How generalizable are randomized controlled trials (RCTs) in Staphylococcus aureus bacteremia? A description of the mortality gap between RCTs and observational studies

Are we enrolling the right patients? A scoping review of external validity and generalizability of clinical trials in bloodstream infections

BACKGROUND

Having a representative population in randomized clinical trials (RCTs) improves external validity and generalizability of trial results. There are limited data examining differences between RCT-enrolled and real-world populations in bloodstream infections (BSI).

OBJECTIVES

We conducted a scoping review aiming to review studies assessing generalizability of BSI RCT populations, to identify sub-groups that have been systematically under-represented and to explore approaches to improve external validity of future RCTs.

SOURCES

MEDLINE, Embase, and Cochrane Library databases were searched for terms related to external validity or generalizability, BSI, and clinical trials in papers published up to 1 August 2023. Studies comparing enrolled versus nonenrolled patients, or papers discussing external validity or generalizability in the context of BSI RCTs were included.

CONTENT

Sixteen papers were included in the final review. Five compared RCT-enrolled and nonenrolled participants from the same source population. There were significant differences between the two groups in all studies, with nonenrolled patients having a greater comorbidity burden and consistently worse outcomes including mortality. We identified several barriers to improving generalizability of RCT populations and outlined potential approaches to reduce these barriers, such as alternative/simplified consent processes, streamlining eligibility criteria and follow-up procedures, quota-based sampling techniques, and ensuring diversity in site and study team selection.

IMPLICATIONS

Study cohorts in BSI RCTs are not representative of the general BSI patient population. As we increasingly adopt large pragmatic trials in infectious diseases, it is important to recognize the importance of maximizing generalizability to ensure that our research findings are of direct relevance to our patients.

Observational versus randomized controlled trials to inform antibiotic treatment durations: a narrative review

BACKGROUND

Studies comparing shorter and longer antibiotic treatment durations are increasingly common. Randomized controlled trials (RCTs) are an ideal methodological approach to study antibiotic treatment durations; however, these trials can be logistically and financially challenging to conduct.

OBJECTIVES

In this narrative review, we sought to compare the strengths and limitations of observational study data with those of RCT data in evaluating antibiotic treatment durations. We used uncomplicated Gram-negative bacteraemia as an illustrative case example because several published RCTs and observational studies have been conducted in similar patient populations.

SOURCES

We searched MEDLINE for articles comparing treatment durations for gram-negative bacteremia from inception to June 9th, 2022. We included studies reporting on all-cause mortality and/or relapse at day 28-30. Data comparing short- versus long-course therapy were pooled by Bayesian random effects meta-analyses to assess the odds ratios (OR) of all-cause mortality and relapse at 30 days, stratified by study design. Parameters were summarized with median and 95% highest-density credible intervals (CrI). Posterior probabilities of OR > 1.0 were estimated. Observational studies were further examined to determine if and how they addressed potential sources of bias.

CONTENT

We identified 1671 unique records and included 10 studies (seven observational and three RCTs). With respect to 30-day mortality, the Bayesian posterior probability that a longer course of therapy was better (i.e. OR >1.0) was 42% in RCTs (OR, 0.94; 95% CrI, 0.51-1.68) and 91% in observational studies (OR, 1.25; 95% CrI, 0.88-1.73). No observational study fully addressed all potential sources of bias.

IMPLICATIONS

On the basis of our findings, we discuss future directions for antibiotic treatment duration trials, including approaches to limit sources of bias in observation data and novel trial designs.

Optimizing patient recruitment into clinical trials of antimicrobial-resistant pathogens

Recruitment of patients with critical priority antimicrobial-resistant (AMR) bacteria into drug approval randomized controlled trials (RCTs) has not been successful to date. Approaching from the viewpoint of clinician-investigators and learning from the experience of AMR-focused investigator-initiated trials, we present suggestions to improve feasibility and efficiency of RCTs evaluating patients with severe infections caused by carbapenem-resistant Gram-negative or other AMR bacteria. Considerations address the trials' eligibility criteria, whether the focus of the trial is pathogen- or syndrome-targeted, trials' case report forms and monitoring, informed consent strategies for the recruitment of extremely ill patients, team dedication and incentives to run the trial and alternative trial designs. Evidence on the effects of new drugs against the AMR that these drugs target is weak and needs to be improved through better industry-academic collaboration, taking advantage of the different strengths of industry-led and investigator-initiated research.

Staphylococcus aureus bacteremia mortality across country income groups: A secondary analysis of a systematic review

OBJECTIVES

Staphylococcus aureus bacteremia (SAB) is a common infection worldwide. We compared SAB mortality in low- and middle-income countries (LMIC) versus high-income countries (HIC) in a meta-analysis.

METHODS

We searched MEDLINE, Embase, and Cochrane Database of Systematic Reviews from 1991-2021 and included observational, single-country studies on patients with positive blood cultures for S. aureus. The main outcome was the proportion of patients with SAB who died in the hospital. A generalized linear mixed random-effects model was used to pool estimates, and a meta-regression was used to adjust for study-level characteristics.

RESULTS

A total of 332 studies involving 517,671 patients in 39 countries were included. No study was conducted in a low-income country. Only 33 (10%) studies were performed in middle-income countries (MIC), which described 6,216 patients. The pooled in-hospital mortality was 32.4% (95% confidence interval [CI] 27.2%-38.2%, T2 = 0.3063) in MIC and 22.3% (95% CI 20.1%-24.6%, T2 = 0.3257) in HIC. In a meta-regression model, MIC had higher in-hospital mortality (adjusted odds ratio 1.37, 95% CI 1.11-1.71; P = 0.0042) than HIC.

CONCLUSION

In SAB studies, LMIC are poorly represented. In-hospital mortality was significantly higher in MIC than in HIC. Research should be conducted in LMIC to characterize differences in care processes driving the mortality gap.

Heterogeneity In Staphylococcus aureus Bacteraemia Clinical Trials Complicates Interpretation Of Findings

We systematically evaluated randomized-controlled trials (RCTs) for Staphylococcus aureus bacteremia (SAB). There was intertrial heterogeneity in cohort characteristics, including bacteremia source, complicated SAB, and comorbidities. Reporting of cohort characteristics was itself variable, including bacteremia source and illness severity. Selection bias was introduced by exclusion criteria relating to comorbidities, illness severity, infection types, and source control. Mortality was lower in RCT control arms compared with observational cohorts. Differences in outcome definitions impedes meta-analysis. These issues complicate the interpretation and application of SAB RCT results. The value of these trials should be maximized by a standardized approach to recruitment, definitions, and reporting.

Staphylococcus aureus bacteremia mortality: A systematic review and meta-analysis

BACKGROUND

Precise estimates of mortality in Staphylococcus aureus bacteremia (SAB) are important to convey prognosis and guide design of interventional studies.

OBJECTIVE

We performed a systematic review and meta-analysis to estimate the all-cause mortality in SAB and to explore how it changed with time.

DATA SOURCES

MEDLINE, Embase, and Cochrane Database of Systematic Reviews from January 1, 1991 to May 7, 2021.

STUDY ELIGIBILITY CRITERIA

Human observational studies on patients with S. aureus bloodstream infection.

PARTICIPANTS

Patients with a positive blood culture for S. aureus.

METHODS

Two independent reviewers extracted study data and assessed risk of bias using the Newcastle Ottawa Scale. A generalized linear mixed random effects model was used to pool estimates.

RESULTS

A total of 341 studies were included, which described 536,791 patients. From 2011 onwards, the estimated mortality was 10.4% (95% confidence interval (CI) 9.0%-12.1%) at 7 days, 13.3% (95% CI 11.1%-15.8%) at 2 weeks, 18.1% (95% CI 16.3%-20.0%) at 1 month, 27.0% (95% CI 21.5%-33.3%) at 3 months, and 30.2% (95% CI 22.4%-39.3%) at 1 year. In a meta-regression model of 1-month mortality, methicillin-resistant S. aureus (MRSA) had a higher mortality (adjusted odds ratio (aOR) 1.04 95% CI 1.02-1.06 per 10% increase in MRSA proportion), and compared to prior to 2001, more recent time periods had lower mortality (aORs 0.88 [95% CI 0.75-1.03] for 2001 to 2010; 0.82 [95% CI 0.69-0.97] for 2011 onwards).

CONCLUSIONS

SAB mortality has decreased over the last 3 decades. However, more than 1 in 4 patients will die within 3 months and continuous improvement in care remains necessary.

REGISTRATION

PROSPERO CRD42021253891.