Akaike's information criterion in generalized estimating equations

Complexities of short-term mobility for sex work and migration among sex workers: violence and sexual risks, barriers to care, and enhanced social and economic opportunities

Despite research on the health and safety of mobile and migrant populations in the formal and informal sectors globally, limited information is available regarding the working conditions, health, and safety of sex workers who engage in short-term mobility and migration. The objective of this study was to longitudinally examine work environment, health, and safety experiences linked to short-term mobility/migration (i.e., worked or lived in another city, province, or country) among sex workers in Vancouver, Canada, over a 2.5-year study period (2010-2012). We examined longitudinal correlates of short-term mobility/migration (i.e., worked or lived in another city, province, or country over the 3-year follow-up period) among 646 street and off-street sex workers in a longitudinal community-based study (AESHA). Of 646 sex workers, 10.84 % (n = 70) worked or lived in another city, province, or country during the study. In a multivariate generalized estimating equations (GEE) model, short-term mobility/migration was independently correlated with older age (adjusted odds ratio (AOR) 0.95, 95 % confidence interval (CI) 0.92-0.98), soliciting clients in indoor (in-call) establishments (AOR 2.25, 95 % CI 1.27-3.96), intimate partner condom refusal (AOR 3.00, 1.02-8.84), and barriers to health care (AOR 1.77, 95 % CI 1.08-2.89). In a second multivariate GEE model, short-term mobility for sex work (i.e., worked in another city, province, or country) was correlated with client physical/sexual violence (AOR 1.92, 95 % CI 1.02-3.61). In this study, mobile/migrant sex workers were more likely to be younger, work in indoor sex work establishments, and earn higher income, suggesting that short-term mobility for sex work and migration increase social and economic opportunities. However, mobility and migration also correlated with reduced control over sexual negotiation with intimate partners and reduced health care access, and mobility for sex work was associated with enhanced workplace sexual/physical violence, suggesting that mobility/migration may confer risks through less control over work environment and isolation from health services. Structural and community-led interventions, including policy support to allow for more formal organizing of sex work collectives and access to workplace safety standards, remain critical to supporting health, safety, and access to care for mobile and migrant sex workers.

Bidirectional Syntactic Priming across Cognitive Domains: From Arithmetic to Language and Back

Scheepers et al. [Scheepers, C., Sturt, P., Martin, C. J., Myachykov, A., Teevan, K., & Viskupova, I. (2011). Structural priming across cognitive domains: From simple arithmetic to relative clause attachment. Psychological Science, 22, 1319–1326. doi:10.1177/0956797611416997] showed that the structure of a correctly solved mathematical equation affects how people subsequently complete sentences containing high versus low relative-clause attachment ambiguities. Here we investigated whether such effects generalize to different structures and tasks and, importantly, whether they also hold in the reverse direction (i.e., from linguistic to mathematical processing). In a questionnaire-based experiment, participants had to solve structurally left- or right-branching equations (e.g., 5 × 2 + 7 versus 5 + 2 × 7) and to provide sensicality ratings for structurally left- or right-branching adjective–noun–noun compounds (e.g., alien monster movie versus lengthy monster movie). In the first version of the experiment, the equations were used as primes and the linguistic expressions as targets (investigating structural priming from maths to language). In the second version, the order was reversed (language-to-maths priming). Both versions of the experiment showed clear structural priming effects, conceptually replicating and extending the findings from Scheepers and colleagues (2011). Most crucially, the observed bidirectionality of cross-domain structural priming strongly supports the notion of shared syntactic representations (or recursive procedures to generate and parse them) between arithmetic and language.

Inability to access addiction treatment among street-involved youth in a Canadian setting

From Sept 2005 to May 2012, 1015 street-involved youth were enrolled into the At-Risk Youth Study, a prospective cohort of youth aged 14-26 who use illicit drugs in Vancouver, Canada. Data were collected through semiannual interviewer administered questionnaires. Generalized estimating equation logistic regression was used to identify factors independently associated with being unable to access addiction treatment. The enclosed manuscript notes the implications and limitations of this study, as well as possible directions for future research. This study was funded by the US National Institutes of Health (NIH) and Canadian Institutes of Health (CIHR).

Crack pipe sharing among street-involved youth in a Canadian setting

INTRODUCTION AND AIMS

Crack pipe sharing is a risky practice that has been associated with the transmission of hepatitis C and other harms. While previous research has exclusively focused on this phenomenon among adults, this study examines crack pipe sharing among street-involved youth.

DESIGN AND METHODS

From May 2006 to May 2012, data were collected from the At-Risk Youth Study, a cohort of street-involved youth aged 14-26 in Vancouver, Canada. Survey data from active crack smokers were analysed using generalised estimating equations logistic regression.

RESULTS

Over the study period, 567 youth reported smoking crack cocaine and contributed 1288 observations, among which 961 (75%) included a report of crack pipe sharing. In multivariate analysis, factors that were associated with crack pipe sharing included difficulty accessing crack pipes [adjusted odds ratio (AOR) = 1.58, 95% confidence interval (CI) 1.13-2.20]; homelessness (AOR = 1.87, 95% CI 1.43-2.44); regular employment (AOR = 1.53, 95% CI 1.15-2.04); daily non-injection crystal methamphetamine use (AOR = 2.04, 95% CI 1.11-3.75); daily crack smoking (AOR = 1.37, 95% CI 1.01-1.85); encounters with the police (AOR = 1.42, 95% CI 1.01-1.99); and reporting unprotected sex (AOR = 1.95, 95% CI 1.47-2.58).

DISCUSSION AND CONCLUSIONS

The prevalence of crack pipe sharing was high among our sample and independently associated with structural factors including difficulty accessing crack pipes and homelessness. Crack pipe sharing was also associated with high-intensity drug use and a number of other markers of risk and vulnerability. Collectively, these findings highlight opportunities for health services to better engage with this vulnerable group and reduce this risky behaviour.

Measuring family HRQoL spillover effects using direct health utility assessment

Background. Applications of cost-effectiveness analysis do not typically incorporate effects on caregiver quality of life despite increasing evidence that these effects are measurable. Methods. Using a national sample of US adults, we conducted 2 cross-sectional surveys during December 2011 and January 2012. One version asked respondents to value their own experience as the family member of a person with a chronic illness (experienced sample), and the other version asked respondents to value hypothetical scenarios describing the experience of having a family member with a chronic illness (community sample). Conditions included Alzheimer’s disease/dementia, arthritis, cancer, and depression. Using standard gamble questions, respondents were asked to value the spillover effects of a family member’s illness. We used regression analysis to evaluate the disutility (loss in health-related quality of life) of having a family member with a chronic illness by condition and relationship type, controlling for the respondent’s own conditions and sociodemographic characteristics. Results. For the experienced sample (n = 1389), regression analyses suggested that greater spillover was associated with certain conditions (arthritis, depression) compared with other conditions (Alzheimer’s disease, cancer). For the community sample (n = 1205), regression analyses indicated that lower spillover was associated with condition (cancer) but not the type of relationship with the ill family member (parent, child, spouse). Conclusions. The effects of illness extend beyond the individual patient to include effects on caregivers of patients, parents of ill children, spouses, and other close family and household members. Cost-effectiveness analyses should consider the inclusion of health-related quality of life spillover effects in addition to caregiving time costs incurred by family members of ill individuals.

Does walking speed mediate the association between visual impairment and self-report of mobility disability? The Salisbury Eye Evaluation Study

OBJECTIVES

To determine whether performance speeds mediate the association between visual impairment and self-reported mobility disability over an 8-year period.

DESIGN

Longitudinal analysis.

SETTING

Salisbury, Maryland.

PARTICIPANTS

Salisbury Eye Evaluation Study participants aged 65 and older (N=2,520).

MEASUREMENTS

Visual impairment was defined as best-corrected visual acuity worse than 20/40 in the better-seeing eye or visual field less than 20°. Self-reported mobility disability on three tasks was assessed: walking up stairs, walking down stairs, and walking 150 feet. Performance speed on three similar tasks was measured: walking up steps (steps/s), walking down steps (steps/s), and walking 4 m (m/s).

RESULTS

For each year of observation, the odds of reporting mobility disability was significantly greater for participants who were visually impaired (VI) than for those who were not (NVI) (odds ratio (OR) difficulty walking up steps=1.58, 95% confidence interval (CI)=1.32-1.89; OR difficulty walking down steps=1.90, 95% CI=1.59-2.28; OR difficulty walking 150 feet=2.11, 95% CI=1.77-2.51). Once performance speed on a similar mobility task was included in the models, VI participants were no longer more likely to report mobility disability than those who were NVI (OR difficulty walking up steps=0.84, 95% CI=0.65-1.11; OR difficulty walking down steps=0.96, 95% CI=0.74-1.24; OR difficulty walking 150 feet=1.22, 95% CI=0.98-1.50).

CONCLUSION

Slower performance speed in VI individuals largely accounted for the difference in the odds of reporting mobility disability, suggesting that VI older adults walk slower and are therefore more likely to report mobility disability than those who are NVI. Improving mobility performance in older adults with visual impairment may minimize the perception of mobility disability.

High prevalence and partner correlates of physical and sexual violence by intimate partners among street and off-street sex workers

Objectives

Intimate partner violence (IPV) is associated with increased risk of HIV among women globally. There is limited evidence and understanding about IPV and potential HIV risk pathways among sex workers (SWs). This study aims to longitudinally evaluate prevalence and correlates of IPV among street and off-street SWs over two-years follow-up.

Methods

Longitudinal data were drawn from an open prospective cohort, AESHA (An Evaluation of Sex Workers Health Access) in Metro Vancouver, Canada (2010–2012). Prevalence of physical and sexual IPV was measured using the WHO standardized IPV scale (version 9.9). Bivariate and multivariable logistic regression using Generalized Estimating Equations (GEE) were used to examine interpersonal and structural correlates of IPV over two years.

Results

At baseline, 387 SWs had a male, intimate sexual partner and were eligible for this analysis. One-fifth (n = 83, 21.5%) experienced recent physical/sexual IPV at baseline and 26.2% over two-years follow-up. In multivariable GEE analysis, factors independently correlated with physical/sexual IPV in the last six months include: childhood (<18 years) sexual/physical abuse (adjusted odds ratio [AOR] = 2.05, 95% confidence interval [CI]: 1.14–3.69), inconsistent condom use for vaginal and/or anal sex with intimate partner (AOR = 1.84, 95% CI: 1.07–3.16), <daily prescription opioid use (AOR = 1.72, 95% CI: 1.02–2.89), providing financial support to intimate partner (AOR = 1.65, 95% CI: 1.05–2.59), and sourcing drugs from intimate partner (AOR = 1.62, 95% CI: 1.02–2.26).

Discussion

Our results demonstrate that over one-fifth of SWs in Vancouver report physical/sexual IPV in the last six months. The socio-structural correlates of IPV uncovered here highlight potential HIV risk pathways through SWs’ intimate, non-commercial partner relationships. The high prevalence of IPV among SWs is a critical public health concern and underscores the need for integrated violence and HIV prevention and intervention strategies tailored to this key population.

Spatio-temporal dynamics of parasites infecting Diporeia spp. (Amphipoda, Gammaridae) in southern Lake Michigan (USA)

Since the 1990s, populations of the benthic amphipod Diporeia spp. (Diporeia) have sharply declined across much of the Laurentian Great Lakes. This study was undertaken to identify contemporary and historical community composition, structure, and dynamics of parasites infecting Diporeia collected from nine sites in the southern basin of Lake Michigan, where declines of the amphipod have been well documented over the past 20years. An additional aim of this study was to assess whether infection dynamics and dreissenid densities could explain the declines in Diporeia densities that have occurred. We found that Diporeia were host to eight groups of uni- and multicellular pathogens. Of the 3082 amphipods analyzed, 1624 individuals (52.7%) were infected with at least one type of parasite. Ciliophora was the most prevalent parasite (50.08% prevalence of infection), followed by Gregarinasina (2.79%), Microsporidia (0.68%), Cestoda (0.45%), Acanthocephala (0.36%), Haplosporidia (0.23%), Yeast (0.32%), and filamentous Fungi (0.10%). Considerable spatial and temporal variability were observed in parasite prevalences, with prevalences frequently appearing to cycle between low and high values. Parasite species belonging to Microsporidia and Haplosporidia were associated with tissue alteration and host inflammatory response; however, parasite prevalences explained very little in terms of Diporeia density declines at assessed sites. Despite these findings, we do not discount the possibility that parasitic infections may have played a role in declining Diporeia densities in the Great Lakes, as the cyclical prevalences that were observed are possibly suggestive of parasitic outbreaks that are followed by die-offs at affected sites. This study suggests that if parasites have affected Diporeia densities in the Laurentian Great Lakes, then the relationship may be a complicated one.

Core symptoms not meeting criteria for delirium are associated with cognitive and functional impairment and mood and behavior problems in older long-term care residents

BACKGROUND

The immediate clinical significance of Confusion Assessment Method (CAM)-defined core symptoms of delirium not meeting criteria for delirium is unclear. This study proposed to determine if such symptoms are associated with cognitive and functional impairment, mood and behavior problems and increased Burden of Care (BOC) in older long-term care (LTC) residents.

METHODS

The study was a secondary analysis of data collected for a prospective cohort study of delirium. Two hundred and fifty-eight LTC residents aged 65 years and older in seven LTC facilities had monthly assessments (for up to six months) of CAM - defined core symptoms of delirium (fluctuation, inattention, disorganized thinking, and altered level of consciousness) and five outcome measures: Mini-Mental State Exam, Barthel Index, Cornell Scale for Depression, Nursing Home Behavioral Problems Scale, and Burden of Care. Associations between core symptoms and the five outcome measures were analyzed using generalized estimating equations.

RESULTS

Core symptoms of delirium not meeting criteria for delirium among residents with and without dementia were associated with cognitive and functional impairment and mood and behavior problems but not increased BOC. The associations appear to be intermediate between those of full delirium and no core symptoms and were greater for residents with than without dementia.

CONCLUSION

CAM-defined core symptoms of delirium not meeting criteria for delirium appear to be associated with cognitive and functional impairment and mood and behavior problems in LTC residents with or without dementia. These findings may have implications for the prevention and management of such impairments and problems in LTC settings.

Uniting statistical and individual-based approaches for animal movement modelling

The dynamic nature of their internal states and the environment directly shape animals' spatial behaviours and give rise to emergent properties at broader scales in natural systems. However, integrating these dynamic features into habitat selection studies remains challenging, due to practically impossible field work to access internal states and the inability of current statistical models to produce dynamic outputs. To address these issues, we developed a robust method, which combines statistical and individual-based modelling. Using a statistical technique for forward modelling of the IBM has the advantage of being faster for parameterization than a pure inverse modelling technique and allows for robust selection of parameters. Using GPS locations from caribou monitored in Québec, caribou movements were modelled based on generative mechanisms accounting for dynamic variables at a low level of emergence. These variables were accessed by replicating real individuals' movements in parallel sub-models, and movement parameters were then empirically parameterized using Step Selection Functions. The final IBM model was validated using both k-fold cross-validation and emergent patterns validation and was tested for two different scenarios, with varying hardwood encroachment. Our results highlighted a functional response in habitat selection, which suggests that our method was able to capture the complexity of the natural system, and adequately provided projections on future possible states of the system in response to different management plans. This is especially relevant for testing the long-term impact of scenarios corresponding to environmental configurations that have yet to be observed in real systems.

Systemic glucose variability predicts cerebral metabolic distress and mortality after subarachnoid hemorrhage: a retrospective observational study

Introduction

Cerebral glucose metabolism and energy production are affected by serum glucose levels. Systemic glucose variability has been shown to be associated with poor outcome in critically ill patients. The objective of this study was to assess whether glucose variability is associated with cerebral metabolic distress and outcome after subarachnoid hemorrhage.

Methods

A total of 28 consecutive comatose patients with subarachnoid hemorrhage, who underwent cerebral microdialysis and intracranial pressure monitoring, were studied. Metabolic distress was defined as lactate/pyruvate ratio (LPR) >40. The relationship between daily glucose variability, the development of cerebral metabolic distress and hospital outcome was analyzed using a multivariable general linear model with a logistic link function for dichotomized outcomes.

Results

Daily serum glucose variability was expressed as the standard deviation (SD) of all serum glucose measurements. General linear models were used to relate this predictor variable to cerebral metabolic distress and mortality at hospital discharge. A total of 3,139 neuromonitoring hours and 181 days were analyzed. After adjustment for Glasgow Coma Scale (GCS) scores and brain glucose, SD was independently associated with higher risk of cerebral metabolic distress (adjusted odds ratio = 1.5 (1.1 to 2.1), P = 0.02). Increased variability was also independently associated with in hospital mortality after adjusting for age, Hunt Hess, daily GCS and symptomatic vasospasm (P = 0.03).

Conclusions

Increased systemic glucose variability is associated with cerebral metabolic distress and increased hospital mortality. Therapeutic approaches that reduce glucose variability may impact on brain metabolism and outcome after subarachnoid hemorrhage.

Excessive daytime sleepiness among rural residents in Saskatchewan

BACKGROUND

Obstructive sleep apnea (OSA) is a common diagnosis in clinical practice. Excessive daytime sleepiness may be a warning for possible OSA.

OBJECTIVES

To assess the prevalence of excessive daytime sleepiness as measured by the Epworth Sleepiness Scale (ESS) in a rural community population; potential risk factors for OSA were also assessed.

METHODS

In 2010, a baseline respiratory health questionnaire within the Saskatchewan Rural Health Study was mailed to 11,982 households in Saskatchewan. A total of 7597 adults within the 4624 (42%) respondent households completed the ESS questionnaire. Participants were categorized according to normal or high (>10) ESS scores. Data obtained included respiratory symptoms, doctor-diagnosed sleep apnea, snoring, hypertension, smoking and demographics. Body mass index was calculated. Multivariable logistic regression analysis examined associations between high ESS scores and possible risk factors. Generalized estimating equations accounted for the two-tiered sampling procedure of the study design.

RESULTS

The mean age of respondents was 55.0 years and 49.2% were male. The prevalence of ESS>10 and 'doctor diagnosed' OSA were 15.9% and 6.0%, respectively. Approximately 23% of respondents reported loud snoring and 30% had a body mass index >30 kg⁄m2. Of those with 'doctor-diagnosed' OSA, 37.7% reported ESS>10 (P<0.0001) and 47.7% reported loud snoring (P<0.0001). Risk of having an ESS>10 score increased with age, male sex, obesity, lower socioeconomic status, marriage, loud snoring and doctor-diagnosed sinus trouble.

CONCLUSIONS

High levels of excessive daytime sleepiness in this particular rural population are common and men >55 years of age are at highest risk. Examination of reasons for residual sleepiness and snoring in persons with and without sleep apnea is warranted.

Distribution of Culicoides sonorensis (Diptera: Ceratopogonidae) in Alberta, Canada

The distribution of Culicoides sonorensis Wirth and Jones was examined in Alberta, Canada. Sampling was conducted weekly using blacklight traps at eight locations in 2009, and 10 locations during 2010-2012. Nine supplemental sites were sampled twice annually during both 2011 and 2012. Abundance of C. sonorensis was consistently greatest at a site near the U.S. border, and declined in a northerly direction. Mean annual abundance at this site ranged from 6.4- to > 1,000-fold greater across positive sites. Data from a less extensive survey conducted during 2002-2006 were included in the remaining analyses. C. sonorensis was distributed below a diagonal spanning 49 degrees 30' N, 113 degrees 0' W to 51 degrees 21' N, 110 degrees 40' W. The relationship between the proportion of weekly samples positive and mean annual abundance at a site was determined and indicated that the proportion of positive samples could be used as a surrogate measure of abundance to overcome issues associated with the extreme variation in abundance. A series of logistic regression models were developed and evaluated to determine the effects of spatial (latitude and longitude), climatic (historic temperature and precipitation during the warmest quarter), and weather (temperature during the sample interval and spring precipitation) on abundance as measured by the proportion of positive samples. Spatial and climatic variables set the overall level of abundance, while weather variables added seasonal fluctuations within years, and also fluctuations between years. These data will be useful for long-term monitoring of C. sonorensis and as a baseline for detecting shifts in abundance that might occur because of climate change.

Increases and decreases in drug use attributed to housing status among street-involved youth in a Canadian setting

Background

Among a cohort of drug-using street-involved youth, we sought to identify the prevalence of reporting increases and decreases in illicit drug use due to their current housing status and to identify factors associated with reporting these changes.

Findings

This longitudinal study was based on data collected between June 2008 and May 2012 from a prospective cohort of street-involved youth aged 14–26 in Vancouver, Canada. At semi-annual study follow-up visits, youth were asked if their drug use was affected by their housing status. Using generalized estimating equations, we identified factors associated with perceived increases and decreases in drug use attributed to housing status. Among our sample of 536 participants at baseline, 164 (31%) youth reported increasing their drug use due to their housing situation and 71 (13%) reported decreasing their drug use. In multivariate analysis, factors that were positively associated with perceived increases in drug use attributed to housing status included the following: being homeless, engaging in sex work and drug dealing. Regular employment was negatively associated with increasing drug use due to housing status. Among those who reported decreasing their drug use, only homelessness was significant in bivariate analysis.

Conclusion

Perceived changes in drug use due to housing status were relatively common in this setting and were associated with being homeless and, among those who increased their drug use, engaging in risky income generation activities. These findings suggest that structural factors, particularly housing and economic opportunities, may be crucial interventions for reducing or limiting drug use among street-involved youth.

Evaluation of serum thyroid-stimulating hormone as indicator for fine-needle aspiration in patients with thyroid nodules

BACKGROUND

Recently, it has been reported that the risk of thyroid malignancy increases with increasing concentrations of serum thyroid-stimulating hormone (TSH). The purpose of this study was to determine whether or not serum TSH can be a predictor for thyroid malignancy when considering the relevant ultrasound features and clinical risk factors.

METHODS

This retrospective study included 1200 euthyroid patients with 1269 thyroid nodules who underwent ultrasound-guided fine-needle aspiration (FNA) biopsy between January and June 2009. Serum TSH, ultrasound feature, and clinical parameters were compared according to final diagnosis. Subgroup analyses were performed according to nodule size.

RESULTS

Serum TSH did not show a positive association with malignancy for all nodules and the micronodule subgroup in multivariate analysis, although they showed significant association with thyroid malignancy for the macronodule subgroup. For all nodules and the 2 subgroups, suspicious ultrasound features and younger age were significantly associated with malignancy in univariate and multivariate analyses.

CONCLUSION

Our study suggests that TSH alone is not as useful as ultrasound features in deciding whether or not to perform FNA in patients with micronodules.

Parasite-mediated selection drives an immunogenetic trade-off in plains zebras (Equus quagga)

Pathogen evasion of the host immune system is a key force driving extreme polymorphism in genes of the major histocompatibility complex (MHC). Although this gene family is well characterized in structure and function, there is still much debate surrounding the mechanisms by which MHC diversity is selectively maintained. Many studies have investigated relationships between MHC variation and specific pathogens, and have found mixed support for and against the hypotheses of heterozygote advantage, frequency-dependent or fluctuating selection. Few, however, have focused on the selective effects of multiple parasite types on host immunogenetic patterns. Here, we examined relationships between variation in the equine MHC gene, ELA-DRA, and both gastrointestinal (GI) and ectoparasitism in plains zebras (Equus quagga). Specific alleles present at opposing population frequencies had antagonistic effects, with rare alleles associated with increased GI parasitism and common alleles with increased tick burdens. These results support a frequency-dependent mechanism, but are also consistent with fluctuating selection. Maladaptive GI parasite 'susceptibility alleles' were reduced in frequency, suggesting that these parasites may play a greater selective role at this locus. Heterozygote advantage, in terms of allele mutational divergence, also predicted decreased GI parasite burden in genotypes with a common allele. We conclude that an immunogenetic trade-off affects resistance/susceptibility to parasites in this system. Because GI and ectoparasites do not directly interact within hosts, our results uniquely show that antagonistic parasite interactions can be indirectly modulated through the host immune system. This study highlights the importance of investigating the role of multiple parasites in shaping patterns of host immunogenetic variation.

Alcohol craving in adolescents: bridging the laboratory and natural environment

RATIONALE

Initial lab studies suggest that adolescent drinkers crave alcohol when presented with alcohol cues. Whether this effect generalizes to the natural environment, however, remains unknown, and studies have not examined whether craving predicts drinking among youths.

OBJECTIVES

This study builds on existing research by pairing controlled lab-based cue reactivity assessments (CRAs) with data collected in the natural environment using ecological momentary assessment (EMA) methods. We examined whether alcohol cues evoke craving among adolescent drinkers in the lab and natural environment, and tested the clinical relevance of craving during adolescence by examining the prospective association between craving and alcohol use.

METHODS

Non-treatment-seeking adolescent drinkers (N = 42; ages 15 to 20 years) completed a lab-based CRA followed by a 1-week EMA monitoring period. During the EMA period, youth were prompted randomly throughout the day to record momentary data on craving and contextual factors (e.g., alcohol cues, peers present).

RESULTS

Alcohol cues elicited craving in the lab, and this effect generalized to the natural environment, especially among adolescents with more alcohol problems. In addition, craving predicted subsequent drinking levels in the natural environment.

CONCLUSIONS

This study demonstrates the utility of pairing lab paradigms with EMA methods to better characterize adolescents' reactivity to alcohol cues. Results implicate craving as a clinically meaningful motivator for drinking among adolescents and highlight a potentially important target of pharmacological or behavioral intervention.

Exploring the variation in state-level prescription utilization using a triangulation of analytic methods

BACKGROUND

Retail prescription fill data have consistently shown wide variation in prescription drug utilization across states, with state-level rates ranging from 8.5 to 19.3 filled prescriptions per capita per year. Empirical explanations for this wide variation have not yet been sought.

OBJECTIVES

To examine which factors potentially explain the wide variation in prescription drug utilization across US states.

METHODS

Summary data (proportions, counts, rates, etc) on sociodemographics, health, insurance, provider density, health service use, and retail prescription drug fills for each of the 50 states and the District of Columbia, from 2008 to 2010, were retrieved from multiple national data sources, such as the Kaiser Family Foundation's "State Health Facts" Web Portal. Pooled cross-sectional linear, negative binomial, and ordered logit multivariable regressions were used to model states' prescription utilization as a function of the aforementioned possible explanatory variables. Principal components analysis also was employed so as to overcome high correlations among some of the covariates.

RESULTS

Among US states, higher levels of employer-sponsored insurance or Medicaid coverage were associated with both higher levels of prescription utilization and a higher likelihood of being in upper utilization quartiles. A higher density of nurse practitioners was also positively associated with both the level of utilization and the likelihood of higher utilization, whereas a higher density of active physicians was associated with opposite effects. Higher prevalence of physical activity was associated with lower utilization levels as well as a lower likelihood of high utilization. State-level prevalence of chronic conditions and poor health mattered only for the level of prescription utilization. States' sociodemographics were not significantly associated with prescription utilization.

CONCLUSIONS

This study suggests that higher prescription utilization across states was associated with the variations in provider types, Medicaid and private insurance coverage, as well as the prevalence of chronic diseases. Further investigation of how each of these factors may contribute to a particular state's prescription drug utilization level is needed.

Cumulative mechanical low-back load at work is a determinant of low-back pain

OBJECTIVES

Reported associations of physical exposures during work (eg, lifting, trunk flexion or rotation) and low-back pain (LBP) are rather inconsistent. Mechanical back loads (eg, moments on the low back) as a result of exposure to abovementioned risk factors have been suggested to be important as such loads provide a more direct relationship with tissue failure and thus LBP. Since information on the effect of such load metrics with LBP is lacking yet, we aimed to assess this effect in a prospective study.

METHODS

Of 1131 workers, categorised into 19 groups, LBP was prospectively assessed over 3 years. Video and hand force recordings of 4-5 workers per group (93 in total) were used to estimate mechanical low-back loads (peak load and three cumulative load metrics, ie, linear weighted load, squared weighted load and load weighted to the tenth power) during manual materials handling (MMH) tasks using a video analysis method. These data were combined with static mechanical load estimates based on structured observation of non-MMH tasks. Associations of mechanical loads and LBP were tested using generalised estimating equations.

RESULTS

Significant effects on LBP were found for cumulative low-back moments (linear and squared weighted; both p<0.01 and ORs of 3.01 and 3.50, respectively) but not for peak and cumulative moments weighted to the tenth power.

CONCLUSIONS

Results of this first prospective study on the effect of mechanical low-back load on LBP support a LBP aetiology model of cumulative loads, potentially due to accumulation of microdamage or fatigue. Therefore, prevention of LBP should focus on reducing cumulative low-back loads, especially in highly exposed occupational groups, for example, by reducing handling of heavy loads and working in awkward body postures.

Trends in live birth rates and adverse neonatal outcomes among HIV-positive women in Ontario, Canada, 2002-2009: a descriptive population-based study

To characterise trends in live birth rates, adverse neonatal outcomes and socio-demographic characteristics of pregnant women with diagnosed HIV between the ages of 18 and 49 in Ontario, Canada from 1 April 2002 to 31 March 2010, we conducted a population-based study. Utilising linked administrative healthcare databases we used generalised estimating equations to characterise secular trends and examine the association between live births and socio-demographic characteristics, including age, region of birth and neighbourhood income quintile. Between 2002/2003 and 2009/2010, there were 551 live births during 15,610 person-years of follow-up. The proportion of HIV-positive mothers originally from Africa or the Caribbean increased from 26.7% to 51.6% over the study period. The risk of pre-term (risk ratio 2.13, 95% confidence interval 1.74 to 2.61) and small for gestational age births (risk ratio 1.53, 95% confidence interval 1.20 to 1.94) was higher in women with HIV compared with provincial estimates for these outcomes. Women with HIV have rates of pre-term and small for gestational age births that exceed provincial estimates for these outcomes. Further research is required to identify factors mediating these disparities that are amenable to pre-natal risk reduction initiatives.

Frequent and seasonally variable sublethal anthrax infections are accompanied by short-lived immunity in an endemic system

Few studies have examined host-pathogen interactions in wildlife from an immunological perspective, particularly in the context of seasonal and longitudinal dynamics. In addition, though most ecological immunology studies employ serological antibody assays, endpoint titre determination is usually based on subjective criteria and needs to be made more objective. Despite the fact that anthrax is an ancient and emerging zoonotic infectious disease found world-wide, its natural ecology is not well understood. In particular, little is known about the adaptive immune responses of wild herbivore hosts against Bacillus anthracis. Working in the natural anthrax system of Etosha National Park, Namibia, we collected 154 serum samples from plains zebra (Equus quagga), 21 from springbok (Antidorcas marsupialis) and 45 from African elephants (Loxodonta africana) over 2-3 years, resampling individuals when possible for seasonal and longitudinal comparisons. We used enzyme-linked immunosorbent assays to measure anti-anthrax antibody titres and developed three increasingly conservative models to determine endpoint titres with more rigourous, objective mensuration. Between 52 and 87% of zebra, 0-15% of springbok and 3-52% of elephants had measurable anti-anthrax antibody titres, depending on the model used. While the ability of elephants and springbok to mount anti-anthrax adaptive immune responses is still equivocal, our results indicate that zebra in ENP often survive sublethal anthrax infections, encounter most B. anthracis in the wet season and can partially booster their immunity to B. anthracis. Thus, rather than being solely a lethal disease, anthrax often occurs as a sublethal infection in some susceptible hosts. Though we found that adaptive immunity to anthrax wanes rapidly, subsequent and frequent sublethal B. anthracis infections cause maturation of anti-anthrax immunity. By triggering host immune responses, these common sublethal infections may act as immunomodulators and affect population dynamics through indirect immunological and co-infection effects. In addition, with our three endpoint titre models, we introduce more mensuration rigour into serological antibody assays, even under the often-restrictive conditions that come with adapting laboratory immunology methods to wild systems. With these methods, we identified significantly more zebras responding immunologically to anthrax than have previous studies using less comprehensive titre analyses.

Importance of social and cultural factors for attitudes, disclosure and time off work for depression: findings from a seven country European study on depression in the workplace

OBJECTIVES

Depression is experienced by a large proportion of the workforce and associated with high costs to employers and employees. There is little research on how the social costs of depression vary by social and cultural context. This study investigates individual, workplace and societal factors associated with greater perceived discomfort regarding depression in the workplace, greater likelihood of employees taking time off of work as a result of depression and greater likelihood of disclosure of depression to one's employer.

METHODS

Employees and managers (n = 7,065) were recruited from seven European countries to participate in the IDEA survey. Multivariable logistic regression models were used to examine associations between individual characteristics and country contextual characteristics in relation to workplace perceptions, likelihood of taking time off work and disclosing depression to an employer.

RESULTS

Our findings suggest that structural factors such as benefit systems and flexible working hours are important for understanding workplace perceptions and consequences for employees with depression. However, manager responses that focus on offering help to the employee with depression appear to have stronger associations with positive perceptions in the workplace, and also with openness and disclosure by employees with depression.

CONCLUSION

This study highlights the importance of individual, workplace and societal factors that may be associated with how people with depression are perceived and treated in the workplace, and, hence, factors that may be associated with openness and disclosure among employees with depression. Some responses, such as flexible working hours, may be helpful but are not necessarily sufficient, and our findings also emphasise the importance of support and openness of managers in addition to flexible working hours.

Model selection criterion for causal parameters in structural mean models based on a quasi-likelihood

Structural mean models (SMMs) have been proposed for estimating causal parameters in the presence of non-ignorable non-compliance in clinical trials. To obtain a valid causal estimate, we must impose several assumptions. One of these is the correct specification of the structural model. Building on Pan's work (2001, Biometrics 57, 120-125) on developing a model selection criterion for generalized estimating equations, we propose a new approach for model selection of SMMs based on a quasi-likelihood. We provide a formal model selection criterion that is an extension of Akaike's information criterion. Using subset selection of baseline covariates, our method allows us to understand whether the treatment effect varies across the available baseline covariate levels, and/or to quantify the treatment effect on a specific covariates level to target specific individuals to maximize treatment benefit. We present simulation results in which our method performs reasonably well compared to other testing methods in terms of both the probability of selecting the correct model and the predictive performances of the individual treatment effects. We use a large randomized clinical trial of pravastatin as a motivation.

Does electroencephalogram phase variability account for reduced P3 brain potential in externalizing disorders?

OBJECTIVE

Amplitude deficits of the P3 event-related potential (ERP) are associated with externalizing psychopathology but little is known about the nature of underlying brain electrical activity that accounts for this amplitude reduction. We sought to understand if group differences in task-induced phase-locking in electroencephalographic (EEG) delta and theta frequencies may account for P3-externalizing associations.

METHODS

Adult males (N=410) completed a visual oddball task and frontal and parietal P3-related delta- and theta-band phase-invariant evoked energy and inter-trial phase-locking measures were investigated with respect to the externalizing spectrum, including substance dependence, adult antisociality, and childhood disruptive disorders. We hypothesized that P3-related phase-locking is weaker in externalizing-diagnosed individuals and this might mediate prior findings of reduced evoked P3 energy.

RESULTS

Reductions in both evoked energy and phase-locking, in both frequency bands, at both scalp sites, were associated with greater odds of externalizing diagnoses. Generally, adding phase-locking to evoked energy came with better prediction model fit. Moreover, reduced theta-band phase-locking partially mediated the effects of within-frequency evoked energy on externalizing prediction.

CONCLUSIONS

Inter-trial phase-locking underlying P3 appears to be an important distinction between externalizing and control subjects.

SIGNIFICANCE

This cross-trial phase-variability for externalizing-diagnosed individuals might reflect deficient top-down "tuning" by neuromodulatory systems.

Associations between injection risk and community disadvantage among suburban injection drug users in southwestern Connecticut, USA

Increases in drug abuse, injection, and opioid overdoses in suburban communities led us to study injectors residing in suburban communities in southwestern Connecticut, US. We sought to understand the influence of residence on risk and injection-associated diseases. Injectors were recruited by respondent-driven sampling and interviewed about sociodemographics, somatic and mental health, injection risk, and interactions with healthcare, harm reduction, substance abuse treatment, and criminal justice systems. HIV, hepatitis B and C (HBV and HCV) serological testing was also conducted. Our sample was consistent in geographic distribution and age to the general population and to the patterns of heroin-associated overdose deaths in the suburban towns. High rates of interaction with drug abuse treatment and criminal justice systems contrasted with scant use of harm reduction services. The only factors associated with both dependent variables-residence in less disadvantaged census tracts and more injection risk-were younger age and injecting in one's own residence. This contrasts with the common association among urban injectors of injection-associated risk behaviors and residence in disadvantaged communities. Poor social support and moderate/severe depression were associated with risky injection practices (but not residence in specific classes of census tracts), suggesting that a region-wide dual diagnosis approach to the expansion of harm reduction services could be effective at reducing the negative consequences of injection drug use.

Identifying factors associated with changes in physical functioning in an older population

AIM

The present study evaluated the association between changes in physical functioning and a variety of factors in an older population in Taiwan.

METHODS

The data of 907 participants were derived from a three-wave cohort study of aging, the Functioning and Aging Study in Taipei, with a study period from 2005 to 2009. Functional status was assessed using activities of daily living, instrumental activities of daily living and mobility tasks, and classified as being normal, with mild disability, moderate disability, and severe disability. All potential factors were allocated into five groups including demography, chronic diseases, geriatric conditions, lifestyle and physical assessments. Generalized estimating equations and generalized linear mixed-effects models were used to identify factors responsible for changes in physical functioning across different waves of data.

RESULTS

The proportion of elderly participants with normal function decreased with time throughout the study period. The results of Generalized estimating equations and mixed effects models showed nearly identical sets of factors. These included age, living arrangements, social support, self-rated health, stroke, diabetes, Parkinson's disease, osteoporosis, depression, cognition, vision, history of fracture and falls, incontinence of urine and feces, physical activity, body mass index, and short physical performance battery.

CONCLUSIONS

Older persons with stroke, Parkinson's disease, diabetes, osteoporosis, geriatric conditions and poor short physical performance battery score should be considered as the target of prevention against functional decline. Those not living with spouses, with poor self-rated health, with low social support, being underweight or obese and with a sedentary lifestyle might also require major attention.

Prevalence of hypertension and associated factors in an indigenous community of central Brazil: a population-based study

Objective

The aim of the present study was to assess the prevalence of hypertension and cardiovascular risk factors among the native indigenous of Jaguapiru village in Dourados, Mato Grosso do Sul, Brazil.

Method

A cross-sectional, population-based study was conducted with adult indigenous aged 18 years or more. The subjects' blood pressure was measured twice, and the mean of the two measurements was calculated. Body weight, height, capillary blood glucose and waist circumference were measured. Pregnant women, individuals using glucocorticoids, and non-indigenous villagers and their offspring were excluded. Multivariate regression analyses were conducted on the socio-demographic and clinical independent variables. Interactions between independent variables were also tested.

Results

We included 1,608 native indigenous eligible to the research. The prevalence of hypertension was 29.5% (95% CI: 27–31.5), with no significant difference between the genders. For both men and women, diastolic hypertension was more common than systolic hypertension. The prevalence of hypertension was higher among obese, diabetic, and older participants, as well as those who consumed alcohol, had a lower educational level, or had a family history of hypertension. There was no association between hypertension and tobacco smoking or family income.

Conclusion

Hypertension among the indigenous from Jaguapiru village was similar to the prevalence in the Brazilians, but may have a more negative effect in such disadvantaged population. The associated factors we found can help drawing prevention policies.

Patient-specific computer-based decision support in primary healthcare--a randomized trial

BACKGROUND

Computer-based decision support systems are a promising method for incorporating research evidence into clinical practice. However, evidence is still scant on how such information technology solutions work in primary healthcare when support is provided across many health problems. In Finland, we designed a trial where a set of evidence-based, patient-specific reminders was introduced into the local Electronic Patient Record (EPR) system. The aim was to measure the effects of such reminders on patient care. The hypothesis was that the total number of triggered reminders would decrease in the intervention group compared with the control group, indicating an improvement in patient care.

METHODS

From July 2009 to October 2010 all the patients of one health center were randomized to an intervention or a control group. The intervention consisted of patient-specific reminders concerning 59 different health conditions triggered when the healthcare professional (HCP) opened and used the EPR. In the intervention group, the triggered reminders were shown to the HCP; in the control group, the triggered reminders were not shown. The primary outcome measure was the change in the number of reminders triggered over 12 months. We developed a unique data gathering method, the Repeated Study Virtual Health Check (RSVHC), and used Generalized Estimation Equations (GEE) for analysing the incidence rate ratio, which is a measure of the relative difference in percentage change in the numbers of reminders triggered in the intervention group and the control group.

RESULTS

In total, 13,588 participants were randomized and included. Contrary to our expectation, the total number of reminders triggered increased in both the intervention and the control groups. The primary outcome measure did not show a significant difference between the groups. However, with the inclusion of patients followed up over only six months, the total number of reminders increased significantly less in the intervention group than in the control group when the confounding factors (age, gender, number of diagnoses and medications) were controlled for.

CONCLUSIONS

Computerized, tailored reminders in primary care did not decrease during the 12 months of follow-up time after the introduction of a patient-specific decision support system.

TRIAL REGISTRATION

ClinicalTrial.gov NCT00915304.

Risk factor analysis for capsular contracture: a 5-year Sientra study analysis using round, smooth, and textured implants for breast augmentation

BACKGROUND

Although there are a few broadly agreed on contributory factors, the multifaceted causes of capsular contracture have remained unresolved for decades. This study investigates a variety of potential risk factors that contribute to capsular contracture in primary augmentation patients.

METHODS

The data used for this analysis include 5109 implants in 2560 primary augmentation patients implanted by 34 surgeons based on 5-year results from Sientra's clinical study. Patients were evaluated at annual visits where the capsular contracture Baker grade was recorded. Potential risk factors, including patient attributes, implant attributes, surgery characteristics, pocket irrigation, and postsurgery characteristics, were analyzed using frequency and multivariate models.

RESULTS

A total of 265 capsular contracture events in 179 patients were reported through 5 years. The overall Kaplan-Meier rate for capsular contracture was 7.6 percent by device. The unadjusted analysis showed increased odds of capsular contracture in smooth devices, periareolar incision, subglandular placement, antibiotic and steroid pocket irrigation, recommended massage, and surgical bra (p<0.05 for all). Results from the multivariate analysis, adjusting for all variables in the model, found six factors to be independently associated with capsular contracture (i.e., implant placement, implant surface, incision site, hematoma or seroma development, device size, and surgical bra; p<0.05 for all).

CONCLUSION

This analysis has provided evidence that submuscular placement and textured implants, in addition to other factors, are significant in reducing the incidence of capsular contracture.

Integrated assessment of behavioral and environmental risk factors for Lyme disease infection on Block Island, Rhode Island

Peridomestic exposure to Borrelia burgdorferi-infected Ixodes scapularis nymphs is considered the dominant means of infection with black-legged tick-borne pathogens in the eastern United States. Population level studies have detected a positive association between the density of infected nymphs and Lyme disease incidence. At a finer spatial scale within endemic communities, studies have focused on individual level risk behaviors, without accounting for differences in peridomestic nymphal density. This study simultaneously assessed the influence of peridomestic tick exposure risk and human behavior risk factors for Lyme disease infection on Block Island, Rhode Island. Tick exposure risk on Block Island properties was estimated using remotely sensed landscape metrics that strongly correlated with tick density at the individual property level. Behavioral risk factors and Lyme disease serology were assessed using a longitudinal serosurvey study. Significant factors associated with Lyme disease positive serology included one or more self-reported previous Lyme disease episodes, wearing protective clothing during outdoor activities, the average number of hours spent daily in tick habitat, the subject’s age and the density of shrub edges on the subject’s property. The best fit multivariate model included previous Lyme diagnoses and age. The strength of this association with previous Lyme disease suggests that the same sector of the population tends to be repeatedly infected. The second best multivariate model included a combination of environmental and behavioral factors, namely hours spent in vegetation, subject’s age, shrub edge density (increase risk) and wearing protective clothing (decrease risk). Our findings highlight the importance of concurrent evaluation of both environmental and behavioral factors to design interventions to reduce the risk of tick-borne infections.

Binge Drug Use among Street-Involved Youth in a Canadian Setting

BACKGROUND

Binge drug use has been associated with increased risk of HIV infection and other serious health-related harms among adult drug user populations. This study sought to determine the prevalence and correlates of binge drug use among street-involved youth in a Canadian setting.

METHODS

From Sept 2005 to May 2012, data were collected from the At-Risk Youth Study (ARYS), a prospective cohort of street-involved youth aged 14 - 26 who use illicit drugs. Multivariate generalized estimating equations (GEE) was used to identify factors associated with binge drug use.

RESULTS

Of the 987 participants included in this analysis, 41.5% reported binge drug use at baseline, and another 59.1% reported binge drug use at some point during the study. In multivariate GEE analysis, older age (adjusted odds ratio [AOR] = 1.11), homelessness (AOR = 1.67), drug injecting (AOR = 1.63), non-fatal overdose (AOR = 1.98), public injecting (AOR 1.42), being a victim of violence (AOR = 1.38), sex work (AOR = 2.51) and participation in drug dealing (AOR = 2.04) were independently associated with binge drug use in the previous 6 months (all p<0.05).

DISCUSSION

The prevalence of reporting binge drug use among the youth was high in this setting and was independently associated with a range of high-risk activities and markers of vulnerability. Querying high-risk youth about binge drug use may help prioritize those in greatest need of addiction treatment strategies and public health interventions.

Locally efficient estimation of marginal treatment effects when outcomes are correlated: is the prize worth the chase?

Semiparametric methods have been developed to increase efficiency of inferences in randomized trials by incorporating baseline covariates. Locally efficient estimators of marginal treatment effects, which achieve minimum variance under an assumed model, are available for settings in which outcomes are independent. The value of the pursuit of locally efficient estimators in other settings, such as when outcomes are multivariate, is often debated. We derive and evaluate semiparametric locally efficient estimators of marginal mean treatment effects when outcomes are correlated; such outcomes occur in randomized studies with clustered or repeated-measures responses. The resulting estimating equations modify existing generalized estimating equations (GEE) by identifying the efficient score under a mean model for marginal effects when data contain baseline covariates. Locally efficient estimators are implemented for longitudinal data with continuous outcomes and clustered data with binary outcomes. Methods are illustrated through application to AIDS Clinical Trial Group Study 398, a longitudinal randomized clinical trial that compared the effects of various protease inhibitors in HIV-positive subjects who had experienced antiretroviral therapy failure. In addition, extensive simulation studies characterize settings in which locally efficient estimators result in efficiency gains over suboptimal estimators and assess their feasibility in practice.

Obsessions and Time of Day: A Self-Monitoring Study in Individuals With Obsessive-Compulsive Disorder

Deepening our understanding of the basic mechanisms underlying obsessive-compulsive disorder (OCD) often leads to advances in clinical practice. And, as noted by Kazdin (2008), clinical experiences are an important resource for identifying novel targets for empirical study. One potential target for furthering our understanding of OCD is to investigate clinical reports of within-day symptom fluctuations. Self-monitoring data from 17 adults with OCD were used to test for a diurnal pattern in obsessions. Results from generalized estimating equations revealed that obsessions were most common during midday and that the midday exacerbation was briefer in males. In combination with prior findings of similar diurnal patterns for other anxious symptoms (e.g., panic), these findings suggest that daily social rhythms and/or circadian influences may influence levels of obsessions. Furthermore, treatment may be improved by attending to these heightened symptom periods and integrating this information into therapy (e.g., when developing the exposure hierarchy).