Race and Sex Disparities in Lower Extremity Total Joint Arthroplasty: A Retrospective Database Study.

INTRODUCTION: Total joint arthroplasty (TJA) is successful in improving health-related quality of life. However, outcomes vary in the literature due to modifiable and non-modifiable factors. Modifiable factors consist of body mass index (BMI), nutrition, and tobacco use. Non-modifiable risk factors include age, race, sex, and socioeconomic status. Prior literature has focused on racial disparities in terms of the utilization of lower extremity arthroplasty. The purpose of this study is to determine the effect of race and sex on the in-hospital complication rate, length of stay, and charges associated with primary TJA. METHODS: This retrospective cohort utilized complex survey data from the National Inpatient Sample (NIS) between 2016 and 2019. The use of the International Classification of Disease-10 Procedure Codes (ICD-10 PCS) for right hip, left hip, right knee, and left knee TJA yielded a preliminary total of 2,660,280 patients. The exclusion criteria were bilateral arthroplasty and concomitant unilateral hip and knee arthritis. Major complications were defined as acute myocardial infarction, cardiac arrest, pulmonary embolism, adult respiratory distress syndrome, stroke, shock, and septicemia. Odds ratio (OR) and beta coefficients were adjusted for age, sex, primary payer, hospital region, hospital teaching status, and year. Total charges were adjusted for inflation using the Consumer Price Index data reported by the US Bureau of Labor Statistics. RESULTS: A total of 2,589,510 patients met our inclusion criteria; 87.6%, 5.9%, 4.8%, 1.4%, and 0.3% of people were 'White', 'Black', 'Hispanic', 'Asian, or Pacific Islander', and 'Native American', as defined by the National (Nationwide) Inpatient Sample (NIS) Variable 'RACE'. Black individuals experienced a significantly greater major complication rate compared to White individuals (0.87% vs. 0.74%, OR 1.25, p-value = 0.0004). Black and Hispanic individuals experienced a significantly greater minor complication rate compared to White individuals (6.39% vs. 4.12%, odds ratio (OR) 1.61, p-value < 0.0001; 4.68% vs. 4.12%, OR 1.17, p-value < 0.0001). Black, Hispanic, Asian or Pacific Islander, and Native American individuals stayed, on average, 0.33, 0.19, 0.19, and 0.25 days longer than White individuals (2.78, 2.54, 2.55, 2.56 vs. 2.37 days, p<0.0001). None of these statistically significant differences exceeded the established minimal clinically important difference of two days. Black, Hispanic, and Asian or Pacific Islander patients were charged $5,751, $18,656, and $12,119 more than White patients ($72,122, $85,027, $78,490, and $59,297 vs. $66,371, p ≤ 0.0165). Native American patients were charged $7,074 less than White patients ($59,297 vs. $66,371, p < 0.0001). CONCLUSIONS: Black and Hispanic TJA patients may have higher complication rates than White TJA patients. The differences in length of stay between race groups may not affect outcomes. Hispanic patients received significantly more charges than White patients, and Native American patients received significantly fewer charges than White patients after controlling for non-modifiable risk factors. Addressing the charge disparities may reduce the total national cost burden associated with TJA. The present study highlights the need for further studies on healthcare outcomes related to race and sex.

Climate change affects bird nesting phenology: Comparing contemporary field and historical museum nesting records.

Global climate change impacts species and ecosystems in potentially harmful ways. For migratory bird species, earlier spring warm-up could lead to a mismatch between nesting activities and food availability. CO2 provides a useful proxy for temperature and an environmental indicator of climate change when temperature data are not available for an entire time series. Our objectives were to (a) examine nesting phenology over time; (b) determine how nesting phenology relates to changes in atmospheric CO2 concentration; and (c) demonstrate the usefulness of historical museum collections combined with modern observations for trend analyses. We assessed changes in nesting dates of 72 bird species in the Upper Midwest of the United States by comparing contemporary lay dates with those obtained from archived, historical museum nest records over a 143-year period (1872-2015). Species-specific changes in lay date per one unit change in the CO2 residual ranged from -0.75 (95% CI: -1.57 to -0.10) to 0.45 (95% CI: -0.29 to 1.43). Overall, lay dates advanced ~10 days over the 143-year period. Resident, short-distance migrants and long-distance migrants lay dates advanced by ~15, 18 and 16 days on average respectively. Twenty-four species (33.3%) significantly advanced, one (1.4%) significantly delayed and we failed to detect an advance or delay in lay date for 47 species (65.3%). Overall mean advance in first lay date (for the species that have significantly advanced laying date) was 25.1 days (min: 10.7, max: 49.9). Our study highlights the scientific importance of both data gathering and archiving through time to understand phenological change. The detailed archived information reported by egg collectors provide the early data of our study. As with studies of egg-shell thinning and pesticide exposure, our use of these data illustrates another scientific utility of egg collections that these pioneer naturalists never imagined. As museums archive historical data, these locations are also ideal candidates to store contemporary field data as it is collected. Together, such information will provide the ability to track, understand and perhaps predict responses to human-driven environmental change.

Current applications of gait analysis after total knee arthroplasty: A scoping review.

Introduction: The biomechanics of the knee do not return to normal after knee replacement. The purpose of this scoping review is to summarize the current use of gait analysis in total knee arthroplasty and to identify the preoperative motion analysis parameters for which a systematic review aimed at determining the reliability and validity may be warranted. Materials and methods: This IRB-exempt scoping review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) checklist. The 279 articles from the five search engines underwent a title/abstract and full-text screening. Included articles were categorized as either: the role of gait analysis as a research tool for operative decisions, other research applications for motion analysis in total knee arthroplasty, gait analysis as a tool in predicting radiologic outcomes, or gait analysis as a tool in predicting clinical outcomes. Results: Eleven articles studied gait analysis as a research tool in studying operative decisions. Five articles studied other research applications for motion analysis in total knee arthroplasty. Other research applications for motion analysis currently include studying the role of the unicompartmental knee arthroplasty and novel physical therapy protocols aimed at optimizing post-operative care. Two articles studied motion analysis as a tool for predicting radiographic outcomes. 15 articles studied motion analysis in conjunction with clinical scores. Conclusions: There is a broad range of research applications for motion analysis in knee reconstruction. Current limitations include vague definitions of 'gait analysis' or 'motion analysis' and a limited number of articles with preoperative and postoperative outcomes. Knee adduction moment, knee adduction impulse, total knee range of motion, varus angle, cadence, stride length, and velocity have the potential for integration into composite clinical scores. A systematic review to determine the psychometric properties of these variables is warranted.

Characterization of the Mucosally-Adherent Duodenal Microbiome in Children with and without Crohn's Disease.

Manipulation of the microbiome is a rational treatment strategy for inflammatory bowel disease (IBD). Compared to the colon and terminal ileum (TI), understanding of the microbial composition in the duodenum is sparse. This gap in knowledge is especially significant for children with Crohn's disease (CD) because the prevalence of duodenal CD is higher in children than in adults. Our aim was to characterize the bacterial composition of the mucosally-adherent duodenal microbiome in children with and without CD as a first step toward development of targeted IBD treatment strategies at this disease location. Fresh-frozen mucosal biopsies were obtained from the duodenum and TI of children with treatment-naïve CD and age- and sex-matched controls. Extracted DNA was analyzed for sequence variation in the 16S ribosomal RNA bacterial gene region V4 (Novogene; Beijing, China). Bacterial relative abundance, alpha and beta composition, and diversity, were compared across duodenal and TI samples from the controls and CD groups with and without chronic active inflammation (118 samples from 73 children total; approx. 50% CD), using UniFrac dissimilarity coefficients (α < 0.05), Linear Discriminant Analysis Effect Size (LEfSe) analysis (LDA score ≥ 2), and Unweighted Pair Group Method with Arithmetic Mean (UPGMA) analysis. The relationships between bacterial abundance, sex, age, concomitant medication use, and villous length were assessed. The microbial composition in the duodenum was significantly different from the TI in the control population(R-value = 0.558, p = 0.001) and in children with active CD (R-value = 0.301, p = 0.001). Significant differences in bacterial abundance were noted between the control and CD duodena (LDA > 4). The duodenum of children without CD was characterized by increased abundance in Pseudomonodales, whereas the actively inflamed duodenum in CD was characterized by increased abundance of Bacteroidales, specifically the family Prevotellaceae. This trend is opposite of previously published observations of microbial composition in the TI, where active inflammation was associated with a relative decrease in the abundance of Bacteroidetes and an increase in Proteobacteria, including Pseudomonadales. No statistically significant correlations were noted between abundance and age, sex, concomitant medication use or villous length, except for Bacteroidetes, which significantly decreased in abundance in the TI with age (p = 0.048). The pediatric duodenal microbiome is distinct from the TI and characterized by an increased abundance of Pseudomonodales and Spirochetes in healthy children, and an increased abundance of Bacteroidales in active CD patients.

Self-Reported Metal Allergy and Early Outcomes After Total Knee Arthroplasty.

The impact of self-reported metal allergy (SRMA) in total knee arthroplasty (TKA) remains controversial. In the absence of objective tests, SRMA is often used as a screening tool for implant selection. The objective of this study was to determine the effect of SRMA on early outcomes after TKA. Between 2010 and 2014, 168 patients with SRMA underwent TKA; 150 (89%) received nickel-free implants, and 18 (11%) received cobalt-chrome implants that contained nickel. Mean age was 67 years, and 95% were female. A cohort of 858 TKA patients (mean age, 68 years) without SRMA matched by sex served as the control group. Outcomes included Knee Society Score (function [KSS-F] and knee [KSS-K]), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores, knee flexion, further surgery, and complications. No differences were seen in KSS-F and KSS-K between patients with and without SRMA. The mean WOMAC pain scores were 89.1 for patients with SRMA and 85.2 for patients without SRMA (P=.030). Stiffness and physical function scores were similar. Knee flexion was similar. No differences were found between nickel-free and cobalt-chrome SRMA groups. Patients with SRMA and those without demonstrated similar early functional outcomes. Patients with SRMA who received standard cobalt-chrome implants had no significant difference in functional outcomes compared with patients with nickel-free implants. Better identifiers of patients at risk for adverse events due to implant material are needed. [Orthopedics. 2019; 42(6):330-334.].

Anemia in Pediatric Inflammatory Bowel Disease.

OBJECTIVES: Anemia is the most frequent extra-intestinal finding in inflammatory bowel disease (IBD). The aim of this study is to determine the prevalence and types of anemia in pediatric patients with IBD at diagnosis and at approximately 1 year follow-up. METHODS: This is a retrospective chart review of patients diagnosed with IBD from 2005 to 2012, ages 1 to 18 years. Patients who had hemoglobin, hematocrit, mean corpuscular volume, and iron indices obtained at the time of diagnosis and at approximately 1 year follow-up were included in the study. The prevalence of anemia at the beginning and the end of the study was recorded. Using the soluble transferrin receptor index the type of anemia was determined. RESULTS: At diagnosis, 67.31% of patients were anemic. Overall, 28.85% of patients had either iron deficiency anemia (IDA) or a combination of IDA and anemia of chronic disease (ACD), whereas 38.46% had ACD alone. At follow-up, 20.51% were anemic. 15.38% had either IDA or a combination of IDA and ACD; 5.13% had ACD alone. The pattern of anemia and response to therapy differed among the IBD phenotypes CONCLUSIONS:: Anemia is frequent in inflammatory bowel disease. The prevalence was higher in Crohn disease (CD). At 1 year, the prevalence of anemia decreased significantly, but persisted. Anemia of chronic disease predominated in CD. Iron deficiency anemia continued to be present in CD and ulcerative colitis.

Chlorhexidine Antiseptic Irrigation Eradicates Staphylococcus epidermidis From Biofilm: An In Vitro Study.

BACKGROUND: Antiseptic and antibacterial solutions used for intraoperative irrigation are intended to kill bacteria and thereby decrease the incidence of surgical site infections. It is unknown if the concentrations and exposure times of irrigation solutions commonly used for prophylaxis in clean cases (povidone-iodine 0.35% for 3 minutes) are effective against bacteria in biofilm that are present in implant infections. Currently, povidone-iodine (0.35%), chlorhexidine (0.05%), sodium hypochlorite (0.125%), and triple antibacterial solution are all being used off-label for wound irrigation after surgical débridement for orthopaedic infections. QUESTIONS/PURPOSES: Do commonly used antibacterials and antiseptics kill bacteria in established biofilm at clinically relevant concentrations and exposure times? METHODS: Staphylococcus epidermidis (ATCC#35984) biofilms were exposed to chlorhexidine (0.025%, 0.05%, and 0.1%), povidone-iodine (0.35%, 1.0%, 3.5%, and 10%), sodium hypochlorite (0.125%, 0.25%, and 0.5%,), and triple antibacterial solution (bacitracin 50,000 U/L, gentamicin 80 mg/L, and polymyxin 500,000 U/L) for 1, 5, and 10 minutes in triplicate. Surviving bacteria were detected by 21-day subculture. Failure to eradicate all bacteria in any of the three replicates was considered to be "not effective" for that respective solution, concentration, and exposure time. RESULTS: Chlorhexidine 0.05% and 0.1% at all three exposure times, povidone-iodine 10% at all three exposure times, and povidone-iodine 3.5% at 10 minutes only were effective at eradicating S epidermidis from biofilm. All concentrations and all exposure times of sodium hypochlorite and triple antibacterial solution were not effective. CONCLUSIONS: Chlorhexidine is capable of eradicating S epidermidis from biofilm in vitro in clinically relevant concentrations and exposure times. Povidone-iodine at commonly used concentrations and exposure times, sodium hypochlorite, and triple antibacterial solutions are not. CLINICAL RELEVANCE: This in vitro study suggests that chlorhexidine may be a more effective irrigation solution for S epidermidis in biofilm than other commonly used solutions, such as povidone-iodine, Dakin's solution, and triple antibiotic solution. Clinical outcomes should be studied to determine the most effective antiseptic agent, concentration, and exposure time when intraoperative irrigation is used in the presence of biofilm.

Fresh Osteochondral Allograft Transplantation: Is Graft Storage Time Associated With Clinical Outcomes and Graft Survivorship?

BACKGROUND: Regulatory concerns and the popularity of fresh osteochondral allograft (OCA) transplantation have led to a need for prolonged viable storage of osteochondral grafts. Tissue culture media allow a longer storage time but lead to chondrocyte death within the tissue. The long-term clinical consequence of prolonged storage is unknown. HYPOTHESIS: Patients transplanted with OCAs with a shorter storage time would have lower failure rates and better clinical outcomes than those transplanted with OCAs with prolonged storage. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: A matched-pair study was performed of 75 patients who received early release grafts (mean storage, 6.3 days [range, 1-14 days]) between 1997 and 2002, matched 1:1 by age, diagnosis, and graft size, with 75 patients who received late release grafts (mean storage time, 20.0 days [range, 16-28 days]) from 2002 to 2008. The mean age was 33.5 years, and the median graft size was 6.3 cm2. All patients had a minimum 2-year follow-up. Evaluations included pain, satisfaction, function, failures, and reoperations. Outcome measures included the modified Merle d'Aubigné-Postel (18-point) scale, International Knee Documentation Committee (IKDC) form, and Knee Society function (KS-F) scale. Clinical failure was defined as revision OCA transplantation or conversion to arthroplasty. RESULTS: Among patients with grafts remaining in situ, the mean follow-up was 11.9 years (range, 2.0-16.8 years) and 7.8 years (range, 2.3-11.1 years) for the early and late release groups, respectively. OCA failure occurred in 25.3% (19/75) of patients in the early release group and 12.0% (9/75) of patients in the late release group ( P = .036). The median time to failure was 3.5 years (range, 1.7-13.8 years) and 2.7 years (range, 0.3-11.1 years) for the early and late release groups, respectively. The 5-year survivorship of OCAs was 85% for the early release group and 90% for the late release group ( P = .321). No differences in postoperative pain and function were noted between the groups. Ninety-one percent of the early release group and 93% of the late release group reported satisfaction with OCA results. CONCLUSION: The transplantation of OCA tissue with prolonged storage is safe and effective for large osteochondral lesions of the knee and has similar clinical outcomes and satisfaction to the transplantation of early release grafts.

Information-Mediated Allee Effects in Breeding Habitat Selection.

Social information is used widely in breeding habitat selection and provides an efficient means for individuals to select habitat, but the population-level consequences of this process are not well explored. At low population densities, efficiencies may be reduced because there are insufficient information providers to cue high-quality habitat. This constitutes what we call an information-mediated Allee effect. We present the first general model for an information-mediated Allee effect applied to breeding habitat selection and unify personal and social information, Allee effects, and ecological traps into a common framework. In a second model, we consider an explicit mechanism of social information gathering through prospecting on conspecific breeding performance. In each model, we independently vary personal and social information use to demonstrate how dependency on social information may result in either weak or strong Allee effects that, in turn, affect population extinction risk. Abrupt transitions between outcomes can occur through reduced information transfer or small changes in habitat composition. Overall, information-mediated Allee effects may produce positive feedbacks that amplify population declines in species that are already experiencing environmentally driven stressors, such as habitat loss and degradation. Alternatively, social information has the capacity to rescue populations from ecological traps.

Two novel vocalizations are used by veeries (Catharus fuscescens) during agonistic interactions.

Avian vocalizations are common examples of the complex signals used by animals to negotiate during agonistic interactions. In this study, we used two playback experiments to identify agonistic signals in a songbird species with several acoustically complex songs and calls, the veery. In the first experiment, we compared veery singing behavior in response to simulated territorial intrusions including playback of three variations of veery song: 1) song alone as a control, 2) songs with added whisper calls, and 3) songs with introductory notes removed. In the second experiment, we used multimodal stimuli including songs, whisper calls and songs with introductory notes removed, along with a robotic veery mount. Focal males readily responded to all of the playback stimuli, approached the speaker and/or robotic mount, and vocalized. Male veeries gave more whisper calls, and sang more songs without the introductory note in response to all types of playback. However, veeries responded similarly to all types of stimuli presented, and they failed to physically attack the robotic mount. These results indicate that rival veeries use two different types of novel vocalizations: whisper calls and songs lacking the introductory note as agonistic signals, but do not allow us to discern the specific functions of these two vocalizations.

Co-infection of blacklegged ticks with Babesia microti and Borrelia burgdorferi is higher than expected and acquired from small mammal hosts.

Humans in the northeastern and midwestern United States are at increasing risk of acquiring tickborne diseases--not only Lyme disease, but also two emerging diseases, human granulocytic anaplasmosis and human babesiosis. Co-infection with two or more of these pathogens can increase the severity of health impacts. The risk of co-infection is intensified by the ecology of these three diseases because all three pathogens (Borrelia burgdorferi, Anaplasma phagocytophilum, and Babesia microti) are transmitted by the same vector, blacklegged ticks (Ixodes scapularis), and are carried by many of the same reservoir hosts. The risk of exposure to multiple pathogens from a single tick bite and the sources of co-infected ticks are not well understood. In this study, we quantify the risk of co-infection by measuring infection prevalence in 4,368 questing nymphs throughout an endemic region for all three diseases (Dutchess County, NY) to determine if co-infections occur at frequencies other than predicted by independent assortment of pathogens. Further, we identify sources of co-infection by quantifying rates of co-infection on 3,275 larval ticks fed on known hosts. We find significant deviations of levels of co-infection in questing nymphs, most notably 83% more co-infection with Babesia microti and Borrelia burgdorferi than predicted by chance alone. Further, this pattern of increased co-infection was observed in larval ticks that fed on small mammal hosts, but not on meso-mammal, sciurid, or avian hosts. Co-infections involving A. phagocytophilum were less common, and fewer co-infections of A. phagocytophilum and B. microti than predicted by chance were observed in both questing nymphs and larvae fed on small mammals. Medical practitioners should be aware of the elevated risk of B. microti/B. burgdorferi co-infection.

Prevalence of human-active and variant 1 strains of the tick-borne pathogen Anaplasma phagocytophilum in hosts and forests of eastern North America.

Anaplasmosis is an emerging infectious disease caused by infection with the bacterium Anaplasma phagocytophilum. In the eastern United States, A. phagocytophilum is transmitted to hosts through the bite of the blacklegged tick, Ixodes scapularis. We determined the realized reservoir competence of 14 species of common vertebrate hosts for ticks by establishing the probability that each species transmits two important strains of A. phagocytophilum (A. phagocytophilum human-active, which causes human cases, and A. phagocytophilum variant 1, which does not) to feeding larval ticks. We also sampled questing nymphal ticks from ∼ 150 sites in a single county over 2 years and sampled over 6 years at one location. White-footed mice (Peromyscus leucopus) and Eastern chipmunks (Tamias striatus) were the most competent reservoirs for infection with the A. phagocytophilum human-active strain. Across the county, prevalence in ticks for both strains together was 8.3%; ticks were more than two times as likely to be infected with A. phagocytophilum human-active as A. phagocytophilum variant 1.

Distribution of molecules locally delivered from bone cement.

Revision of infected orthopedic implants is successful in most cases when antimicrobials are delivered locally (mixed with bone cement or bone graft which is placed in the site from which the infected tissue was removed); however, there is still a substantial rate of recurrence most likely due to the antimicrobials not achieving a therapeutic dose at all locations in the tissue. To study transport within this environment, gadolinium chelated in diethylene triamine pentaacetic acid (Gd-DTPA), a MRI contrast agent with size and solubility similar to two common antimicrobials (gentamicin and vancomycin), was mixed with bone cement, implanted in vivo into two models of orthopedic surgical wounds, and imaged using MRI 5.5 h after implantation. Image thresholding was used to create two-dimensional and three-dimensional representations of areas/volumes containing detectable concentrations of Gd-DTPA. Distribution is found to be anisotropic with Gd-DTPA transporting preferentially anterior of the implant toward the skin. When fascia is not closed over the implant site, Gd-DTPA transports to the skin and along the subcutaneous plane. The distance transported indicates that transport is likely driven by convection. Finally, the tissue concentration of Gd-DTPA is much less than the concentration loaded into the bone cement.

Effect of body mass index on limb alignment after total knee arthroplasty.

Prior studies have reported increased failure rates in obese patients with postoperative limb mal-alignment. This study was undertaken to determine if a relationship exists between postoperative limb alignment and BMI in patients undergoing primary TKA performed with mechanical instruments. An IRB-approved retrospective review of 196 knees was undertaken. Limb alignment was determined on full-length, standing, hip-to-ankle x-rays, preoperatively and postoperatively. The effects of gender, side, preoperative mechanical alignment and BMI on postoperative alignment were analyzed via multivariate regression analysis. Both preoperative mechanical limb alignment (P<0.001) and BMI (P=0.009) had a significant effect on postoperative limb alignment following TKA performed with mechanical instruments.

Voriconazole is cytotoxic at locally delivered concentrations: a pilot study.

BACKGROUND: Fungal infections are rare but major problems when they involve orthopaedic implants. Preferred treatment in North America is two-staged: resection and then delayed reconstruction, with local delivery of an antifungal between stages. The effect of voriconazole, a hydrophobic antifungal, on local tissues and wound healing is unclear. QUESTIONS/PURPOSES: We asked: (1) Is voriconazole cytotoxic to fibroblasts or osteoblasts at target concentrations for local delivery? And (2) if cytotoxic, can fibroblasts or osteoblasts resume proliferation after voriconazole is removed? METHODS: We exposed 5000 fibroblasts or osteoblasts/well to voriconazole concentrations of 0, 1, 5, 10, 25, 100, 500, 1000, 5000, 10,000, and 20,000 µg/mL (n=4 wells/concentration) in 24-well plates. At 3 and 7 days, cell growth was assessed with alamarBlue® and light microscopy. After Day 7, exposure to voriconazole was stopped and incubation continued for 4 days in medium with no voriconazole. On Day 11, cell growth (recovery) was assessed with alamarBlue® and light microscopy. RESULTS: Increasing voriconazole concentration to more than 100 µg/mL decreased osteoblast and fibroblast growth. Cell growth recovered after 7 days' exposure to 1000 µg/mL or less. CONCLUSIONS: Voriconazole is cytotoxic to osteoblasts and fibroblasts, but cell growth recovers over 4 days after exposure to 1000 µg/mL or less. CLINICAL RELEVANCE: Cytotoxicity seen from voriconazole to mouse osteoblasts and fibroblasts occurs at concentrations achievable clinically from local delivery. It may be prudent to limit the dose of voriconazole in antibiotic-loaded bone cement.

Reservoir competence of vertebrate hosts for Anaplasma phagocytophilum.

Fourteen vertebrate species (10 mammals and 4 birds) were assessed for their ability to transmit Anaplasma phagocytophilum, the bacterium that causes human granulocytic anaplasmosis, to uninfected feeding ixodid ticks. Small mammals were most likely to infect ticks but all species assessed were capable of transmitting the bacterium, in contrast to previous findings.

Scale-dependent neighborhood effects: shared doom and associational refuge.

A resource's susceptibility to predation may be influenced by its own palatability and the palatability of its neighbors. We tested for effects of plant chemical defenses on seed survival by manipulating the frequency of palatable and less palatable sunflower seeds in food patches subject to harvest by fox squirrels (Sciurus niger) and gray squirrels (Sciurus carolinensis). We varied resource distributions at three scales: among stations (aggregates of patches ca. 50 m apart), among patches immediately adjacent to each other, and within patches. When food patches were segregated into high-palatability and low-palatability stations (Experiment 1), seeds suffered greater mortality at stations with high levels of palatable seeds. In the same experiment, within patches, squirrels selected strongly for palatable seeds over less palatable seeds. When high- and low-palatability food patches were placed together at the same stations (Experiment 2), increasing densities of co-occurring palatable seeds amplified the mortality of less palatable seeds, indicating "shared doom." When palatable and less palatable seeds were partitioned into micropatches (Experiment 3), associational effects disappeared, as predicted. Furthermore, selectivity in less palatable patches increased as the initial densities of palatable seeds increased, and selectivity in palatable patches decreased as the initial densities of less palatable seeds increased. Foraging theory predicts associational effects among prey that vary in palatability. Our results show how the type and magnitude of associational effects emerge from the interplay among the spatial scale of prey heterogeneity, the diet selection strategy, and the scale-dependent foraging responses of the consumer.

Nesting songbirds assess spatial heterogeneity of predatory chipmunks by eavesdropping on their vocalizations.

1. Information benefits organisms living in a heterogeneous world by reducing uncertainty associated with decision making. For breeding passerines, information reliably associated with nest failure, such as predator activity, can be used to adjust breeding decisions leading to higher reproductive success. 2. Predator vocalizations may provide a source of current information for songbirds to assess spatial heterogeneity in risk that enables them to make appropriate nest-site and territory placement decisions. 3. To determine whether ground-nesting passerines eavesdrop on a common nest predator, the eastern chipmunk (Tamias striatus), we conducted a playback experiment to create spatial heterogeneity in perceived predation risk. We established three types of playback plots broadcasting: (i) chipmunk vocalizations (increased risk), (ii) frog calls (procedural control) and (iii) no playback (silent control). We conducted point counts from plot centres to compare bird activity among treatments and measured the distance of two ground-nesting species' nests, ovenbird (Seiurus aurocapilla) and veery (Catharus fuscescens), from playback stations. 4. Ground-nesting birds significantly reduced their activities up to 30 m from plot centres in response to playbacks of chipmunk calls suggesting an adjustment of territory placement or a reduction of overt behaviours (e.g. singing frequency). In contrast, less vulnerable canopy-nesting species showed no effect across experimental plots. Correspondingly, veeries and ovenbirds nested significantly further from chipmunk playback stations relative to control stations. Interestingly, the magnitude of this response was more than twice as high in ovenbirds than in veeries. 5. Our findings indicate that some breeding passerines may eavesdrop on predator communication, providing an explanation for how some birds assess spatial heterogeneity in predation risk to make breeding site decisions. Thus, heterospecific eavesdropping may be a common feature of predator-prey interactions that allows birds to avoid nest predators in space and provide greater stability to predator-prey dynamics.

Impact of host community composition on Lyme disease risk.

The drivers of variable disease risk in complex multi-host disease systems have proved very difficult to identify. Here we test a model that explains the entomological risk of Lyme disease (LD) in terms of host community composition. The model was parameterized in a continuous forest tract at the Cary Institute of Ecosystem Studies (formerly the Institute of Ecosystem Studies) in New York State, U.S.A. We report the results of continuing longitudinal observations (10 years) at the Cary Institute, and of a shorter-term study conducted in forest fragments in LD endemic areas of Connecticut, New Jersey, and New York, USA. Model predictions were significantly correlated with the observed nymphal infection prevalence (NIP) in both studies, although the relationship was stronger in the longer-term Cary Institute study. Species richness was negatively, albeit weakly, correlated with NIP (logistic regression), and there was no relationship between the Shannon diversity index (H') and NIP. Although these results suggest that LD risk is in fact dependent on host diversity, the relationship relies explicitly on the identities and frequencies of host species such that conventional uses of the term biodiversity (i.e., richness, evenness, H') are less appropriate than are metrics that include species identity. This underscores the importance of constructing interaction webs for vertebrates and exploring the direct and indirect effects of anthropogenic stressors on host community composition.