Follow-up Blood Cultures in Gram-negative Bacteremia: How Do They Impact Outcomes?

Introduction: Several studies have questioned the utility of obtaining follow-up blood cultures in Gram-negative bacteremia, but the impact of this practice on clinical outcomes is not fully understood.

Methods: A retrospective cohort study of adult patients admitted with Gram-negative bacteremia over a two year period, to compare outcomes in those with and without follow-up blood cultures obtained. Data collected included demographics, comorbidities and presumed source of bacteremia. White blood cell count and presence of fever or hemodynamic compromise on the day of follow-up blood culture were recorded. The primary objective was to compare 30-day mortality between the two groups. Secondary objectives included comparing 30-day readmission rate, hospital length of stay and antibiotics duration.

Results: Of 482 included patients, 321 (66.6%) had follow-up blood cultures. 96% of follow-up blood cultures were negative. Persistent bacteremia occurred in 9 patients. There was no significant difference in 30-day mortality between those with and without follow-up blood cultures (2.9% and 2.7% respectively, > 0.999), and no difference in 30-day readmission rate (21.4% and 23.4% respectively, = 0.704). Patients with follow-up blood cultures had longer hospital length of stay (7 days vs 5 days, < 0.001), and longer mean antibiotic duration (14 days vs 11 days, < 0.001).

Conclusion: Obtaining follow-up blood cultures in Gram-negative bacteremia had no impact on 30-day mortality or 30-day readmission rates. It was associated with longer length of stay and antibiotic duration. We found this practice to be low yield and its routine use may be of questionable value.