Bias and Refinement of Multiscale Mean Field Models

Mean field approximation is a powerful technique which has been used in many settings to study large-scale stochastic systems. In the case of two-timescale systems, the approximation is obtained by a combination of scaling arguments and the use of the averaging principle. This paper analyzes the approximation error of this `average' mean field model for a two-timescale model $(\boldsymbol{X}, \boldsymbol{Y})$, where the slow component $\boldsymbol{X}$ describes a population of interacting particles which is fully coupled with a rapidly changing environment $\boldsymbol{Y}$. The model is parametrized by a scaling factor $N$, e.g. the population size, which as $N$ gets large decreases the jump size of the slow component in contrast to the unchanged dynamics of the fast component. We show that under relatively mild conditions the `average' mean field approximation has a bias of order $O(1/N)$ compared to $\mathbb{E}[\boldsymbol{X}]$. This holds true under any continuous performance metric in the transient regime as well as for the steady-state if the model is exponentially stable. To go one step further, we derive a bias correction term for the steady-state from which we define a new approximation called the refined `average' mean field approximation whose bias is of order $O(1/N^2)$. This refined `average' mean field approximation allows computing an accurate approximation even for small scaling factors, i.e., $N\approx 10 -50$. We illustrate the developed framework and accuracy results through an application to a random access CSMA model.Comment: 28 page

rmftool - A library to Compute (Refined) Mean Field Approximation(s)

International audienceMean field approximation is a powerful technique to study the performance of large stochastic systems represented as systems of interacting objects. Applications include load balancing models, epidemic spreading, cache replacement policies, or large-scale data centers, for which mean field approximation gives very accurate estimates of the transient or steady-state behaviors. In a series of recent papers [9, 7], a new and more accurate approximation, called the refined mean field approximation is presented. Yet, computing this new approximation can be cumbersome. The purpose of this paper is to present a tool, called rmf tool, that takes the description of a mean field model, and can numerically compute its mean field approximations and refinement

Real-world management of macular edema secondary to retinal vein occlusion with intravitreal aflibercept: 24-month results from the AURIGA observational study

Introduction: AURIGA is the largest real-world study to date to evaluate intravitreal aflibercept (IVT-AFL) treatment of diabetic macular edema or macular edema secondary to retinal vein occlusion (RVO) in routine clinical practice. Here, we report the 24-month outcomes in the RVO cohort from France, Germany, Italy, and Taiwan.MethodsAURIGA (NCT03161912) was a prospective observational study. Eligible patients with RVO were enrolled for whom the decision to treat with IVT-AFL had already been made by the attending physician. Patients were treated with IVT-AFL for up to 24 months at physician discretion according to local practice. The primary endpoint was mean change in visual acuity (VA; Early Treatment Diabetic Retinopathy Study [ETDRS] letters) from baseline to month (M) 12. All statistical analyses were descriptive.ResultsIn 554 treatment-naive and 65 previously treated patients with RVO, the respective mean (95% confidence interval) change in VA from baseline was + 12.5 (10.8, 14.3) and + 7.9 (3.3, 12.6) letters by M12 and + 11.4 (9.4, 13.3) and + 4.4 (- 0.6, 9.5) letters by M24 (baseline mean +/- standard deviation: 51.0 +/- 21.9 and 51.9 +/- 20.4 letters); 44.0% of treatment-naive and 27.9% of previously treated patients reported >= 15-letter gains by M24. By M24, the mean change in central retinal thickness from baseline was - 247 (- 267, - 227) mu m in treatment-naive patients and - 147 (- 192, - 102) mu m in previously treated patients. From baseline to M6, M12, and M24, treatment-naive patients received a total of 4.0 +/- 1.3, 5.5 +/- 2.5, and 6.9 +/- 4.2 injections, respectively, and previously treated patients received 3.8 +/- 1.5, 5.0 +/- 2.2, and 6.3 +/- 3.7 injections, respectively. The safety profile of IVT-AFL was consistent with that of previous studies.ConclusionsIn AURIGA, patients with RVO experienced clinically relevant functional and anatomic improvements following IVT-AFL treatment in routine clinical practice. These improvements were largely maintained in treatment-naive patients over the 24-month study despite the decreasing treatment frequency, suggesting long-term durability of IVT-AFL treatment outcomes. Infographic available for this article.Trial RegistrationClinicalTrials.gov Identifier: NCT03161912 (May 19, 2017)

Patients with Neovascular Age-Related Macular Degeneration Requiring Intensive Intravitreal Aflibercept Treatment: An ARIES Post Hoc Analysis.

INTRODUCTION The aim of this post hoc analysis of the ARIES study is to explore the requirement for intravitreal aflibercept (IVT-AFL) treatment intervals of < 8 weeks (w) in patients with neovascular age-related macular degeneration (nAMD), and to assess vision and anatomic outcomes in such patients who require more intensive treatment. METHODS ARIES was a multicenter, randomized, phase 3b/4 study that investigated the efficacy of two IVT-AFL proactive, individualized, treat-and-extend regimens over 2 years in treatment-naïve patients with nAMD. Patients were determined as injection-intensive if the study investigator identified that a treatment interval of < 8 w was needed and if they had ≥ 1 interval of < 8 w after three initial monthly doses. Treatment intervals could be extended subsequently if extension criteria were met. This is a post hoc analysis of patients enrolled in ARIES and statistical analysis is descriptive. RESULTS Of 269 patients in the combined treatment arms, 23.0% (n = 62) were injection-intensive (Year 1: 13.8% [n = 37]; Year 2: 9.3% [n = 25]). Time from IVT-AFL initiation to injection-intensive determination varied (range, 16-100 w; median: 43.2 w). Mean treatment interval was 8.4 w before and 6.1 w after injection-intensive determination. Overall, 59.7% achieved treatment intervals of ≥ 8 w following injection-intensive determination. Vision improvements from baseline to Week 104 were smaller for injection-intensive patients than non-injection-intensive patients (mean [SD] best-corrected visual acuity change: + 2.3 [15.6] vs.  + 5.9 [12.3] letters). Anatomic outcomes were similar between injection-intensive and non-injection-intensive patients (central retinal thickness change from baseline to Week 104: - 160 [154] vs.  - 167 [136] µm). CONCLUSIONS In ARIES, 23% of treatment-naïve patients with nAMD experienced at least one treatment interval of < 8 w. Injection-intensive patients showed improved vision and anatomic outcomes. For most, treatment intervals could be extended to ≥ 8 w following injection-intensive determination. CLINICALTRIALS gov Identifier: NCT02581891

Association Between Visual Acuity and Fluid Compartments with Treat-and-Extend Intravitreal Aflibercept in Neovascular Age-Related Macular Degeneration: An ARIES Post Hoc Analysis.

INTRODUCTION Recently, there has been growing interest in exploring the relationship between visual acuity and fluid localization in different retinal compartments. This post hoc analysis of the ARIES study explores the relationship between the presence of intraretinal fluid (IRF) and subretinal fluid (SRF), both at baseline and throughout treatment, and best-corrected visual acuity (BCVA) in patients with neovascular age-related macular degeneration (nAMD) treated with intravitreal aflibercept (IVT-AFL) in a treat-and-extend regimen. METHODS ARIES (NCT02581891) was a multicenter, randomized, phase 3b/4 study comparing the efficacy of two IVT-AFL treat-and-extend regimens over 2 years in patients with treatment-naïve nAMD. This post hoc analysis explores the relationship between the presence of SRF/IRF and absolute BCVA (letter score) at baseline and fixed visits. RESULTS In 210 patients (treat-and-extend treatment arms combined), SRF presence at baseline was associated at every time point with a numerically higher mean BCVA than if absent, with 10 more letters at week 104. IRF presence at baseline was associated at all but one time point with a numerically lower mean BCVA than if absent (week 104, 8-letter difference). Baseline SRF+IRF was associated with lower BCVA (week 104, 7-letter difference) than if only SRF was present, but higher BCVA (week 104, 8-letter difference) than if only IRF was present. Absence of SRF+IRF was not associated with better BCVA at any time point during the study. CONCLUSION In ARIES, in patients with nAMD treated with IVT-AFL, the presence of SRF was associated with better visual acuity, whereas IRF was associated with poorer visual acuity. The findings of this post hoc analysis suggest that differentiating IRF from SRF may offer better prognostic value in guiding treatment-extension decisions than the use of combined or "any" IRF and SRF. Prospective trials are needed to validate these results and determine their clinical relevance. TRIAL REGISTRATION NUMBER (CLINICALTRIALS.GOV): NCT02581891. Association between Visual Acuity and Fluid Compartments with Treat-and-Extend Intravitreal Aflibercept in Neovascular Age-Related Macular Degeneration: An ARIES Post Hoc Analysis: A Video Abstract (MP4 308264 KB)

Intravitreal Aflibercept for the treatment of diabetic macular edema in routine clinical practice: results from the 24-Month AURIGA observational study

Introduction AURIGA is the largest real-world study to date to evaluate intravitreal aflibercept (IVT-AFL) in the treatment of diabetic macular edema (DME) or macular edema secondary to retinal vein occlusion in routine clinical practice. The 24-month outcomes in the DME cohort from across 11 participating countries are reported here.MethodsAURIGA (NCT03161912) was a prospective observational study. The study enrolled eligible patients with DME for whom the decision to treat with IVT-AFL had previously been made by the attending physician. Patients were treated with IVT-AFL for up to 24 months at physician discretion according to local practice. The primary endpoint was mean change in visual acuity (VA; Early Treatment Diabetic Retinopathy Study [ETDRS] letters) from baseline to month 12 (M12). All statistical analyses were descriptive.ResultsIn 1478 treatment-naive and 384 previously treated patients with DME, the mean (95% confidence interval) change in VA from baseline was +6.7 (5.7, 7.6) and +7.4 (5.5, 9.4) letters by M12 and +5.9 (4.9, 6.9) and +8.1 (6.1, 10.1) letters by M24 (baseline [mean +/- standard deviation]: 56.0 +/- 19.8 and 50.8 +/- 19.5 letters), respectively; 25.9% of treatment-naive and 32.8% of previously treated patients achieved &gt;= 15-letter gains by M24. The mean change in central retinal thickness from baseline to M24 was -110 (-119, -102) mu m in treatment-naive patients and -169 (-188, -151) mu m in previously treated patients. By M6, M12, and M24, treatment-naive patients had received 3.8 +/- 1.7, 4.9 +/- 2.8, and 5.7 +/- 3.9 injections, respectively, and previously treated patients had received 3.9 +/- 1.5, 4.9 +/- 2.4, and 6.2 +/- 3.6 injections, respectively. The safety profile of IVT-AFL was consistent with previous studies.ConclusionIn AURIGA, treatment-naive and previously treated patients with DME achieved clinically relevant functional and anatomic improvements following IVT-AFL treatment for up to 24 months in routine clinical practice. Even with the decreasing injection frequency observed, these gains were largely maintained throughout the study, suggesting long-term durability of the positive effects of IVT-AFL treatment. Infographic available for this article.Trial RegistrationClinicalTrials.gov Identifier: NCT03161912 (May 19, 2017)

Ophthalmol Ther

INTRODUCTION: XTEND (NCT03939767) is a multicenter, observational, prospective study of patients with treatment-naïve neovascular age-related macular degeneration (nAMD) in routine clinical practice. The study aims to examine treatment outcomes of proactive intravitreal aflibercept (IVT-AFL) treatment regimens (fixed dosing or treat-and-extend) according to local marketing labels. METHODS: Study eyes received IVT-AFL injections as per the local label. The mean changes in best-corrected visual acuity (BCVA) and central subfield thickness (CST) from baseline to month (M) 12 and M24 were measured and stratified by baseline factors. Treatment exposure and safety data were evaluated. Statistical analysis was descriptive. RESULTS: Overall, 1466 patients from 17 countries were treated. For the overall population, the mean ± standard deviation (SD) age was 78.7 ± 8.5 (range 50-100) years, and 891 patients (60.8%) were female. The mean ± SD baseline BCVA was 54.3 ± 20.3 letters and CST was 374 ± 126 µm. At M12 and M24, mean (95% confidence interval [CI]) BCVA change was + 4.3 (3.4, 5.3) and + 2.3 (1.3, 3.3) letters, respectively. Mean (95% CI) CST was - 106 (- 114, - 99) μm and - 109 (- 117, - 102) μm at M12 and M24, respectively. At M24, 41.5% of patients had a BCVA ≥ 70 letters. Patients received a mean ± SD of 7.7 ± 2.7 injections by M12 and 10.8 ± 5.0 injections by M24 (3.1 injections between M12 and M24). Adverse events were consistent with the known safety profile of IVT-AFL. CONCLUSION: The 24-month results indicate that, in routine clinical practice, a proactive IVT-AFL regimen achieves functional improvements in patients with treatment-naïve nAMD. The proportion of patients achieving ≥ 70 letters at M24 increased, and patients with baseline BCVA ≥ 70 letters maintained vision regardless of the followed IVT-AFL label. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03939767. A video abstract is available for this article. Supplementary file2 (MP4 364624 KB)

Antimicrobial Resistance in Escherichia coli

Multidrug resistance in Escherichia coli has become a worrying issue that is increasingly observed in human but also in veterinary medicine worldwide. E. coli is intrinsically susceptible to almost all clinically relevant antimicrobial agents, but this bacterial species has a great capacity to accumulate resistance genes, mostly through horizontal gene transfer. The most problematic mechanisms in E. coli correspond to the acquisition of genes coding for extended-spectrum β-lactamases (conferring resistance to broad-spectrum cephalosporins), carbapenemases (conferring resistance to carbapenems), 16S rRNA methylases (conferring pan-resistance to aminoglycosides), plasmid-mediated quinolone resistance (PMQR) genes (conferring resistance to [fluoro]quinolones), and mcr genes (conferring resistance to polymyxins). Although the spread of carbapenemase genes has been mainly recognized in the human sector but poorly recognized in animals, colistin resistance in E. coli seems rather to be related to the use of colistin in veterinary medicine on a global scale. For the other resistance traits, their cross-transfer between the human and animal sectors still remains controversial even though genomic investigations indicate that extended- spectrum β-lactamase producers encountered in animals are distinct from those affecting humans. In addition, E. coli of animal origin often also show resistances to other—mostly older—antimicrobial agents, including tetracyclines, phenicols, sulfonamides, trimethoprim, and fosfomycin. Plasmids, especially multiresistance plasmids, but also other mobile genetic elements, such as transposons and gene cassettes in class 1 and class 2 integrons, seem to play a major role in the dissemination of resistance genes. Of note, coselection and persistence of resistances to critically important antimicrobial agents in human medicine also occurs through the massive use of antimicrobial agents in veterinary medicine, such as tetracyclines or sulfonamides, as long as all those determinants are located on the same genetic elements