A Prospective Observational Cohort Comparison of SARS-CoV-2 Seroprevalence Between Paramedics and Matched Blood Donors in Canada During the COVID-19 Pandemic.

STUDY OBJECTIVE: SARS-CoV-2 represents an occupational risk to paramedics, who work in uncontrolled environments. We sought to identify the occupation-specific risk to paramedics by comparing their seroprevalence of SARS-CoV-2 infection-specific antibodies to that of blood donors in Canada. METHODS: In this prospective cohort study, we performed serology testing (Elecsys Anti-SARS-CoV-2 nucleocapsid assay) on samples from paramedics and blood donors (January to July 2021) in Canada. Paramedic samples were compared to blood donor samples through 1:1-matched (based on age, sex, location, date of blood collection, and vaccination status) and raking weighted comparisons. We compared the seroprevalence with a risk difference (and 95% confidence interval [CI]) and performed secondary analyses within subgroups defined by vaccination status. RESULTS: The 1:1 match included 1,627 cases per group; in both groups, 723 (44%) were women, with a median age of 38. The raking weighted comparison included 1,713 paramedic samples and 19,515 blood donor samples, with similar characteristics. In the 1:1 match, the seroprevalence was similar (difference 1.2; 95% CI -0.20 to 2.7) between paramedics (5.2%) and blood donors (3.9%). The raking weighted comparison was consistent (difference 0.97; 95% CI -0.10 to 2.0). The unvaccinated paramedic samples, in comparison to the blood donor samples, demonstrated a higher seroprevalence in the 1:1 (difference 5.9; 95% CI 1.8 to 10) and weighted (difference 6.5; 95% CI 1.8 to 10) comparisons. Among vaccinated cases, the between-group seroprevalence was similar. CONCLUSION: Overall, paramedics demonstrated similar evidence of prior SARS-CoV-2 infection to that of blood donors. However, among unvaccinated individuals, evidence of prior infection was higher among paramedics compared to blood donors.

Low Risk of Wound Complications With Sinus Tarsi Approach for Treatment of Calcaneus Fractures.

BACKGROUND: Operative management displaced intra-articular calcaneus fractures is commonly associated with wound complications. Open reduction internal fixation is traditionally performed through the extensile lateral approach has relatively high rates of wound complications. The sinus tarsi approach to displaced intra-articular calcaneus fractures is a less invasive approach to achieve fracture reduction and fixation as well as reduce wound healing complications. The purpose of this study is to report the rates of wound complications associated with the sinus tarsi approach in the treatment of displaced intra-articular calcaneus fractures. METHODS: We retrospectively identified patients treated with a limited sinus tarsi approach for displaced intra-articular calcaneus fractures from January 2009 to December 2018. Demographic and radiographic data were collected including age, gender, mechanism of injury, occupation, presence of diabetes mellitus, smoking status, Sanders classification, Bohler and Gissane angles. Postoperatively, we recorded the presence of complications, return-to-work time, and radiographic measurements. RESULTS: One hundred and five fractures were identified in 100 patients who underwent open reduction internal fixation for displaced intra-articular calcaneus fractures. Using the Sanders computed tomographic classification, we identified 32% Type 2, 48% Type 3, 18% Type 4, and 2% tongue-type variants. For the preoperative Bohler's angle, 38% of fractures displayed a negative angle, 50% had an angle 0° to 20°, and 12% over 20°. Postoperatively, all patients demonstrated an improvement in Bohler's angle with 13% with 0° to 20° and 87% over 20°. Approximately, 72% of patients working prior to the injury had returned to work by 6 months, and 89% by 12 months. The wound complication rate was 11.9% (12/105), with 1.9% (2/105) requiring additional procedures. There was no significant difference in wound complication rates in smokers versus nonsmokers (11.9% vs 12.2%, p = .55). CONCLUSION: Operative management of displaced intra-articular calcaneus fractures through the sinus tarsi approach allows restoration of calcaneal height with a low rate of wound complications, even among active smokers.

Scaling issues of neutral theory reveal violations of ecological equivalence for dominant Amazonian tree species.

Neutral models are often used as null models, testing the relative importance of niche versus neutral processes in shaping diversity. Most versions, however, focus only on regional scale predictions and neglect local level contributions. Recently, a new formulation of spatial neutral theory was published showing an incompatibility between regional and local scale fits where especially the number of rare species was dramatically under-predicted. Using a forward in time semi-spatially explicit neutral model and a unique large-scale Amazonian tree inventory data set, we show that neutral theory not only underestimates the number of rare species but also fails in predicting the excessive dominance of species on both regional and local levels. We show that although there are clear relationships between species composition, spatial and environmental distances, there is also a clear differentiation between species able to attain dominance with and without restriction to specific habitats. We conclude therefore that the apparent dominance of these species is real, and that their excessive abundance can be attributed to fitness differences in different ways, a clear violation of the ecological equivalence assumption of neutral theory.

Myrcia splendens (Sw.) DC. (syn. M. fallax (Rich.) DC.) (Myrtaceae) Essential Oil from Amazonian Ecuador: A Chemical Characterization and Bioactivity Profile.

In this study, we performed the chemical characterization of Myrcia splendens (Sw.) DC. (Myrtaceae) essential oil from Amazonian Ecuador and the assessment of its bioactivity in terms of cytotoxic, antibacterial, and antioxidant activity as starting point for possible applicative uses. M. splendens essential oil, obtained by hydro-distillation, was analyzed by Gas Chromatography-Mass Spectrometry (GC-MS) and Gas Chromatography-Flame Ionization Detector (GC-FID): the major components were found to be trans-nerolidol (67.81%) and α-bisabolol (17.51%). Furthermore, we assessed the cytotoxic activity against MCF-7 (breast), A549 (lung) human tumor cell lines, and HaCaT (human keratinocytes) non-tumor cell line through 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) test: promising results in terms of selectivity and efficacy against the MCF-7 cell line (IC50 of 5.59 ± 0.13 µg/mL at 48 h) were obtained, mainly due to α-bisabolol. Furthermore, antibacterial activity against Gram positive and negative bacteria were performed through High Performance Thin Layer Chromatography (HPTLC) bioautographic assay and microdilution method: trans-nerolidol and ß-cedren-9-one were the main molecules responsible for the low antibacterial effects against human pathogens. Nevertheless, interesting values of Minimum Inhibitory Concentration (MIC) were noticeable against phytopathogen strains. Radical scavenging activity performed by HPTLC bioautographic and spectrophotometric 1,1-diphenyl-2-picrylhydrazyl (DPPH) approaches were negligible. In conclusion, the essential oil revealed a good potential for plant defense and anti-cancer applications.

Evolutionary heritage influences Amazon tree ecology.

Lineages tend to retain ecological characteristics of their ancestors through time. However, for some traits, selection during evolutionary history may have also played a role in determining trait values. To address the relative importance of these processes requires large-scale quantification of traits and evolutionary relationships among species. The Amazonian tree flora comprises a high diversity of angiosperm lineages and species with widely differing life-history characteristics, providing an excellent system to investigate the combined influences of evolutionary heritage and selection in determining trait variation. We used trait data related to the major axes of life-history variation among tropical trees (e.g. growth and mortality rates) from 577 inventory plots in closed-canopy forest, mapped onto a phylogenetic hypothesis spanning more than 300 genera including all major angiosperm clades to test for evolutionary constraints on traits. We found significant phylogenetic signal (PS) for all traits, consistent with evolutionarily related genera having more similar characteristics than expected by chance. Although there is also evidence for repeated evolution of pioneer and shade tolerant life-history strategies within independent lineages, the existence of significant PS allows clearer predictions of the links between evolutionary diversity, ecosystem function and the response of tropical forests to global change.

Fast demographic traits promote high diversification rates of Amazonian trees.

The Amazon rain forest sustains the world's highest tree diversity, but it remains unclear why some clades of trees are hyperdiverse, whereas others are not. Using dated phylogenies, estimates of current species richness and trait and demographic data from a large network of forest plots, we show that fast demographic traits--short turnover times--are associated with high diversification rates across 51 clades of canopy trees. This relationship is robust to assuming that diversification rates are either constant or decline over time, and occurs in a wide range of Neotropical tree lineages. This finding reveals the crucial role of intrinsic, ecological variation among clades for understanding the origin of the remarkable diversity of Amazonian trees and forests.

Evolution of lifespan.

Present-day evolutionary theory, modern synthesis and evo-devo, appear to explain evolution. There remain however several points of contention. These include: biological time, direction, macroevolution verses microevolution, ageing and the extent of internal as opposed to external mediation. A new theoretical model for the control of biological time in vertebrates/bilaterians is introduced. Rather than biological time being controlled solely by a molecular cascade domino effect, it is suggested there is also an intracellular oscillatory clock. This clock (life's timekeeper) is synchronised across all cells in an organism and runs at a constant frequency throughout life. Slower frequencies extend lifespan, increase body/brain size and advance behaviour. They also create a time void which could aid additional evolutionary change. Faster frequencies shorten lifespan, reduce body/brain size and diminish behaviour. They are therefore less likely to mediate evolution in vertebrates/mammals. It is concluded that in vertebrates, especially mammals, there is a direction in evolution towards longer lifespan/advanced behaviour. Lifespan extension could equate with macroevolution and subsequent modifications with microevolution. As life's timekeeper controls the rate of ageing it constitutes a new genetic theory of ageing. Finally, as lifespan extension is internally mediated, this suggests a major role for internal mediation in evolution.

Markedly divergent estimates of Amazon forest carbon density from ground plots and satellites.

AIM: The accurate mapping of forest carbon stocks is essential for understanding the global carbon cycle, for assessing emissions from deforestation, and for rational land-use planning. Remote sensing (RS) is currently the key tool for this purpose, but RS does not estimate vegetation biomass directly, and thus may miss significant spatial variations in forest structure. We test the stated accuracy of pantropical carbon maps using a large independent field dataset. LOCATION: Tropical forests of the Amazon basin. The permanent archive of the field plot data can be accessed at: http://dx.doi.org/10.5521/FORESTPLOTS.NET/2014_1. METHODS: Two recent pantropical RS maps of vegetation carbon are compared to a unique ground-plot dataset, involving tree measurements in 413 large inventory plots located in nine countries. The RS maps were compared directly to field plots, and kriging of the field data was used to allow area-based comparisons. RESULTS: The two RS carbon maps fail to capture the main gradient in Amazon forest carbon detected using 413 ground plots, from the densely wooded tall forests of the north-east, to the light-wooded, shorter forests of the south-west. The differences between plots and RS maps far exceed the uncertainties given in these studies, with whole regions over- or under-estimated by > 25%, whereas regional uncertainties for the maps were reported to be < 5%. MAIN CONCLUSIONS: Pantropical biomass maps are widely used by governments and by projects aiming to reduce deforestation using carbon offsets, but may have significant regional biases. Carbon-mapping techniques must be revised to account for the known ecological variation in tree wood density and allometry to create maps suitable for carbon accounting. The use of single relationships between tree canopy height and above-ground biomass inevitably yields large, spatially correlated errors. This presents a significant challenge to both the forest conservation and remote sensing communities, because neither wood density nor species assemblages can be reliably mapped from space.

Amanoacondorensis (Phyllanthaceae), a new shrubby species from the Cordillera del Condor in southern Ecuador.

A new species of Amanoa (Phyllanthaceae) is described from the sandstone Nangaritza Plateau in the Cordillera del Cóndor Region in southern Ecuador. Amanoacondorensis J.L.Clark & D.A.Neill is a small tree, 4 m tall that is only known from the type collection. The new species is distinct by a shrub habit, presence of coriaceous leaves with an acuminate apex, and congested inflorescences. The relatively high elevation of the type locality, presence of an androphore, and the habit as shrub or low tree are an unusual combination for Amanoa. The conservation status of A.condorensis is assessed as Critically Endangered (CR), based on IUCN Criteria.

ResumenSe describe una nueva especie de Amanoa (Phyllanthaceae) de la meseta de arenisca de Nangaritza en la región de la Cordillera del Cóndor en el sur de Ecuador. Amanoacondorensis J.L.Clark & D.A.Neill es un pequeño árbol de 4 metros de altura que sólo se conoce de la colección tipo. La nueva especie se distingue por la presencia de inflorescencias congestionadas, hojas coriáceas con ápice acuminado, y porte arbustivo. La elevación relativamente más alta de la localidad tipo, la presencia de un andróforo, y el hábito de arbusto o árbol pequeño son una combinación inusual para Amanoa. El estado de conservación de A.condorensis se evalúa como En Peligro Crítico (CR) según los Criterios de la UICN.

A risk assessment study of SARS-CoV-2 propagation in the manufacturing of cellular products.

The potential infection of cellular therapies by SARS-CoV-2 present high risks, as the target patients for these treatments are often immunocompromised or have chronic diseases associated with a higher risk of serious illness and death by COVID-19. The multicellular tropism of this virus presents challenges for the manufacturing of cell therapies, whereby the material could potentially become infected at the source or during cell processing. In this review we assess the risk of a SARS-CoV-2 propagation in cell types used to date in cellular therapies. Altogether, the risk of SARS-CoV-2 contamination of cellular products remains low. This risk should be evaluated on an individual basis, considering ACE2 and TMPRSS2 expression, existing literature regarding the susceptibility to infection, and single cell RNA sequencing data of COVID-19 patients. This analysis should ideally be performed for both the cells being manufactured and the cells used to produce the vector to ensure patient safety.

Cell therapies are medicines based on the utilization of different cell types that are manufactured in special facilities. SARS-CoV-2, the virus that causes COVID-19, can infect a wide range of cell types. Patients requiring a cell therapy may be at higher risk of severe COVID-19 due to their underlying medical conditions. In this context, it is of importance to evaluate the risk of a SARS-CoV-2 contamination during the production of cell therapies to avoid possible infections. In this review, the authors assess the risk of an infection for cells being used as therapies to date and propose a systematic way to evaluate this risk.

Intramedullary brachytherapy for the treatment of long bone metastatic disease: A case report.

Case: A 56-year-old woman with metastatic melanoma and femoral lesions with impending pathologic fracture was indicated for intramedullary brachytherapy (IMBT) and intramedullary nail. Conclusions: IMBT + intramedullary nail is a new technique for the treatment of long bone metastases. IMBT maximizes radiation to the tumor and minimizes radiation to surrounding tissues. It allows the patient to resume systemic treatment expediently. Our cadaver model and patient were both treated for femoral metastases; however, this technique allows for the treatment of any long bone. This is a safe technique that minimizes treatment time compared with other standard radiation regimens.

Immune profile and mitotic index of metastatic melanoma lesions enhance clinical staging in predicting patient survival.

Although remission rates for metastatic melanoma are generally very poor, some patients can survive for prolonged periods following metastasis. We used gene expression profiling, mitotic index (MI), and quantification of tumor infiltrating leukocytes (TILs) and CD3+ cells in metastatic lesions to search for a molecular basis for this observation and to develop improved methods for predicting patient survival. We identified a group of 266 genes associated with postrecurrence survival. Genes positively associated with survival were predominantly immune response related (e.g., ICOS, CD3d, ZAP70, TRAT1, TARP, GZMK, LCK, CD2, CXCL13, CCL19, CCR7, VCAM1) while genes negatively associated with survival were cell proliferation related (e.g., PDE4D, CDK2, GREF1, NUSAP1, SPC24). Furthermore, any of the 4 parameters (prevalidated gene expression signature, TILs, CD3, and in particular MI) improved the ability of Tumor, Node, Metastasis (TNM) staging to predict postrecurrence survival; MI was the most significant contributor (HR = 2.13, P = 0.0008). An immune response gene expression signature and presence of TILs and CD3+ cells signify immune surveillance as a mechanism for prolonged survival in these patients and indicate improved patient subcategorization beyond current TNM staging.

Pharmacists' views on the impact of the Falsified Medicines Directive on community pharmacies: A cross-sectional survey.

Background: The Falsified Medicines Directive (FMD) was implemented to minimise the circulation of falsified medicines in the legal pharmaceutical supply chain. Whilst pharmacists are involved in the final step of the FMD requirements with the decommissioning of medicines at the point of supply to patients, limited research has been conducted to investigate the impact of fulfilling these requirements on the relevant stakeholders. Objective: To examine community pharmacists' views on how the FMD has affected their practice. Methods: An online survey was disseminated via email in June 2020 to pharmacists in Ireland (n = 4727), who were invited to participate if practising full time or part time in community pharmacies. Quantitative data were captured through multiple option and Likert-scale questions, and analysed using descriptive and inferential statistics. Qualitative data were captured by use of a free-text box, with the open comments analysed thematically. Results: In total, 618 valid responses were received (13.1% response rate). Most perceived that FMD requirements increased waiting times for patients (82%) and reduced time interacting with patients (65%). Only 28% agreed/strongly agreed that the introduction of the FMD legislation improves patient safety. In the open comments, the need for medicine authentication was acknowledged, but it was believed that this should be the wholesalers' responsibility, not pharmacists' responsibility. The additional step of medicines decommissioning was viewed as a time-consuming distraction to clinical checks that increased the risk for error. Pharmacists complained that they were not remunerated for the lost staff productivity or the additional software and equipment costs. Many pharmacists felt that the increased workload was disproportionate to the small risk of patients receiving falsified medicines. Conclusions: Key stakeholder engagement is required to optimise the implementation and integration of the FMD procedures into community pharmacy practice with minimal impact on dispensing and without compromising patient care.

Percutaneous screw fixation of the pubic symphysis versus plate osteosynthesis: a biomechanical study.

Objectives: To compare the stability of screw fixation with that of plate fixation for symphyseal injuries in a vertically unstable pelvic injury (AO/Tile 61-C1) associated with complete disruption of the sacroiliac joint and the pubic symphysis. Methods: Eight fourth-generation composite pelvis models with sacroiliac and pubic symphyseal disruption (Sawbones, Vashon Island, WA) underwent biomechanical testing simulating static single-leg stance. Four were fixed anteriorly with a symphyseal screw, and 4 with a symphyseal plate. All had single transsacral screw fixation posteriorly. Displacement and rotation were monitored at both sacroiliac joint and pubic symphysis. Results: There was no significant difference between the 2 groups for mean maximum force generated. There was no significant difference in net displacement at both sacroiliac joint and pubic symphysis. There was significantly less rotation but more displacement in the screw group in the Z-axis. The screw group showed increased stiffness compared with the plate group. Conclusions: This is the first biomechanical study to compare screw versus plate symphyseal fixation in a Tile C model. Our biomechanical model using anterior and posterior fixation demonstrates that symphyseal screws may be a viable alternative to classically described symphyseal plating.

Biomechanical Comparison of 4 Transsacral Fixation Constructs in a Type 61C, Zone II Pelvic Fracture Model.

OBJECTIVES: OTA/AO 61C pelvic ring injuries are vertically unstable because of complete sacral fractures combined with anterior ring injury. The objective of this study was to compare the biomechanical characteristics of 4 transsacral screw constructs for posterior pelvic ring fixation, including one that uses a novel fixation method with a pair of locked washers with interdigitating cams. METHODS: Type C pelvic ring disruptions were created on 16 synthetic pelvis models. Each pelvis was fixated with an S2 screw in addition to being allocated to 1 of 4 transsacral constructs through S1: (1) 8.0-mm screw, (2) 8.0-mm bolt, (3) 8.0-mm screw locked with a nut, and (4) 8.00-mm screw locked with a nut with the addition of interdigitating washers between the screw head and ilium on the near cortex, and ilium and nut on the far cortex. The anterior ring fractures were not stabilized. Each pelvis underwent 100,000 cycles at 250 N and was then loaded to failure using a unilateral stance testing model. The anterior and posterior osteotomy sites were instrumented with pairs of infrared (IR) light-emitting markers, and the relative displacement of the markers was monitored using a three-dimensional (3D) motion capture system. Displacement measurements at 25,000; 50,000; 75,000; and 100,000 cycles and failure force were recorded for each pelvis. RESULTS: The novel washer design construct performed better than the screw construct with less posterior ring motion at 75,000 ( P = 0.029) and 100,000 cycles ( P = 0.029). CONCLUSIONS: The novel interdigitating washer design may be superior to using a screw construct alone to achieve rigid, locked posterior ring fixation in a synthetic pelvis model with a Type C pelvic ring disruption.

Does Size Matter for Cephalomedullary Nails in Geriatric Intertrochanteric Fractures?

OBJECTIVES: To evaluate the need for reoperation of geriatric intertrochanteric hip fractures treated with 10-mm cephalomedullary nails versus those treated with nails larger than 10 mm. DESIGN: Retrospective review at a single institution. SETTING: Level I trauma center. PATIENTS/PARTICIPANTS: All patients age 60 and over treated with cephalomedullary fixation for an intertrochanteric femur fracture at a single institution. INTERVENTION: Cephalomedullary fixation with variable nail diameters. MAIN OUTCOME MEASUREMENTS: Reoperation rates of geriatric intertrochanteric fractures treated with a size 10-mm diameter cephalomedullary nail compared with patients treated with nails larger than 10 mm. RESULTS: There were no significant differences in reoperation rates when the 10-mm cohort was compared with an aggregate cohort of all nails larger than 10 mm (P = 0.99). This result was true for both all-cause reoperation and noninfectious reoperation. There was no difference between cohorts in regards to age, gender, or fracture pattern. CONCLUSIONS: A 10-mm cephalomedullary nail can be used in lieu of a larger diameter fixation in patients age 60 and older with intertrochanteric femur fractures while still maintaining a comparable rate of reoperation. LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Acute-Phase Reactants in Operatively Treated Upper Extremity Infections: A Retrospective Review.

Background: There are limited data on the use of acute-phase markers in the diagnosis of upper extremity infections. The goal of this study was to determine the percentage of patients with elevated white blood cell (WBC) count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) in the setting of an upper extremity infection requiring operative debridement. Methods: In a retrospective review over 12 years, 61 patients who met the inclusion criteria were identified. Results: C-reactive protein was the most sensitive test in the detection of culture-positive infection compared with ESR and WBC (P < .001, P < .0001, respectively). Ninety percent of patients (55 of 61) presented with an abnormal CRP value. The WBC count and ESR were abnormal in 54% and 67% of our cohort, respectively. Conclusions: C-reactive protein is the most sensitive laboratory test when evaluating upper extremity infections that necessitate debridement. The WBC count and ESR should be interpreted with caution and can be normal even in the presence of an infection.

Real-time PCR detection of Fe-type nitrile hydratase genes from environmental isolates suggests horizontal gene transfer between multiple genera.

Nitriles are widespread in the environment as a result of biological and industrial activity. Nitrile hydratases catalyse the hydration of nitriles to the corresponding amide and are often associated with amidases, which catalyze the conversion of amides to the corresponding acids. Nitrile hydratases have potential as biocatalysts in bioremediation and biotransformation applications, and several successful examples demonstrate the advantages. In this work a real-time PCR assay was designed for the detection of Fe-type nitrile hydratase genes from environmental isolates purified from nitrile-enriched soils and seaweeds. Specific PCR primers were also designed for amplification and sequencing of the genes. Identical or highly homologous nitrile hydratase genes were detected from isolates of numerous genera from geographically diverse sites, as were numerous novel genes. The genes were also detected from isolates of genera not previously reported to harbour nitrile hydratases. The results provide further evidence that many bacteria have acquired the genes via horizontal gene transfer. The real-time PCR assay should prove useful in searching for nitrile hydratases that could have novel substrate specificities and therefore potential in industrial applications.

Dendritic cells and T cells in immunotherapy.

Autologous cellular immunotherapies have been used experimentally in humans to treat many types of cancer. These therapies are divided into two principal types: active cellular immunotherapies that rely on autologous dendritic cells or other antigen presenting cells; and adoptive T-cell therapies, in which large numbers of antigen-specific T lymphocytes are propagated ex vivo and then infused back into the patient. With the FDA approval of the antigen presenting cell vaccine sipuleucel-T for prostate cancer, active immunization has become an accepted approach for the treatment of established cancer.

Competition influences tree growth, but not mortality, across environmental gradients in Amazonia and tropical Africa.

Competition among trees is an important driver of community structure and dynamics in tropical forests. Neighboring trees may impact an individual tree's growth rate and probability of mortality, but large-scale geographic and environmental variation in these competitive effects has yet to be evaluated across the tropical forest biome. We quantified effects of competition on tree-level basal area growth and mortality for trees ≥10-cm diameter across 151 ~1-ha plots in mature tropical forests in Amazonia and tropical Africa by developing nonlinear models that accounted for wood density, tree size, and neighborhood crowding. Using these models, we assessed how water availability (i.e., climatic water deficit) and soil fertility influenced the predicted plot-level strength of competition (i.e., the extent to which growth is reduced, or mortality is increased, by competition across all individual trees). On both continents, tree basal area growth decreased with wood density and increased with tree size. Growth decreased with neighborhood crowding, which suggests that competition is important. Tree mortality decreased with wood density and generally increased with tree size, but was apparently unaffected by neighborhood crowding. Across plots, variation in the plot-level strength of competition was most strongly related to plot basal area (i.e., the sum of the basal area of all trees in a plot), with greater reductions in growth occurring in forests with high basal area, but in Amazonia, the strength of competition also varied with plot-level wood density. In Amazonia, the strength of competition increased with water availability because of the greater basal area of wetter forests, but was only weakly related to soil fertility. In Africa, competition was weakly related to soil fertility and invariant across the shorter water availability gradient. Overall, our results suggest that competition influences the structure and dynamics of tropical forests primarily through effects on individual tree growth rather than mortality and that the strength of competition largely depends on environment-mediated variation in basal area.