To identify factors that regulate gut microbiota density and the impact of varied microbiota density on health, we assayed this fundamental ecosystem property in fecal samples across mammals, human disease, and therapeutic interventions. Physiologic features of the host (carrying capacity) and the fitness of the gut microbiota shape microbiota density. Therapeutic manipulation of microbiota density in mice altered host metabolic and immune homeostasis. In humans, gut microbiota density was reduced in Crohn’s disease, ulcerative colitis, and ileal pouch-anal anastomosis. The gut microbiota in recurrent Clostridium difficile infection had lower density and reduced fitness that were restored by fecal microbiota transplantation. Understanding the interplay between microbiota and disease in terms of microbiota density, host carrying capacity, and microbiota fitness provide new insights into microbiome structure and microbiome targeted therapeutics.Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

Fecal incontinence (FI) is a common gastrointestinal (GI) complaint in patients aged 65 years and older. This evidence-based review article discusses the epidemiology, pathophysiology, evaluation, and management of FI in the geriatric population. We emphasize aging-related changes leading to and impacting evaluation and treatment of this symptom while incorporating the core geriatric principles of functional status and management aligned with patient preference and goals of care.

Despite national and local governing board recommendations in the United States of America to perform an HCV screening test in baby boomers, screening rates remain low. Our goal was to study the impact of an HCV screening and link-to-care programme with patient navigation in two New York City primary care practices. This was a 2-year prospective study of patients born between 1945-1965 ("baby boomers") with encounters at two primary care practices at the Mount Sinai Hospital between November 1, 2013 and November 30, 2015. Baseline HCV screening rates were collected for four months. A multifaceted intervention was sequentially implemented involving electronic alerts, housestaff education, data feedback and patient navigation. HCV screening rates and link to care, defined as attending an appointment with a viral hepatitis specialist, were compared before and after these interventions. There were 14 642 primary care baby boomer patients of which 4419 (30.2%) were newly screened during the study. There was a significant increase in HCV screening rates from 55% to 75% (P<.01) with an HCV seropositive rate of 3.3%. Factors associated with being HCV seropositive included older age (P<.01), male sex (P<.01), African American race (P<.01) and receiving care in the housestaff practice (P<.01). With patient navigation, 78 of 84 (93%) newly diagnosed HCV-infected persons were referred to a specialist and 60 (77%) attended their first appointment. A structured, multifaceted HCV screening programme using well-studied principles identifies a large number of undiagnosed baby boomers within hospital-based primary care and improves access to specialty providers in a timely manner.

High-resolution microendoscopy (HRME) is a low-cost, “optical biopsy” technology that allows for subcellular imaging. The purpose of this study was to determine the in vivo diagnostic accuracy of the HRME for the differentiation of neoplastic from non-neoplastic colorectal polyps and compare it to that of high-definition white-light endoscopy (WLE) with histopathology as the gold standard. Three endoscopists prospectively detected a total of 171 polyps from 94 patients that were then imaged by HRME and classified in real-time as neoplastic (adenomatous, cancer) or non-neoplastic (normal, hyperplastic, inflammatory). HRME had a significantly higher accuracy (94%), specificity (95%), and positive predictive value (87%) for the determination of neoplastic colorectal polyps compared to WLE (65%, 39%, and 55%, respectively). When looking at small colorectal polyps (less than 10 mm), HRME continued to significantly outperform WLE in terms of accuracy (95% vs. 64%), specificity (98% vs. 40%) and positive predictive value (92% vs. 55%). These trends continued when evaluating diminutive polyps (less than 5 mm) as HRME's accuracy (95%), specificity (98%), and positive predictive value (93%) were all significantly greater than their WLE counterparts (62%, 41%, and 53%, respectively). In conclusion, this in vivo study demonstrates that HRME can be a very effective modality in the differentiation of neoplastic and non-neoplastic colorectal polyps. A combination of standard white-light colonoscopy for polyp detection and HRME for polyp classification has the potential to truly allow the endoscopist to selectively determine which lesions can be left in situ, which lesions can simply be discarded, and which lesions need formal histopathologic analysis.

Purpose Learners of medical procedures must develop, refine, and apply schemas for both cognitive and psychomotor constructs, which may strain working memory capacity. Procedures with limitations in visual and tactile information may add risk of cognitive overload. The authors sought to elucidate how experienced procedural teachers perceived learners’ challenges and their own teaching strategies in the exemplar setting of gastrointestinal endoscopy. Method The authors interviewed 22 experienced endoscopy teachers in the United States, Canada, and the Netherlands between May 2016 and March 2019 and performed thematic analysis using template analysis method. Interviews addressed learner challenges and teaching strategies from the teacher participants’ perspectives. Cognitive load theory informed data interpretation and analysis. Results Participants described taking steps to “diagnose” trainee ability and identify struggling trainees. They described learning challenges related to trainees (performance over mastery goal orientation, low self-efficacy, lack of awareness), tasks (psychomotor challenges, mental model development, tactile understanding), teachers (teacher–trainee relationship, inadequate teaching, teaching variability), and settings (internal/external distractions, systems issues). Participants described employing strategies that could match intrinsic load to learners’ levels (teaching along developmental continuum, motor instruction, technical assistance/takeover), minimize extraneous load (optimize environment, systems solutions, emotional support, define expectations), and optimize germane load (promote mastery, teach schemas, stop and focus). Conclusions Participants provided insight into possible challenges while learning complex medical procedures with limitations in sensory channels, as well as teaching strategies that may address these challenges at individual and systems levels. Using cognitive load theory, the authors provide recommendations for procedural teachers.