TOPLINE:

Critically ill patients with polymicrobial bloodstream infections had comparable 90-day all-cause mortality to those with monomicrobial infections, irrespective of whether potential contaminants were excluded. Other clinical and microbiological outcomes remained similar between groups.

METHODOLOGY:

• Investigators in Austria conducted a retrospective cohort study using medical records data to evaluate the impact of polymicrobial bloodstream infections on clinical outcomes in 3197 patients (median age, 61 years; 35.8% women) admitted to the ICU of a tertiary care hospital.
• This study analysed patients who were hospitalised for at least 3 days and had at least one positive blood culture; those with polymicrobial infections (n = 549) — defined as two or more distinct bacterial pathogens in a single blood culture — were compared to those with monomicrobial infections (n = 2648) who had a single bacterial pathogen.
• The primary outcome was 90-day all-cause mortality, and secondary outcomes included 30-day all-cause mortality, microbiological failure, the onset of fever, the development of acute respiratory distress syndrome, and the length of ICU and hospital stay.
• A secondary analysis was conducted in 1669 patients, excluding common commensal organisms to reduce the potential misclassification due to skin flora contamination.

TAKEAWAY:

• The risk for 90-day all-cause mortality did not differ significantly between polymicrobial and monomicrobial groups (adjusted risk difference, 2.84 percentage points; 95% CI, -1.19 to 6.88).
• Secondary outcomes — 30-day all-cause mortality, microbiological failure, the onset of fever, and the development of acute respiratory distress syndrome — did not differ significantly between the groups; the length of ICU and hospital stay was comparable.
• The analysis excluding common commensal organisms likewise showed no significant differences between the groups.

IN PRACTICE:

"Our findings add to the growing body of evidence suggesting that the presence of multiple bloodstream pathogens is not an independent driver of mortality in the ICU," the investigators reported.

"Consequently, in contemporary ICU settings with established treatment protocols and timely empiric broad-spectrum therapy, clinicians should not automatically anticipate poorer outcomes solely based on the detection of multiple pathogens," they added.

SOURCE:

This study was led by Anselm Jorda, Medical University of Vienna, Vienna, Austria. It was published online on September 24, 2025, in Open Forum Infectious Diseases.

LIMITATIONS:

Because the study was retrospective, residual confounding and bias cannot be ruled out. Although no major differences were observed in primary and secondary outcomes, the study may have been underpowered to detect small effects or rare complications. Results could not be stratified on the basis of infection source or pathogen type, and the findings from ICUs in tertiary care may not be generalisable to other healthcare settings.

DISCLOSURES:

This study received internal funding. The authors reported having no conflicts of interest relevant to this work.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.