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ObjectivesTo evaluate prevention strategies, their unintended consequences and modifiable risk factors for sport-related concussion (SRC) and/or head impact risk.DesignThis systematic review and meta-analysis was registered on PROSPERO (CRD42019152982) and conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.Data sourcesEight databases (MEDLINE, CINAHL, APA PsycINFO, Cochrane (Systematic Review and Controlled Trails Registry), SPORTDiscus, EMBASE, ERIC0 were searched in October 2019 and updated in March 2022, and references searched from any identified systematic review.Eligibility criteriaStudy inclusion criteria were as follows: (1) original data human research studies, (2) investigated SRC or head impacts, (3) evaluated an SRC prevention intervention, unintended consequence or modifiable risk factor, (4) participants competing in any sport, (5) analytic study design, (6) systematic reviews and meta-analyses were included to identify original data manuscripts in reference search and (7) peer-reviewed. Exclusion criteria were as follows: (1) review articles, pre-experimental, ecological, case series or case studies and (2) not written in English.ResultsIn total, 220 studies were eligible for inclusion and 192 studies were included in the results based on methodological criteria as assessed through the Scottish Intercollegiate Guidelines Network high (‘++’) or acceptable (‘+’) quality. Evidence was available examining protective gear (eg, helmets, headgear, mouthguards) (n=39), policy and rule changes (n=38), training strategies (n=34), SRC management strategies (n=12), unintended consequences (n=5) and modifiable risk factors (n=64). Meta-analyses demonstrated a protective effect of mouthguards in collision sports (incidence rate ratio, IRR 0.74; 95% CI 0.64 to 0.89). Policy disallowing bodychecking in child and adolescent ice hockey was associated with a 58% lower concussion rate compared with bodychecking leagues (IRR 0.42; 95% CI 0.33 to 0.53), and evidence supports no unintended injury consequences of policy disallowing bodychecking. In American football, strategies limiting contact in practices were associated with a 64% lower practice-related concussion rate (IRR 0.36; 95% CI 0.16 to 0.80). Some evidence also supports up to 60% lower concussion rates with implementation of a neuromuscular training warm-up programme in rugby. More research examining potentially modifiable risk factors (eg, neck strength, optimal tackle technique) are needed to inform concussion prevention strategies.ConclusionsPolicy and rule modifications, personal protective equipment, and neuromuscular training strategies may help to prevent SRC.PROSPERO registration numberCRD42019152982.

Musculoskeletal (MSK) injuries and concussions (SRC) are of concern in tackle football, and youth are understudied compared to elite athletes. Policy change is of interest as a means to improve player safety. A reduction in number of players on-field may reduce the number of collisions and subsequently injuries within this population, potentially aiding in future injury prevention strategies.To compare video-suspected (VS) concussion and non-concussion injury rates in a modified 9-on-9 13–15 years old Canadian football season to a traditional 12-on-12 season using video-analysis.Prospective cohortYouth tackle football (Calgary, Canada).Football players aged 13–15 years included 384 players (n=18 teams) participating in 2020 and 500 players (n=12 teams) in 2022. Video data were anonymized.In 2020, in accordance with provincial COVID-19 cohort restrictions, there was a reduction in the number of on-field players (9-on-9) and field-dimensions (150x50 yards). The 2021 season returned to 12-on-12 with field dimensions of 150x65 yards. Independent variables included cohort (9-on-9, 12-on-12) and team unit (offense, defense, kicking team, receiving team). Twenty regular season games (10 in each season) were analyzed.Using previously validated criteria, VS-concussion and non-concussion injuries were identified via Dartfish video software. Using negative binomial regression, VS injury rates (/100 player-plays and/10 gameplay-minutes) and incidence rate ratios (IRR) with 95% confidence intervals were estimated to examine differences between years.In total, 10 VS-concussions and 40 VS non-concussion injuries were identified. No significant differences were identified between 2020 and 2021 seasons for VS concussions [IRRPlays (offense): 0.38; 95% CI: 0.08, 1.85] nor non-concussions [IRRPlays (offense): 0.61; 95% CI: 0.27, 1.38]. No injury or concussion rate differences were identified with a reduced number of players on a smaller field. Future research may benefit from combining video-analysis with injury surveillance and accelerometry data to improve prevention efforts.

ObjectiveTo examine the association between the Mercy Rule (MR) and head impact incidence rates (IR) in Canadian high school football games.DesignCross-sectional video-analysis study.SettingFootball fields (Calgary, Canada).ParticipantsIn 2019, two high-school football teams (ages 15–16) in Calgary, Canada had a total of 16 team-games (N=8 games) videorecorded and analyzed using Dartfish software.Interventions (or Assessment of Risk Factors)As per Football Canada’s Tackle Football Rulebook, the MR (initiates continuous running time) comes into effect when the score differential becomes 35 points or more in the second half of the game.Outcome MeasuresThe outcome measure was head impacts. A negative binomial regression adjusted for cluster by team-game was used to estimate head impact IRs (/team-game and/team-2nd-half) for games with and without the MR in effect. The corresponding incidence rate ratios (IRR) were also estimated.Main ResultsGames with the MR in effect had 28% fewer plays (39% fewer in the 2nd-half) and 27% fewer head impacts per team-game [IR=241.67 (95%CI:199.24, 293.13)] compared with games without [IR=328.91 (95%CI:313.04, 345.57); IRR=0.73 (95% CI:0.61, 0.89)]. In the 2nd-half of games with the MR in effect there were 40% fewer head impacts per team-2nd-half [IR2nd-half=99.16 (95%CI:76.81, 128.03)] compared with games without [IR2nd-half=166.20 (95%CI:156.75, 176.22); IRR2nd-half=0.60 (95%CI:0.47, 0.76].ConclusionsIn this novel evaluation of the Mercy Rule, running time was associated with a 27% lower head impact IR in games (40% in 2nd-half). Consideration for future research should include examining the effect of the MR on concussion IRs.

BackgroundDue to postulated associated long-term health issues in athletes, concussions and head impacts are of concern in tackle football. Football Canada mandated a game clock running-time rule (RTR) in the event of a second-half 35-point difference in games, citing player safety as the main rationale.ObjectiveTo examine the effectiveness of RTR on reducing game-related head impact rates in Canadian high school football using video analysis.DesignCross-sectional.SettingCalgary, Canada.ParticipantsPlayers on two junior division high school teams (ages 15–16) in Calgary, Alberta were included. Fourteen games from the 2019 season (Team A: n=8, Team B: n=6) were videotaped for analyses.Assessment of Risk FactorsTraditionally, the clock stops between plays until the referee signals for the clock to resume. With RTR the clock continues (except during exceptional circumstances such as injury, scores, or timeouts) in the event of a point differential of 35 points or greater in the second half of a game.Main Outcome MeasurementsHead impacts were reported as incidence rates (IR) [# head impacts/100 player-game-minutes (PGM) (95% confidence intervals (95% CI)]. Incidence rate ratios (IRR), offset for PGM, adjusted for game outcome (e.g., win, loss) and clustering by team game were used to compare score differential in games with and without running-time (≥35 points vs. <35 points) by team unit (e.g., offense, defense).ResultsRTR games yielded 24% fewer plays than non-RTR games (IRR: 0.76, 95% CI: 0.68, 0.84). Head impact IR in RTR games were lower than non-RTR games for offensive units (IRR:0.80; 95% CI:0.68, 0.95) and defensive units (IRR:0.76; 95% CI:0.59, 0.99). There were no differences in special teams units.ConclusionsRTR reduced game-related head impact IRs in this cohort for both offensive and defensive units. Sport governing bodies should consider the potential effect of RTR on injury and concussion rates at the youth level.

Objectives The aims were to (1) examine the rates and mechanisms of concussion and head impact in youth football (high school level or younger); (2) identify modifiable risk factors for concussion and head impact; and (3) evaluate the effectiveness of prevention strategies in tackle football at any level. Methods Nine databases (CINAHL Plus with Full Text; Cochrane Central Register of Controlled Trials; EMBASE; ERIC; Ovid MEDLINE(R) and Epub Ahead of Print, In-Process & Other Non-Indexed Citations and Daily; ProQuest Dissertations & Theses Global Database; PsycINFO; Scopus; and SPORTDiscus with Full Text) were searched using the search strategy focusing on four main concepts: concussion/head impact, tackle football, modifiable risk factors, and primary prevention. Two reviewers completed title, abstract, and full-text screening as well as risk of bias assessment (using the Downs and Black checklist), with a third author available to resolve any disagreements. Main Results After removing duplicates, 1911 articles were returned. Fifty-eight articles were included in the review and 20 in the meta-analysis. The overall combined rates of concussion (including game and practice-related concussion) based on the meta-analysis were 0.78 concussions/1000 athlete exposures [95% confidence interval (CI) 0.67–0.89] for high school football (ages 13–19) and 1.15 concussions/1000 athlete exposures (95% CI 0.89–1.41) for minor football players (ages 5–15). There is evidence that contact training and practice contact restrictions have reduced the rate of head impacts and concussion. Heads Up Football (an intervention focused on coach education and contact training) has been shown to reduce the rate of concussion by 32% and head impacts by 38% amongst high school football players. Limiting contact practices in high schools to 2 days per week reduced practice head impacts per player-season by 42%, and limiting full contact in practice to 75 min per week in the second week of the season and 60 min in week 3 and beyond resulted in a 54% decrease in the practice-related concussion rate ( p  = 0.003). Conclusions This review identified a critical need for interventions to address the high rates of concussion and head impact in youth football. To date, contact training and contact restrictions have the strongest evidence supporting their effectiveness at reducing these rates. Future research should use consistent concussion definitions and validated injury surveillance systems, and ensure complete reporting of participant characteristics and sampling details. Prospero ID CRD42020193775.

Sources of infection of most cases of community-acquired Legionnaires' disease (CALD) are unknown. Identification of sources of infection of CALD. Berlin; December 2016-May 2019. Adult cases of CALD reported to district health authorities and consenting to the study; age and hospital matched controls. Percentage of cases of CALD with attributed source of infection. Analysis of secondary patient samples for monoclonal antibody (MAb) type (and sequence type); questionnaire-based interviews, analysis of standard household water samples for Legionella concentration followed by MAb (and sequence) typing of Legionella pneumophila serogroup 1 (Lp1) isolates; among cases taking of additional water samples to identify the infectious source as appropriate; recruitment of control persons for comparison of exposure history and Legionella in standard household water samples. For each case an appraisal matrix was filled in to attribute any of three source types (external (non-residence) source, residential non-drinking water (RnDW) source (not directly from drinking water outlet), residential drinking water (RDW) as source) using three evidence types (microbiological results, cluster evidence, analytical-comparative evidence (using added information from controls)). Inclusion of 111 study cases and 202 controls. Median age of cases was 67 years (range 25-93 years), 74 (67%) were male. Among 65 patients with urine typable for MAb type we found a MAb 3/1-positive strain in all of them. Compared to controls being a case was not associated with a higher Legionella concentration in standard household water samples, however, the presence of a MAb 3/1-positive strain was significantly associated (odds ratio (OR) = 4.9, 95% confidence interval (CI) 1.7 to 11). Thus, a source was attributed by microbiological evidence if it contained a MAb 3/1-positive strain. A source was attributed by cluster evidence if at least two cases were exposed to the same source. Statistically significant general source types were attributed by calculating the population attributable risk (analytical-comparative evidence). We identified an external source in 16 (14%) cases, and RDW as source in 28 (25%). Wearing inadequately disinfected dentures was the only RnDW source significantly associated with cases (OR = 3.2, 95% CI 1.3 to 7.8) and led to an additional 8% of cases with source attribution, for a total of 48% of cases attributed. Using the appraisal matrix we attributed almost half of all cases of CALD to an infectious source, predominantly RDW. Risk for LD seems to be conferred primarily by the type of Legionella rather than the amount. Dentures as a new infectious source needs further, in particular, integrated microbiological, molecular and epidemiological confirmation.

Central abdominal fat is a strong risk factor for diabetes and cardiovascular disease. To identify common variants influencing central abdominal fat, we conducted a two-stage genome-wide association analysis for waist circumference (WC). In total, three loci reached genome-wide significance. In stage 1, 31,373 individuals of Caucasian descent from eight cohort studies confirmed the role of FTO and MC4R and identified one novel locus associated with WC in the neurexin 3 gene [NRXN3 (rs10146997, p = 6.4×10-7)]. The association with NRXN3 was confirmed in stage 2 by combining stage 1 results with those from 38,641 participants in the GIANT consortium (p = 0.009 in GIANT only, p = 5.3×10-8 for combined analysis, n = 70,014). Mean WC increase per copy of the G allele was 0.0498 z-score units (0.65 cm). This SNP was also associated with body mass index (BMI) [p = 7.4×10-6, 0.024 z-score units (0.10 kg/m2) per copy of the G allele] and the risk of obesity (odds ratio 1.13, 95% CI 1.07-1.19; p = 3.2×10-5 per copy of the G allele). The NRXN3 gene has been previously implicated in addiction and reward behavior, lending further evidence that common forms of obesity may be a central nervous system-mediated disorder. Our findings establish that common variants in NRXN3 are associated with WC, BMI, and obesity.

There is a broad class of astrophysical sources that produce detectable, transient, gravitational waves. Some searches for transient gravitational waves are tailored to known features of these sources. Other searches make few assumptions about the sources. Typically events are observable with multiple search techniques. This work describes how to combine the results of searches that are not independent, treating each search as a classifier for a given event. This will be shown to improve the overall sensitivity to gravitational-wave events while directly addressing the problem of consistent interpretation of multiple trials.

We describe a general approach to detection of transient gravitational-wave signals in the presence of non-Gaussian background noise. We prove that under quite general conditions, the ratio of the likelihood of observed data to contain a signal to the likelihood of it being a noise fluctuation provides optimal ranking for the candidate events found in an experiment. The likelihood-ratio ranking allows us to combine different kinds of data into a single analysis. We apply the general framework to the problem of unifying the results of independent experiments and the problem of accounting for non-Gaussian artifacts in the searches for gravitational waves from compact binary coalescence in LIGO data. We show analytically and confirm through simulations that in both cases the likelihood ratio statistic results in an improved analysis.