Rapid Blood Culture Growth Signals Higher Mortality Risk in ICU Bacteremia

Critically ill patients whose blood cultures turn positive within six hours of collection showed a higher rate of death in hospital than those whose cultures flagged later, although the difference did not reach statistical significance, according to a retrospective cohort study published in BMC Infectious Diseases on 27 August 2026. The analysis drew on intensive care unit patients treated across the AdventHealth Central Florida Division hospital system between July 1, 2023, and June 30, 2025. Researchers Nicole Rios Serrano, Lena Kim Tran, and Christopher David Lloyd evaluated whether a shorter time to positivity, the interval before an incubating blood culture signals bacterial growth, was associated with increased in-hospital mortality among adults with bacteremia.

The study included 166 ICU patients with positive blood cultures in its final analysis. The team divided them into two groups: 81 patients whose initial cultures turned positive in under 360 minutes, described as rapid time to positivity, and 85 patients whose cultures took longer than 360 minutes, described as prolonged time to positivity. The primary outcome was in-hospital mortality.

Secondary outcomes included the time to empiric antimicrobial therapy, the time to a positive blood culture, whether empiric antibiotics appropriately covered the pathogen, the length of definitive treatment, and the overall hospital length of stay. The central result was a numerical gap that fell short of statistical significance. Patients in the rapid time-to-positivity group experienced all-cause in-hospital mortality of 47 percent, compared with 39 percent in the prolonged group, yielding a p-value of 0.292.

The observed eight-percentage-point excess in deaths among patients with faster-growing cultures was not large enough, in a sample of this size, to rule out chance as an explanation. The authors nonetheless interpret the direction of the association as consistent with the hypothesis that rapid microbial growth may reflect a higher burden of infection. The multivariable analysis sharpened the picture of what was associated with mortality in this cohort.

Conversely, consultation with an infectious disease specialist was independently associated with reduced mortality. These adjusted associations suggest that the virulence of the organism, the patient's baseline physiological state, and access to specialist expertise shaped outcomes in this cohort more clearly than the raw speed of culture growth itself. One of the study's notable findings concerns what rapid time to positivity did not change.

Although fast-growing cultures might be expected to accelerate clinical decision-making, the researchers found that a shorter time to positivity did not shorten the time to empiric or definitive antimicrobial therapy. In this cohort, clinicians were not starting antibiotics any sooner for patients whose cultures flagged quickly, which means any survival disadvantage carried by those patients was not offset by faster treatment initiation. The authors state that these findings support existing evidence that shorter time to positivity may serve as an early surrogate marker of bacterial burden and illness severity in critically ill patients with bacteremia.

Because rapid growth in the laboratory did not translate into faster antimicrobial therapy in this study, the association with higher mortality, if real, would point to the speed of culture positivity as a signal of how heavily infected a patient already is, rather than as a trigger that changed treatment timing in the hospitals examined. The study's design imposes important limits on how far its conclusions can be pushed. As a retrospective analysis of a single hospital system with a modest sample size, it can identify associations but cannot prove that rapid culture growth causes worse outcomes, and the non-significant mortality difference leaves genuine uncertainty about the strength of the relationship.

The findings should therefore be read as observational rather than practice-changing. Even so, the study contributes a concrete observation to the management of bacteremia in the ICU. By documenting that the mortality pattern held in a contemporary cohort of critically ill patients, and by highlighting MRSA bacteremia, higher APACHE II scores, and infectious disease consultation as the factors most tightly tied to survival in the adjusted analysis, the study offers ICU teams a candidate early marker alongside established severity measures.

Subject of Research: Impact of time to positive blood culture on mortality in intensive care unit patients with bacteremia: a retrospective cohort study

Article Title: Impact of time to positive blood culture on mortality in intensive care unit patients with bacteremia: a retrospective cohort study

Article References: Rios Serrano, N., Tran, L. K., & Lloyd, C. D. (2026). Impact of time to positive blood culture on mortality in intensive care unit patients with bacteremia: a retrospective cohort study. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14299-y

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14299-y

Keywords: Impact, time, positive, blood, culture, mortality, intensive, care, unit, patients, bacteremia, retrospective