Heterogeneity In Staphylococcus aureus Bacteraemia Clinical Trials Complicates Interpretation Of Findings

Clinical Subphenotypes of Staphylococcus aureus Bacteremia

BACKGROUND

Staphylococcus aureus bacteremia (SAB) is a clinically heterogeneous disease. The ability to identify subgroups of patients with shared traits (subphenotypes) is an unmet need to allow patient stratification for clinical management and research. We aimed to test the hypothesis that clinically relevant subphenotypes can be reproducibly identified among patients with SAB.

METHODS

We studied 3 cohorts of adults with monomicrobial SAB: a UK retrospective observational study (Edinburgh cohort, n = 458), the UK ARREST trial (n = 758), and the Spanish SAFO trial (n = 214). Latent class analysis was used to identify subphenotypes using routinely collected clinical data without considering outcomes. Mortality and microbiologic outcomes were then compared between subphenotypes.

RESULTS

Included patients had predominantly methicillin-susceptible SAB (1366 of 1430, 95.5%). We identified 5 distinct, reproducible clinical subphenotypes: (A) SAB associated with older age and comorbidity, (B) nosocomial intravenous catheter-associated SAB in younger people without comorbidity, (C) community-acquired metastatic SAB, (D) SAB associated with chronic kidney disease, and (E) SAB associated with injection drug use. Survival and microbiologic outcomes differed between the subphenotypes. Mortality was highest in subphenotype A and lowest in subphenotypes B and E. Microbiologic outcomes were worse in subphenotype C. In a secondary analysis of the ARREST trial, adjunctive rifampicin was associated with increased mortality in subphenotype B and improved microbiologic outcomes in subphenotype C.

CONCLUSIONS

We have identified reproducible and clinically relevant subphenotypes within SAB and provide proof of principle of differential treatment effects. Through clinical trial enrichment and patient stratification, these subphenotypes could contribute to a personalized medicine approach to SAB.

Distinct Clinical Endpoints of Staphylococcus aureus Bacteraemia Complicate Assessment of Outcome

BACKGROUND

We aimed to test the hypothesis that development of metastatic infection represents a distinct clinical endpoint from death due to Staphylococcus aureus bacteremia (SAB).

METHODS

We conducted a retrospective observational study of adults with SAB between 20 December 2019 and 23 August st2022 (n = 464). Simple logistic regression, odds ratios, and z-scores were used to compare host, clinical, and microbiologic features.

RESULTS

Co-occurrence of attributable mortality and metastatic infection was infrequent. Charlson Comorbidity Index and age were strongly associated with attributable mortality, but not metastatic infection. We compared patients with fatal SAB (without clinically-apparent metastatic complications, 14.4% of cohort), metastatic SAB (without attributable mortality, 22.2%), neither complication (56.7%), and overlapping fatal/metastatic SAB (6.7%). Compared to SAB without complications, fatal SAB was specifically associated with older age and multi-morbidity. Metastatic SAB was specifically associated with community acquisition, persistent fever, persistent bacteremia, and recurrence. Endocarditis was over-represented in the fatal/metastatic SAB overlap group, which shared patient characteristics with fatal SAB. In contrast to other (predominantly musculoskeletal) metastatic complications, endocarditis was associated with increased mortality, with death occurring in older multi-morbid patients later after SAB onset.

CONCLUSIONS

Patients with SAB experience distinct clinical endpoints: (i) early death, associated with multi-morbidity and age; (ii) metastatic (predominantly musculoskeletal) SAB; (iii) endocarditis, associated with late death occurring in older people with multi-morbidity, and (iv) bacteraemia without complications. These distinctions could be important for selecting appropriate outcomes in clinical trials: different interventions might be required to reduce mortality versus improve clinical response in patients with metastatic SAB.

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.

Which trial do we need? Next-generation sequencing to individualize therapy in Staphylococcus aureus bacteraemia

We propose a two-stage clinical trial in patients with Staphylococcus aureus bacteremia (SAB). In Stage 1 we will evaluate metagenomic next generation sequencing from blood as a quantitative biological surrogate for clinical endpoint in patients with SAB, similar to quantitative HIV viral load in HIV-infected patients. In Stage 2, we will conduct a randomized controlled trial to individualize duration of antibiotic therapy for based upon the presence of S. aureus genetic material in patients’ blood. The proposed study addresses two critical aspects of treatment of patients with SAB: the identification of a surrogate biological endpoint for future clinical trials, and a new approach by which to individualize patient management.