, with p<0.001. Clinically true growth was also more frequent among patients with COVID-19. It occurred in 31.9% of COVID-19 culture sets, compared with 22.9% of sets from patients without COVID-19 during the pandemic and 16.1% of pre-pandemic sets.

Both comparisons produced p-values below 0.001. These percentages describe outcomes among the culture sets collected; they do not directly estimate an individual patient’s probability of developing a bloodstream infection. The distribution of individual microorganisms also differed across the three groups.

Acinetobacter baumannii was the most frequently detected organism among patients with COVID-19, appearing in 12.2% of culture sets, compared with 3.8% in the non-COVID pandemic group and 2.2% in the pre-pandemic group. All pairwise comparisons were statistically significant. The proportion ratio for A. baumannii in the COVID-19 group relative to the pre-pandemic group was 5.56, with a 95% confidence interval of 3.88–7.97.

Klebsiella pneumoniae was more frequent in both pandemic groups than before the pandemic. Staphylococcus aureus , coagulase-negative staphylococci and Stenotrophomonas maltophilia were also more frequent in the COVID-19 group than in the pre-pandemic group, although the supplied findings do not report the corresponding proportion ratios or confidence intervals for each of those organisms. Not every microbiological measure changed in parallel with the overall pattern.

The researchers detected no significant differences in the proportions of methicillin-resistant Staphylococcus aureus or vancomycin-resistant enterococci, and they found no significant difference in the frequency of Candida species. Comparisons were performed using the chi-square test or Fisher’s exact test, with Bonferroni adjustment for pairwise comparisons, and proportion ratios were calculated with 95% confidence intervals. The retrospective design and single-center scope limit the conclusions that can be drawn.

The analysis identifies associations between group membership, pandemic period and blood-culture outcomes but does not establish that COVID-19 caused the observed changes. The investigators noted that the COVID-19 pandemic required substantial reorganization of hospital services, with potential implications for infection prevention and blood-culture quality. They identified monitoring of blood-culture contamination during healthcare crises as an important implication of the findings and said that further patient-level studies are needed to clarify the underlying factors.

Overall, the study documents a distinct blood-culture profile among adult intensive care patients with COVID-19: more contaminated sets, more sets with clinically true growth, more polymicrobial infections and a particularly high frequency of A. baumannii , while the measured resistance markers and Candida frequency did not differ significantly across the groups.

Subject of Research: Blood-culture epidemiology in adult intensive care patients during the COVID-19 pandemic

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

Article References: Yıldız Kaya, S., Kaya, A., Kurt, A. F., Çelik, Ö. F., Houssein, F. M., Kayhan, O., Bozbay, S., Karaali, R., Balkan, İ. İ., Mete, B., Saltoğlu, N., Tabak, F., & Aygün, G. (2026). Shifting epidemiology of bloodstream infections during the pandemic era: a comparative analysis of blood cultures from adult intensive care unit patients. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14680-x

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14680-x

Keywords: COVID-19, blood cultures, bloodstream infections, intensive care, culture contamination, polymicrobial infection, Acinetobacter baumannii, Klebsiella pneumoniae, antimicrobial resistance, pandemic epidemiology, Shifting, epidemiology