Quantitative microbial risk assessment for ingestion of antibiotic resistance genes from private wells contaminated by human and livestock fecal sources.

We used quantitative microbial risk assessment to estimate ingestion risk for intI1, erm(B), sul1, tet(A), tet(W), and tet(X) in private wells contaminated by human and/or livestock feces. Genes were quantified with five human-specific and six bovine-specific microbial source-tracking (MST) markers in 138 well-water samples from a rural Wisconsin county. Daily ingestion risk (probability of swallowing ≥1 gene) was based on daily water consumption and a Poisson exposure model. Calculations were stratified by MST source and soil depth over the aquifer where wells were drilled. Relative ingestion risk was estimated using wells with no MST detections and >6.1 m soil depth as a referent category. Daily ingestion risk varied from 0 to 8.8 × 10-1 by gene and fecal source (i.e., human or bovine). The estimated number of residents ingesting target genes from private wells varied from 910 (tet(A)) to 1,500 (intI1 and tet(X)) per day out of 12,000 total. Relative risk of tet(A) ingestion was significantly higher in wells with MST markers detected, including wells with ≤6.1 m soil depth contaminated by bovine markers (2.2 [90% CI: 1.1-4.7]), wells with >6.1 m soil depth contaminated by bovine markers (1.8 [1.002-3.9]), and wells with ≤6.1 m soil depth contaminated by bovine and human markers simultaneously (3.1 [1.7-6.5]). Antibiotic resistance genes (ARGs) were not necessarily present in viable microorganisms, and ingestion is not directly associated with infection. However, results illustrate relative contributions of human and livestock fecal sources to ARG exposure and highlight rural groundwater as a significant point of exposure.IMPORTANCEAntibiotic resistance is a global public health challenge with well-known environmental dimensions, but quantitative analyses of the roles played by various natural environments in transmission of antibiotic resistance are lacking, particularly for drinking water. This study assesses risk of ingestion for several antibiotic resistance genes (ARGs) and the class 1 integron gene (intI1) in drinking water from private wells in a rural area of northeast Wisconsin, United States. Results allow comparison of drinking water as an exposure route for antibiotic resistance relative to other routes like food and recreational water. They also enable a comparison of the importance of human versus livestock fecal sources in the study area. Our study demonstrates the previously unrecognized importance of untreated rural drinking water as an exposure route for antibiotic resistance and identifies bovine fecal material as an important exposure factor in the study setting.

Synthesis of (-)-Cotylenol, a 14-3-3 Molecular Glue Component.

Small molecules that modulate the 14-3-3 protein-protein interaction (PPI) network represent valuable therapeutics and tool compounds. However, access has been lost to 14-3-3 PPI molecular glues of the cotylenin class, leading to investigations into the practical chemical syntheses of congeners and analogues. Here we report a concise synthesis of (-)-cotylenol via a 10-step asymmetric entry into a diversifiable 5-8-5 core. This route features a mild Liebeskind-Srogl fragment coupling that tolerates unprecedented steric hindrance to produce a highly congested ketone, and a tandem Claisen-ene cascade that establishes the 8-membered ring. Late-stage control of stereochemistry and functionality leads to (-)-cotylenol and sets the stage for focused library synthesis.

Community intervention trial for estimating risk of acute gastrointestinal illness from groundwater-supplied non-disinfected drinking water.

By community intervention in 14 non-disinfecting municipal water systems, we quantified sporadic acute gastrointestinal illness (AGI) attributable to groundwater. Ultraviolet (UV) disinfection was installed on all supply wells of intervention communities. In control communities, residents continued to drink non-disinfected groundwater. Intervention and control communities switched treatments by moving UV disinfection units at the study midpoint (crossover design). Study participants (n = 1,659) completed weekly health diaries during four 12-week surveillance periods. Water supply wells were analyzed monthly for enteric pathogenic viruses. Using the crossover design, groundwater-borne AGI was not observed. However, virus types and quantity in supply wells changed through the study, suggesting that exposure was not constant. Alternatively, we compared AGI incidence between intervention and control communities within the same surveillance period. During Period 1, norovirus contaminated wells and AGI attributable risk from well water was 19% (95% CI, -4%, 36%) for children <5 years and 15% (95% CI, -9%, 33%) for adults. During Period 3, echovirus 11 contaminated wells and UV disinfection slightly reduced AGI in adults. Estimates of AGI attributable risks from drinking non-disinfected groundwater were highly variable, but appeared greatest during times when supply wells were contaminated with specific AGI-etiologic viruses.

Adult Attention-Deficit/Hyperactivity Disorder: a Narrative Review of Biological Mechanisms, Treatments, and Outcomes.

PURPOSE OF REVIEW: Attention-deficit/hyperactivity disorder (ADHD) is a heterogeneous and complex neurodevelopmental disorder related to disruptions in various neuronal structures and pathways, dopamine (DA) transporter, and receptor genes, resulting in cognitive and regulation deficits. This article reviews recent research on the biological mechanisms and markers, clinical manifestations, treatments, and outcomes of adult ADHD as well as current controversies within the field. RECENT FINDINGS: New research identifies white matter disruptions in multiple cortical pathways in adults with ADHD. New treatments for ADHD in adults such as viloxazine ER have shown preliminary effectiveness in addition to research showing transcranial direct current stimulation can be an effective treatment for adults with ADHD. Although questions exist about the effectiveness of current assessments of and treatments for adult ADHD, recent findings represent a step towards improving the quality of life and outcomes for individuals experiencing this life-long, chronic health condition.

Child, parent, and family mental health and functioning in Australia during COVID-19: comparison to pre-pandemic data.

The COVID-19 pandemic presents significant risks to population mental health. Despite evidence of detrimental effects for adults, there has been limited examination of the impact of COVID-19 on parents and children specifically. We aim to examine patterns of parent and child (0-18 years) mental health, parent substance use, couple conflict, parenting practices, and family functioning during COVID-19, compared to pre-pandemic data, and to identify families most at risk of poor outcomes according to pre-existing demographic and individual factors, and COVID-19 stressors. Participants were Australian mothers (81%) and fathers aged 18 years and over who were parents of a child 0-18 years (N = 2365). Parents completed an online self-report survey during 'stage three' COVID-19 restrictions in April 2020. Data were compared to pre-pandemic data from four Australian population-based cohorts. Compared to pre-pandemic estimates, during the pandemic period parents reported higher rates of parent depression, anxiety, and stress (Cohen's d = 0.26-0.81, all p < 0.001), higher parenting irritability (d = 0.17-0.46, all p < 0.001), lower family positive expressiveness (d = - 0.18, p < 0.001), and higher alcohol consumption (22% vs 12% drinking four or more days per week, p < 0.001). In multivariable analyses, we consistently found that younger parent age, increased financial deprivation, pre-existing parent and child physical and mental health conditions, COVID-19 psychological and environmental stressors, and housing dissatisfaction were associated with worse parent and child functioning and more strained family relationships. Our data suggest wide-ranging, detrimental family impacts associated with the COVID-19 pandemic; and support policy actions to assist families with financial supports, leave entitlements, and social housing.

Variations of accessory thoracic muscles identified in the ethnically diverse whole-body donation population in Northern California.

Accessory thoracic muscles in humans are relatively common and it is important to draw awareness to their variable presentations and potential clinical implications owing to their close association with the axilla. Here we report four cases of accessory thoracic muscle variations identified in the ethnically diverse whole- -body donation population in Northern California (4 out of 48 donors, 8.3%). Of these, combined presentations of thoracic accessory muscles were observed in two of the donors, one involving bilateral axillary arches and a pectoralis quartus on the left and the other a unilateral axillary arch on the left and bilateral pairs of pectoral fascicles. In the former, the proximal ends of the left axillary arch and pectoralis quartus joined to form a common aponeurosis which inserted onto the deep tendon of the pectoralis major; in the latter, the pectoral fascicles originated from the surface of the ribs and inserted into the deep surface of the pectoralis major muscle. In the other two donors, unilateral axillary arches were observed. Our observations illustrate that accessory thoracic muscles, in isolated as well as combined forms, are commonplace in the general population. We also describe the proposed embryonic origins of these accessory muscles, which may reflect their frequent occurrence, and potential clinical implications of these muscles, as discussed in literature.

Microbial source tracking and land use associations for antibiotic resistance genes in private wells influenced by human and livestock fecal sources.

Antimicrobial resistance is a growing public health problem that requires an integrated approach among human, agricultural, and environmental sectors. However, few studies address all three components simultaneously. We investigated the occurrence of five antibiotic resistance genes (ARGs) and the class 1 integron gene (intI1) in private wells drawing water from a vulnerable aquifer influenced by residential septic systems and land-applied dairy manure. Samples (n = 138) were collected across four seasons from a randomized sample of private wells in Kewaunee County, Wisconsin. Measurements of ARGs and intI1 were related to microbial source tracking (MST) markers specific to human and bovine feces; they were also related to 54 risk factors for contamination representing land use, rainfall, hydrogeology, and well construction. ARGs and intI1 occurred in 5%-40% of samples depending on target. Detection frequencies for ARGs and intI1 were lowest in the absence of human and bovine MST markers (1%-30%), highest when co-occurring with human and bovine markers together (11%-78%), and intermediate when co-occurring with just one type of MST marker (4%-46%). Gene targets were associated with septic system density more often than agricultural land, potentially because of the variable presence of manure on the landscape. Determining ARG prevalence in a rural setting with mixed land use allowed an assessment of the relative contribution of human and bovine fecal sources. Because fecal sources co-occurred with ARGs at similar rates, interventions intended to reduce ARG occurrence may be most effective if both sources are considered.

The World Rugby and International Rugby Players Contact Load Guidelines: From conception to implementation and the future.

Managing training load in rugby union is crucial for optimising performance and injury prevention. Contact training warrants attention because of higher overall injury and head impact risk, yet players must develop physical, technical, and mental skills to withstand the demands of the game. To help coaches manage contact loads in professional rugby, World Rugby and International Rugby Players convened an expert working group. They conducted a global survey with players to develop contact load guidelines. This commentary aims to describe the contact load guidelines and their implementation, and identify areas where future work is needed to support their evolution.

Quantifying CrossFit®: Potential solutions for monitoring multimodal workloads and identifying training targets.

The design of high-intensity functional training (HIFT; e. g., CrossFit®) workouts and targeted physiological trait(s) vary on any given training day, week, or cycle. Daily workouts are typically comprised of different modality and exercise combinations that are prescribed across a wide range of intensities and durations. The only consistent aspect appears to be the common instruction to maximize effort and workout density by either completing "as many repetitions as possible" within a time limit (e.g., AMRAP, Tabata) or a list of exercises as quickly as possible. However, because effort can vary within and across workouts, the impact on an athlete's physiology may also vary daily. Programming that fails to account for this variation or consider how targeted physiological systems interrelate may lead to overuse, maladaptation, or injury. Athletes may proactively monitor for negative training responses, but any observed response must be tied to a quantifiable workload before meaningful changes (to programming) are possible. Though traditional methods exist for quantifying the resistance training loads, gymnastic movements, and cardiorespiratory modalities (e.g., cycling running) that might appear in a typical HIFT workout, those methods are not uniform, and their meaning will vary based on a specific exercise's placement within a HIFT workout. To objectively quantify HIFT workloads, the calculation must overcome differences in measurement standards used for each modality, be able to account for a component's placement within the workout and be useful regardless of how a workout is commonly scored (e.g., repetitions completed vs. time-to-completion) so that comparisons between workouts are possible. This review paper discusses necessary considerations for quantifying various HIFT workout components and structures, and then details the advantages and shortcomings of different methods used in practice and the scientific literature. Methods typically used in practice range from being excessively tedious and not conducive for making comparisons within or across workouts, to being overly simplistic, based on faulty assumptions, and inaccurate. Meanwhile, only a few HIFT-related studies have attempted to report relevant workloads and have predominantly relied on converting component and workout performance into a rate (i.e., repetitions per minute or second). Repetition completion rate may be easily and accurately tracked and allows for intra- and inter-workout comparisons. Athletes, coaches, and sports scientists are encouraged to adopt this method and potentially pair it with technology (e.g., linear position transducers) to quantify HIFT workloads. Consistent adoption of such methods would enable more precise programming alterations, and it would allow fair comparisons to be made between existing and future research.

Hexagonal silicon-germanium nanowire branches with tunable composition.

Hexagonal SiGe-2H has been recently shown to have a direct bandgap, and holds the promise to be compatible with silicon technology. Hexagonal Si and Ge have been grown on an epitaxial lattice matched template consisting of wurtzite GaP and GaAs, respectively. Here, we present the growth of hexagonal Si and SiGe nanowire branches grown from a wurtzite stem by the vapor-liquid-solid growth mode, which is substantiated byin situtransmission electron microscopy. We show that the composition can be tuned through the whole range of stoichiometry from Si to Ge, and the possibility to realize Si and SiGe heterostructures in these branches.

Association of Maternal Versus Fetal Ehlers-Danlos Syndrome Status with Poor Pregnancy Outcomes.

The majority of research papers published on obstetrical outcomes in Ehlers-Danlos syndrome (EDS) have focused on the contribution of maternal EDS to the risk of poor pregnancy outcomes. The purpose of our study was to further clarify the fetal versus maternal contribution of EDS to poor pregnancy outcomes. A web-based, anonymous questionnaire was developed to collect pregnancy histories of families with a member with EDS. The survey was disseminated via social media through the Ehlers Danlos National Foundation. Population descriptors (age, gender, EDS diagnosis, age of diagnosis) and pregnancy descriptors (number of pregnancies, live births, and birth complications) were collected. To identify fetal and maternal contribution of EDS to poor pregnancy outcomes, three groups were compared based on maternal or infant diagnosis (EDS versus non-EDS). The rate of birth complications, treatment for preterm birth, and occurrence of preterm birth, as well as gestational age at preterm birth, were different depending on maternal/ infant EDS status, and these differences were significant when comparing infant EDS status but not when comparing maternal EDS status. The occurrence of PPROM is increased in the non-EDS mother/EDS infant group compared to both EDS mother/non-EDS infant and EDS mother/EDS infant groups (38.9%, 12.5%, 14.8%, p = 0.025). This study identifies that poor outcomes in EDS pregnancies differ depending on the maternal and the fetal EDS status. These insights into maternal and fetal association with certain poor pregnancy outcomes in pregnancies complicated by EDS can further guide physicians in educating, managing, and treating these women during pregnancy.

Statewide Quantitative Microbial Risk Assessment for Waterborne Viruses, Bacteria, and Protozoa in Public Water Supply Wells in Minnesota.

Infection risk from waterborne pathogens can be estimated via quantitative microbial risk assessment (QMRA) and forms an important consideration in the management of public groundwater systems. However, few groundwater QMRAs use site-specific hazard identification and exposure assessment, so prevailing risks in these systems remain poorly defined. We estimated the infection risk for 9 waterborne pathogens based on a 2-year pathogen occurrence study in which 964 water samples were collected from 145 public wells throughout Minnesota, USA. Annual risk across all nine pathogens combined was 3.3 × 10-1 (95% CI: 2.3 × 10-1 to 4.2 × 10-1), 3.9 × 10-2 (2.3 × 10-2 to 5.4 × 10-2), and 1.2 × 10-1 (2.6 × 10-2 to 2.7 × 10-1) infections person-1 year-1 for noncommunity, nondisinfecting community, and disinfecting community wells, respectively. Risk estimates exceeded the U.S. benchmark of 10-4 infections person-1 year-1 in 59% of well-years, indicating that the risk was widespread. While the annual risk for all pathogens combined was relatively high, the average daily doses for individual pathogens were low, indicating that significant risk results from sporadic pathogen exposure. Cryptosporidium dominated annual risk, so improved identification of wells susceptible to Cryptosporidium contamination may be important for risk mitigation.

Fate and seasonality of antimicrobial resistance genes during full-scale anaerobic digestion of cattle manure across seven livestock production facilities.

Anaerobic digestion has been suggested as an intervention to attenuate antibiotic resistance genes (ARGs) in livestock manure but supporting data have typically been collected at laboratory scale. Few studies have quantified ARG fate during full-scale digestion of livestock manure. We sampled untreated manure and digestate from seven full-scale mesophilic dairy manure digesters to assess ARG fate through each system. Samples were collected biweekly from December through August (i.e., winter, spring, and summer; n = 235 total) and analyzed by quantitative polymerase chain reaction for intI1, erm(B), sul1, tet(A), and tet(W). Concentrations of intI1, sul1, and tet(A) decreased during anaerobic digestion, but their removal was less extensive than expected based on previous laboratory studies. Removal for intI1 during anaerobic digestion equaled 0.28 ± 0.03 log10 units (mean ± SE), equivalent to only 48% removal and notable given intI1's role in horizontal gene transfer and multiple resistance. Furthermore, tet(W) concentrations were unchanged during anaerobic digestion (p > 0.05), and erm(B) concentrations increased by 0.52 ± 0.03 log10 units (3.3-fold), which is important given erythromycin's status as a critically important antibiotic for human medicine. Seasonal log10 changes in intI1, sul1, and tet(A) concentrations were ≥50% of corresponding log10 removals by anaerobic digestion, and variation in ARG and intI1 concentrations among digesters was quantitatively comparable to anaerobic digestion effects. These results suggest that mesophilic anaerobic digestion may be limited as an intervention for ARGs in livestock manure and emphasize the need for multiple farm-level interventions to attenuate antibiotic resistance.

Artificial Intelligence: Guidance for clinical imaging and therapeutic radiography professionals, a summary by the Society of Radiographers AI working group.

INTRODUCTION: Artificial intelligence (AI) has started to be increasingly adopted in medical imaging and radiotherapy clinical practice, however research, education and partnerships have not really caught up yet to facilitate a safe and effective transition. The aim of the document is to provide baseline guidance for radiographers working in the field of AI in education, research, clinical practice and stakeholder partnerships. The guideline is intended for use by the multi-professional clinical imaging and radiotherapy teams, including all staff, volunteers, students and learners. METHODS: The format mirrored similar publications from other SCoR working groups in the past. The recommendations have been subject to a rapid period of peer, professional and patient assessment and review. Feedback was sought from a range of SoR members and advisory groups, as well as from the SoR director of professional policy, as well as from external experts. Amendments were then made in line with feedback received and a final consensus was reached. RESULTS: AI is an innovative tool radiographers will need to engage with to ensure a safe and efficient clinical service in imaging and radiotherapy. Educational provisions will need to be proportionately adjusted by Higher Education Institutions (HEIs) to offer the necessary knowledge, skills and competences for diagnostic and therapeutic radiographers, to enable them to navigate a future where AI will be central to patient diagnosis and treatment pathways. Radiography-led research in AI should address key clinical challenges and enable radiographers co-design, implement and validate AI solutions. Partnerships are key in ensuring the contribution of radiographers is integrated into healthcare AI ecosystems for the benefit of the patients and service users. CONCLUSION: Radiography is starting to work towards a future with AI-enabled healthcare. This guidance offers some recommendations for different areas of radiography practice. There is a need to update our educational curricula, rethink our research priorities, forge new strong clinical-academic-industry partnerships to optimise clinical practice. Specific recommendations in relation to clinical practice, education, research and the forging of partnerships with key stakeholders are discussed, with potential impact on policy and practice in all these domains. These recommendations aim to serve as baseline guidance for UK radiographers. IMPLICATIONS FOR PRACTICE: This review offers the most up-to-date recommendations for clinical practitioners, researchers, academics and service users of clinical imaging and therapeutic radiography services. Radiography practice, education and research must gradually adjust to AI-enabled healthcare systems to ensure gains of AI technologies are maximised and challenges and risks are minimised. This guidance will need to be updated regularly given the fast-changing pace of AI development and innovation.

Quantitative Microbial Risk Assessment for Contaminated Private Wells in the Fractured Dolomite Aquifer of Kewaunee County, Wisconsin.

BACKGROUND: Private wells are an important source of drinking water in Kewaunee County, Wisconsin. Due to the region's fractured dolomite aquifer, these wells are vulnerable to contamination by human and zoonotic gastrointestinal pathogens originating from land-applied cattle manure and private septic systems. OBJECTIVE: We determined the magnitude of the health burden associated with contamination of private wells in Kewaunee County by feces-borne gastrointestinal pathogens. METHODS: This study used data from a year-long countywide pathogen occurrence study as inputs into a quantitative microbial risk assessment (QMRA) to predict the total cases of acute gastrointestinal illness (AGI) caused by private well contamination in the county. Microbial source tracking was used to associate predicted cases of illness with bovine, human, or unknown fecal sources. RESULTS: Results suggest that private well contamination could be responsible for as many as 301 AGI cases per year in Kewaunee County, and that 230 and 12 cases per year were associated with a bovine and human fecal source, respectively. Furthermore, Cryptosporidium parvum was predicted to cause 190 cases per year, the most out of all 8 pathogens included in the QMRA. DISCUSSION: This study has important implications for land use and water resource management in Kewaunee County and informs the public health impacts of consuming drinking water produced in other similarly vulnerable hydrogeological settings. https://doi.org/10.1289/EHP7815.

Sources and Risk Factors for Nitrate and Microbial Contamination of Private Household Wells in the Fractured Dolomite Aquifer of Northeastern Wisconsin.

BACKGROUND: Groundwater quality in the Silurian dolomite aquifer in northeastern Wisconsin, USA, has become contentious as dairy farms and exurban development expand. OBJECTIVES: We investigated private household wells in the region, determining the extent, sources, and risk factors of nitrate and microbial contamination. METHODS: Total coliforms, Escherichia coli, and nitrate were evaluated by synoptic sampling during groundwater recharge and no-recharge periods. Additional seasonal sampling measured genetic markers of human and bovine fecal-associated microbes and enteric zoonotic pathogens. We constructed multivariable regression models of detection probability (log-binomial) and concentration (gamma) for each contaminant to identify risk factors related to land use, precipitation, hydrogeology, and well construction. RESULTS: Total coliforms and nitrate were strongly associated with depth-to-bedrock at well sites and nearby agricultural land use, but not septic systems. Both human wastewater and cattle manure contributed to well contamination. Rotavirus group A, Cryptosporidium, and Salmonella were the most frequently detected pathogens. Wells positive for human fecal markers were associated with depth-to-groundwater and number of septic system drainfield within 229m. Manure-contaminated wells were associated with groundwater recharge and the area size of nearby agricultural land. Wells positive for any fecal-associated microbe, regardless of source, were associated with septic system density and manure storage proximity modified by bedrock depth. Well construction was generally not related to contamination, indicating land use, groundwater recharge, and bedrock depth were the most important risk factors. DISCUSSION: These findings may inform policies to minimize contamination of the Silurian dolomite aquifer, a major water supply for the U.S. and Canadian Great Lakes region. https://doi.org/10.1289/EHP7813.

Revealing time's secrets at the National Theatre of Costa Rica via innovative software for cultural heritage research.

Establishing affordable, efficient, accessible, innovative, and multidisciplinary methodologies to the diagnosis of the conservation state of an artwork is key to carry out appropriate strategies of conservation and consequently to the creation of modern public policies on cultural heritage. Limited access to large-format paintings is a challenge to restoration scientists seeking to obtain information quickly, in a non-destructive and non-invasive manner, and identify regions of interest. Therefore, we put forward two unique software tools based on multispectral imaging techniques, with the long-term aim to assess the artist's intentions, creative process, and colour palette. This development paves the way for a comprehensive and multidisciplinary understanding of the mysteries encompassed in each pictorial layer, through the study of their physical and chemical characteristics. We conducted the first ever study on Musas I and Musas II, two large-format paintings by Italian artist Carlo Ferrario, located in the National Theatre of Costa Rica. In this study, we used our novel imaging techniques to choose regions of interest in order to study sample layers; while also assessing the works' state of conservation and possible biodeterioration. We explored the applications of our two versatile software tools, RegionOfInterest and CrystalDistribution, and confirmed paint stratigraphies by means of microscopy and spectroscopy analyses (OM, SEM-EDX, Fluorescent microscopy, FTIR-ATR and micro-Raman). In a pilot study, we identified the artist's main colour palette: zinc white, lead white, chrome yellow, lead read, viridian, along with artificial vermilion and ultramarine pigments. We were able to identify artificial vermilion and ultramarine and distinguish them from the natural pigments using CrystalDistribution to map the average size and diameter of the pigment crystals within the paint layers. This study demonstrated that software-based multidisciplinary imaging techniques are novel in establishing preventive and non-invasive methods for historical painting conservation studies, in addition, this study provides tools with great potential to be used in the future in applications such as virtual restoration.

Sport Concussion Assessment Tool: baseline and clinical reference limits for concussion diagnosis and management in elite Rugby Union.

OBJECTIVES: Rugby Union has adapted the Sports Concussion Assessment Tool (SCAT) into an abridged off-field concussion screen and the complete SCAT is used during diagnostic screens performed after head impact events. No firm guidelines exist as to what should be considered "abnormal" and warrant further evaluation. This study evaluates SCAT performances in 13,479 baseline SCAT assessments, and proposes clear reference limits for each sub-component of the SCAT5. Baseline reference limits are proposed to guide management of baseline testing by identifying abnormal sub-tests, enhancing the clinical validity of baseline screens, while clinical reference limits are identified to support concussion diagnosis when no baseline is available. DESIGN: Cross sectional census sample. METHODS: 13,479 baseline SCATs from 7565 elite male rugby players were evaluated. Baseline reference limits were identified for each sub-test as the sub-test result achieved by approximately 5% of the population, while clinical references limits corresponded to the sub-test score achieved by as close as possible to 50% of the cohort. RESULTS: Players reported symptoms 35% (95% CI 1.29-1.42) more frequently during SCAT5 than SCAT3 baseline assessments (mean 1.4±2.7 vs 1.0±2.4). Ceiling effects were identified for many cognitive sub-tests within the SCAT. Baseline and Clinical reference limits corresponding to the worst performing 5th percentile and 50th percentile were described. CONCLUSIONS: Targeted baseline re-testing should be repeated when abnormal sub-tests are identified according to proposed baseline reference limits, while a more conservative clinical reference limit supports concussion diagnosis during screens in diagnostic settings.