INTRODUCTION
Annually, nearly 2 million episodes of bloodstream infections (BSI) occur in North America and Europe, leading to around 250,000 deaths (
1), and BSI is the 11th most common cause of death in the United States (
2). BSI caused by Gram-negative bacteria account for approximately 45% of all cases of community-acquired and almost one-third of all health care-associated cases of bacteremia, with
Escherichia coli being the most prevalent Gram-negative pathogen for both types of bacteremia (
3). Timely administration of the appropriate antibiotic treatment remains the cornerstone for favorable clinical outcome in patients with BSI (
4–6).
Determining the appropriate duration of therapy is included in the CDC Strategic Priorities for Combating Antimicrobial Resistance (
7) and is part of the National Action Plan for Combating Antibiotic-Resistant Bacteria (
8). However, the optimal duration of antibiotic therapy has yet to be defined. The current Infectious Diseases Society of America guidelines suggest that the duration of treatment for intravascular catheter-related Gram-negative bacteremia should be between 7 and 14 days (
9), but there is no consensus on the optimal duration of the antimicrobial therapy for non-catheter-related Gram-negative bacteremia. Recently published studies on non-catheter-related bacteremia due to
Enterobacteriaceae compared the outcomes of short (≤10 days) with longer (>10 days) treatment in terms of clinical outcomes in an attempt to define the optimal duration of therapy, but their findings are controversial (
10,
11). The aim of the present study is to evaluate short versus longer courses of antibiotic treatment for bacteremia due to
Enterobacteriaceae in clinical outcomes.
DISCUSSION
Prolonged courses of antibiotics have been associated with increased adverse events (
26) and the emergence of antibiotic-resistant strains (
27–29), while inadequate courses lead to ineffective treatment and relapse of the infection (
30). In this meta-analysis, we evaluated short versus longer courses of antibiotic for the treatment of bacteremia due to
Enterobacteriaceae in terms of all-cause mortality, clinical cure, and relapse of bacteremia. We found that shorter courses of antibiotics (≤10 days) did not result in inferior clinical outcomes compared to longer courses of treatment. Notably, the included studies did not differ in terms of patient population and source of bacteremia and patient characteristics between the compared treatment groups. The lack of statistical heterogeneity from all analyses further strengthens these findings.
There is a scarcity of evidence regarding the optimal duration of antibiotic therapy for non-catheter-related Gram-negative bacteremia, and the limited studies that exist present controversial findings (
10,
11). As a result, there is wide variation in treatment duration among clinicians, with a general tendency toward more prolonged courses (
31). For example, according to a survey among infectious diseases and critical care physicians, the most common response was 14 days of treatment for BSI, irrespective of its source. However, in terms of duration of treatment, the majority of respondents recommended treatment for 7 to 10 days for all bacteremic syndromes, such as bacteremic urinary tract infection and bacteremic pneumonia (
31). On the contrary, herein, we found that antibiotic treatment for 10 days or less for bacteremia due to
Enterobacteriaceae was not associated with improved outcomes and cannot replace yet the standard of care with treatment for over 10 days.
The impact of treatment duration on antimicrobial resistance is another factor taken into account in the selection of the treatment regimen. Emergence of multidrug resistance during therapy was evaluated in one of the included studies, in which 4.4% versus 7.3% cases of multidrug-resistant bacteria occurred in the short- and long-course groups, respectively, without a significant difference between the compared arms (
10). Likewise, no significant difference in the emergence of resistance was found between short- and long-course groups in the randomized controlled trial (10.8% versus 9.8%, respectively;
P = NS) (
19). On the other hand, antibiotic use is associated with
Clostridioides (
Clostridium)
difficile infection (CDI) (
32). Two of the included studies assessed the development of CDI between the short- and long-course groups, and both studies found that there was no significant difference between the compared treatments (
10,
19).
Moreover, appropriateness of empirical therapy is another important factor that affects treatment outcome and should be assessed as a potential confounder in the results of the included studies (
33). Two studies provided information on the empirical therapy, with one showing no difference in the occurrence of inappropriate empirical therapy between short- and long-course treatments (
11) and the other showing more common inappropriate therapy in the short-course group (
20). Besides the difference in the appropriateness of therapy noted in the latter study, clinical cure, relapse, and mortality did not differ significantly between short- and long-course treatments (
20).
The present study bears certain limitations that should be considered in the interpretation of the findings. First, all but 1 included study were retrospective cohort, meaning that the quality of the data may be suboptimal or the data are prone to confounding factors. To eliminate confounding by indication, the authors of 1 study excluded patients in whom antimicrobial duration of treatment was dictated by outcome (in-hospital mortality) or clinical response to therapy (prolonged hospitalization) (
11). In order to address this issue, another study included propensity score matching (
10), while a third study utilized a propensity score of receiving short-course treatment using multivariate logistic regression (
20). The randomized controlled trial did not bear confounding by indication due to randomization. However, it should be noted that the authors excluded hemodynamically unstable patients who tend to receive antibiotic treatment for longer periods (
19). Moreover, in nonrandomized studies, survival bias might occur (
34). In 3 out of 4 nonrandomized studies that were included in our meta-analysis, the authors addressed this concern. More specifically, in 1 study, the authors mentioned that in order to reduce the risk of survival bias, they excluded patients who did not survive initial hospitalization for bloodstream infection (
11). Also, in 2 other studies, the authors excluded from the analyses all patients who died while receiving antibiotic treatment for bloodstream infection (
10,
20). Second, mortality was assessed at either 30 days (
10) or 90 days (
11,
19,
20). Given that bacteremia is associated with long-term mortality (
35), assessment of the effectiveness of the definitive treatment at 90 rather than 30 days may be preferable. In addition, clinical outcomes (such as the source or severity of bacteremia, the presence of comorbidities, and the antimicrobial resistance profile of the involved pathogens) were not available, and clearer conclusions could not be drawn. Third, the impact of treatment duration on outcomes may depend on the type of antibiotic used; however, data on the specific antibiotics used were not provided in the included studies. Interestingly, according to a previously published study which assessed the effectiveness of oral antibiotics in the treatment of Gram-negative bacteremia, clinical outcomes improve with oral antibiotics of high bioavailability compared to outcomes with antibiotics of moderate or low bioavailability (such as cephalosporins or penicillins) (
36).
In conclusion, in patients with bacteremia due to
Enterobacteriaceae, treatment for ≤10 days did not result in inferior clinical outcomes compared to treatment for >10 days. The current practice for the treatment of Gram-negative bacteremia varies widely (
31). Further well-designed studies that will compare effectiveness, safety, and the emergence of resistance between short- and long-course treatments are necessary in order to assess whether shortening of treatment duration in specific sources of bacteremia would be beneficial. Also, future studies that include patients with bacteremia of urinary source should investigate whether clinical outcomes with short- versus long-course treatment differ based on sex. Last, cost-effectiveness analyses should be performed to evaluate whether differences in the duration of antibiotic treatment for bacteremia impact health care cost.
MATERIALS AND METHODS
Literature search.
We performed a systematic search of the available literature in the PubMed and EMBASE databases through May 2018. The following search terms were applied: “(“bloodstream infection” OR bacteremia OR sepsis OR septicemia) AND treatment AND (short-course OR long-course OR prolonged) AND (cure OR failure OR mortality).” A year limit to 1990 was set, and all articles published in English, German, or French were evaluated.
Study selection.
We defined short-course treatment as treatment for ≤10 days and long-course treatment as treatment for >10 days. As such, studies comparing the clinical outcomes between patients who received antibiotic treatment for ≤10 days and those who received treatment for >10 days were considered eligible for inclusion. Studies assessing clinical outcomes between different treatment duration groups using a cutoff other than 10 days were evaluated and discussed but were not included in the meta-analysis. Studies reporting only the mean or median data without a minimum duration of therapy were not eligible for inclusion. Also, studies reporting on antibiotics that are not currently approved by the Food and Drug Administration were excluded. Last, case reports and studies including pediatric patients were also excluded.
Data extraction and quality assessment.
Two investigators (G.S.T. and N.A.) independently performed the systematic search of databases, study selection, and data extraction. Any discrepancies between the investigators were resolved by consensus during meetings. The extracted data included the main characteristics of each study (first author name, year, and study design), number of patients with bacteremia who received antibiotic treatment, source of bacteremia, causative pathogen of bacteremia, aggregate Newcastle-Ottawa scale score, duration of antibiotic therapy in both arms, as well as the available clinical outcomes in each treatment group.
The methodological quality of the nonrandomized studies that were included in the meta-analysis was assessed with the “star system” of the Newcastle-Ottawa scale (
37). The studies were evaluated according to the selection of study groups, comparability of groups, and ascertainment of the outcome of interest.
Definitions and outcomes.
The primary outcome of the meta-analysis was all-cause mortality. Clinical cure, as defined by the investigators of the individual studies, and relapse of bacteremia were the secondary outcomes.
Meta-analysis.
The meta-analysis was performed using Review Manager for Windows, version 5.3 (
38). Pooled risk ratios and 95% confidence intervals were calculated regarding the outcomes of interest. We assessed statistical heterogeneity among studies by using a χ
2 test (
P < 0.10 was defined to indicate significant heterogeneity) and
I2. When there was no significant statistical heterogeneity (<40%) (
39) between the studies, the Mantel-Haenszel fixed-effect model was used (
40). Otherwise, the random-effects model with the DerSimonian and Laird approach was used as appropriate (
41). We assessed publication bias using a funnel plot (
41).