Duration of Therapy and Follow-up Blood Cultures in Bacteremia: New Information

Emily Spivak, MD, MHS


February 08, 2018

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Medscape &

Bloodstream Infections: Gaps in Knowledge

Gram-negative bacteremia accounts for up to half of all bloodstream infections, yet little is known about the shortest effective duration of therapy, and guideline recommendations do not exist outside of gram-negative catheter-related bloodstream infections, for which the recommendation is 7-14 days. Furthermore, the utility of follow-up blood cultures for gram-negative bloodstream infections is unclear yet may have implications for healthcare resource utilization and antibiotic use. Two recent studies[1,2] addressed these issues.

Effect of Duration of Therapy

Chotiprasitsakul and colleagues[1] performed a retrospective cohort study at three medical centers comparing clinical outcomes of adults with Enterobacteriaceae bacteremia treated with a short course (6-10 days) versus a prolonged course (11-16 days) of antibiotic therapy. Propensity score matching was used to estimate the impact of duration of therapy on all-cause mortality within 30 days after the end of antibiotic therapy between 385 matched pairs. Secondary outcomes included recurrent bloodstream infections, Clostridium difficile infections (CDIs), and the emergence of multidrug-resistant gram-negative bacterial infection or colonization in the 30 days after the end of antibiotic therapy.

The median duration of therapy in the short-course and prolonged-course groups was 8 days (interquartile range [IQR], 7-9 days) and 15 days (IQR, 13-15 days), respectively. No difference in mortality was seen between groups (adjusted hazard ratio, 1.0; 95% confidence interval [CI], 0.62-1.63). Moreover, the odds of recurrent bloodstream infection and CDI were similar between groups, with a trend toward a protective effect of short-course therapy on the emergence of multidrug-resistant gram-negative bacteria (odds ratio, 0.59; 95% CI, 0.32-1.09; P = .09). Most patients had urinary, biliary, or gastrointestinal sources of bacteremia, and only 2.2% had inadequate source control.

Given similar clinical outcomes with short-course therapy as well as a potential protective effect against antibiotic-resistant organisms, this study has implications for antibiotic stewardship programs and supports efforts to shorten durations of therapy.

Frequency of Follow-up Blood Cultures

In the second study, Canzoneri and colleagues[2] retrospectively evaluated 500 episodes of bacteremia at a single center to determine the frequency with which follow-up blood cultures are obtained and the risk factors for persistent bacteremia, defined as positive blood cultures with the same original organism in a sample drawn at least 24 hours after the initial culture. At least one follow-up culture was obtained in 383 bacteremia episodes (77%). Patients with gram-positive bacteremias were more likely (54%) to undergo follow-up blood cultures than those with gram-negative bacteremias (37%). Of the 55 (14% of 383) positive follow-up blood cultures, 43 (78%) grew gram-positive cocci, and eight (15%) grew gram-negative bacilli. The presence of fever on the day of follow-up blood cultures was associated with culture positivity.

On the basis of this study, approximately five follow-up blood cultures are needed to yield one positive result for gram-positive organisms, as opposed to 17 follow-up blood cultures to yield one positive result for gram-negative organisms. The study authors concluded that follow-up blood cultures are likely of minimal value in the management of gram-negative bacteremia and may lead to prolonged lengths of stay, prolonged antibiotic courses, and higher healthcare costs.

Taken together, these studies highlight opportunities to streamline care for gram-negative bloodstream infections while improving antibiotic use and healthcare utilization.


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