Akaike's information criterion in generalized estimating equations

Anemia is associated with metabolic distress and brain tissue hypoxia after subarachnoid hemorrhage

BACKGROUND

Anemia is frequently encountered in critically ill patients and adversely affects cerebral oxygen delivery and brain tissue oxygen (PbtO2). The objective of this study is to assess whether there is an association between anemia and metabolic distress or brain tissue hypoxia in patients with subarachnoid hemorrhage.

METHODS

Retrospective study was conducted in a neurological intensive care unit in a university hospital. Patients with subarachnoid hemorrhage that underwent multimodality monitoring with intracranial pressure, PbtO2 and microdialysis were analyzed. The relationships between hemoglobin (Hb) concentrations and brain tissue hypoxia (PbtO2 < or = 15 mmHg) and metabolic distress (lactate/pyruvate ratio > or =40) were analyzed with general linear models of logistic function for dichotomized outcomes utilizing generalized estimating equations.

RESULTS

A total of 359 matched neuromonitoring hours and Hb measurements were analyzed from 34 consecutive patients. The median hemoglobin was 9.7 g/dl (interquartile range 8.8-10.5). After adjusting for significant covariates, reduced hemoglobin concentration was associated with a progressively increased risk of brain tissue hypoxia (adjusted OR 1.7 [1.1-2.4]; P = 0.01 for every unit decrease). Also after adjusting for significant covariates, hemoglobin concentrations below 9 g/dl and between 9.1 and 10 g/dl were associated with an increased risk of metabolic distress as compared to concentrations between 10.1 and 11 g/dl (adjusted OR 3.7 [1.5-9.4]; P = 0.004 for Hb < or = 9 g/dl and adjusted OR 1.9 [1.1-3.3]; P = 0.03 for Hb 9.1-10 g/dl).

CONCLUSIONS

Anemia is associated with a progressively increased risk of cerebral metabolic distress and brain tissue hypoxia after subarachnoid hemorrhage.

Arsenic in drinking water and stroke hospitalizations in Michigan

BACKGROUND AND PURPOSE

Mechanistic and human studies suggest a role for arsenic in ischemic stroke; however, risks from chronic, low-level exposures are uncertain and US studies are lacking. The objective was to investigate the association between low-level arsenic exposure in drinking water and ischemic stroke hospital admissions in Michigan.

METHODS

Ischemic stroke hospital admissions among those aged ≥ 45 years were identified (1994 to 2006). Population-weighted average arsenic concentrations were estimated for each Michigan county (n = 83) and for zip codes in Genesee County (n=27) where there is greater variation in arsenic concentrations. US Census data provided age- and sex-specific population counts and other county- and zip code-level variables (race, income), which were adjusted for in multilevel negative binomial regression models of arsenic and stroke admissions. Hospital admissions for duodenal ulcer and hernia, not hypothesized to be associated with arsenic, were also evaluated.

RESULTS

Adjusted county-level analyses suggested a relationship between arsenic and ischemic stroke hospital admissions, although similar associations were observed for duodenal ulcer and hernia. In zip code-level analysis, arsenic was associated with an increased risk of stroke admission (relative risk, 1.03; 95% CI, 1.01 to 1.05 per μg/L increase in arsenic) after adjustment for confounders, and null or negative associations were found between arsenic and nonvascular outcomes.

CONCLUSIONS

Findings from this study suggest that exposure to even low levels of arsenic in drinking water may be associated with a higher risk of incident stroke. Given the ecological nature of the analysis, further epidemiological study with individual-level data on arsenic exposure and incident stroke is warranted.

Prediction models for incident type 2 diabetes mellitus in the older population: KORA S4/F4 cohort study

BACKGROUND

The aim was to derive Type 2 diabetes prediction models for the older population and to check to what degree addition of 2-h glucose measurements (oral glucose tolerance test) and biomarkers improves the predictive power of risk scores which are based on non-biochemical as well as conventional clinical parameters.

METHODS

Oral glucose tolerance tests were carried out in a population-based sample of 1353 subjects, aged 55-74 years (62% response) in Augsburg (Southern Germany) from 1999 to 2001. The cohort was reinvestigated in 2006-2008. Of those individuals without diabetes at baseline, 887 (74%) participated in the follow-up. Ninety-three (10.5%) validated diabetes cases occurred during the follow-up. In logistic regression analyses for model 1, variables were selected from personal characteristics and additional variables were selected from routinely measurable blood parameters (model 2) and from 2-h glucose, adiponectin, insulin and homeostasis model assessment of insulin resistance (HOMA-IR) (model 3).

RESULTS

Age, sex, BMI, parental diabetes, smoking and hypertension were selected for model 1. Model 2 additionally included fasting glucose, HbA(1c) and uric acid. The same variables plus 2-h glucose were selected for model 3. The area under the receiver operating characteristic curve significantly increased from 0.763 (model 1) to 0.844 (model 2) and 0.886 (model 3) (P<0.01). Biomarkers such as adiponectin and insulin did not improve the predictive abilities of models 2 and 3. Cross-validation and bootstrap-corrected model performance indicated high internal validity.

CONCLUSIONS

This longitudinal study in an older population provides models to predict the future risk of Type 2 diabetes. The OGTT, but not biomarkers, improved discrimination of incident diabetes.

Enthesopathies as occupational stress markers: evidence from the upper limb

Enthesopathies--that is, "musculo-skeletal stress markers"--are frequently used to reconstruct past lifestyles and activity patterns. Relatively little attention has been paid in physical anthropology to methodological gaps implicit in this approach: almost all methods previously employed neglect current medical insights into enthesopathies and the distinction between healthy and pathological aspects has been arbitrary. This study presents a new visual method of studying fibrocartilaginous enthesopathies of the upper limb (modified from Villotte: Bull Mém Soc Anthropol Paris n.s. 18 (2006) 65-85), and application of this method to 367 males who died between the 18th and 20th centuries, from four European identified skeletal collections: the Christ Church Spitalfields Collection, the identified skeletal collection of the anthropological museum of the University of Coimbra, and the Sassari and Bologna collections of the museum of Anthropology, University of Bologna. The analysis, using generalized estimating equations to model repeated binary outcome variables, has established a strong link between enthesopathies and physical activity: men with occupations involving heavy manual tasks have significantly (P-value < 0.001) more lesions of the upper limbs than nonmanual and light manual workers. Probability of the presence of an enthesopathy also increases with age and is higher for the right side compared with the left. Our study failed to distinguish significant differences between the collections when adjusted for the other effects. It appears that enthesopathies can be used to reconstruct past lifestyles of populations if physical anthropologists: 1) pay attention to the choice of entheses in their studies and 2) use appropriate methods.

A conditional approach for inference in multivariate age-period-cohort models

Age-period-cohort (APC) models are used to analyse data from disease registers given by age and time. When data are stratified by one further variable, for example geographical location, multivariate APC (MAPC) models can be applied to identify and estimate heterogeneous time trends across the different strata. In such models, outcomes share a set of parameters, typically the age effects, while the remaining parameters may differ across strata. In this article, we propose a conditional approach for inference to directly model relative time trends. We show that in certain situations the conditional approach can handle unmeasured confounding so that relative risks might be estimated with higher precision. Furthermore, we propose an extension for data with more stratification levels. Maximum likelihood estimation is performed using software for multinomial logistic regression. The usage of smoothing splines is suggested to stabilise estimates of relative time trends, if necessary. We apply the methodology to chronic obstructive pulmonary disease mortality data in England & Wales, stratified by three different areas and gender.

Factors associated with whole carcass condemnation rates in provincially-inspected abattoirs in Ontario 2001-2007: implications for food animal syndromic surveillance

BACKGROUND

Ontario provincial abattoirs have the potential to be important sources of syndromic surveillance data for emerging diseases of concern to animal health, public health and food safety. The objectives of this study were to: (1) describe provincially inspected abattoirs processing cattle in Ontario in terms of the number of abattoirs, the number of weeks abattoirs process cattle, geographical distribution, types of whole carcass condemnations reported, and the distance animals are shipped for slaughter; and (2) identify various seasonal, secular, disease and non-disease factors that might bias the results of quantitative methods, such as cluster detection methods, used for food animal syndromic surveillance.

RESULTS

Data were collected from the Ontario Ministry of Agriculture, Food and Rural Affairs and the Ontario Cattlemen's Association regarding whole carcass condemnation rates for cattle animal classes, abattoir compliance ratings, and the monthly sales-yard price for various cattle classes from 2001-2007. To analyze the association between condemnation rates and potential explanatory variables including abattoir characteristics, season, year and commodity price, as well as animal class, negative binomial regression models were fit using generalized estimating equations (GEE) to account for autocorrelation among observations from the same abattoir. Results of the fitted model found animal class, year, season, price, and audit rating are associated with condemnation rates in Ontario abattoirs. In addition, a subset of data was used to estimate the average distance cattle are shipped to Ontario provincial abattoirs. The median distance from the farm to the abattoir was approximately 82 km, and 75% of cattle were shipped less than 100 km.

CONCLUSIONS

The results suggest that secular and seasonal trends, as well as some non-disease factors will need to be corrected for when applying quantitative methods for syndromic surveillance involving these data. This study also demonstrated that animals shipped to Ontario provincial abattoirs come from relatively local farms, which is important when considering the use of spatial surveillance methods for these data.

Microclimate and human factors in the divergent ecology of Aedes aegypti along the Arizona, U.S./Sonora, MX border

This study examined the association of human and environmental factors with the presence of Aedes aegypti, the vector for dengue fever and yellow fever viruses, in a desert region in the southwest United States and northwest Mexico. Sixty-eight sites were longitudinally surveyed along the United States-Mexico border in Tucson, AZ, Nogales, AZ, and Nogales, Sonora during a 3-year period. Aedes aegypti presence or absence at each site was measured three times per year using standard oviposition traps. Maximum and minimum temperature and relative humidity were measured hourly at each site. Field inventories were conducted to measure human housing factors potentially affecting mosquito presence, such as the use of air-conditioning and evaporative coolers, outdoor vegetation cover, and access to piped water. The results showed that Ae. aegypti presence was highly variable across space and time. Aedes aegypti presence was positively associated with highly vegetated areas. Other significant variables included microclimatic differences and access to piped water. This study demonstrates the importance of microclimate and human factors in predicting Ae. aegypti distribution in an arid environment.

The Pennsylvania certified safety committee program: an evaluation of participation and effects on work injury rates

BACKGROUND

Since 1994, Pennsylvania, like several other states, has provided a 5% discount on workers' compensation insurance premiums for firms with a certified joint labor management safety committee. This study explored the factors affecting program participation and evaluated the effect of this program on work injuries.

METHODS

Using Pennsylvania unemployment insurance data (1996-2006), workers' compensation data (1998-2005), and the safety committee audit data (1999-2007), we conducted propensity score matching and regression analysis on the program's impact on injury rates.

RESULTS

Larger firms, firms with higher injury rates, firms in high risk industries, and firms without labor unions were more likely to join the safety committee program and less likely to drop out of the program. The injury rates of participants did not decline more than the rates for non-participants; however, rates at participant firms with good compliance dropped more than the rates at participant firms with poor compliance.

CONCLUSIONS

Firm size and prior injury rates are key predictors of program participation. Firms that complied with the requirement to train their safety committee members did experience reductions in injuries, but non-compliance with that and other requirements was so widespread that no overall impact of the program could be detected.

A Portuguese value set for the SF-6D

OBJECTIVES

The SF-6D is a preference-based measure of health derived from the SF-36 that can be used for cost-effectiveness analysis using cost-per-quality adjusted life-year analysis. This study seeks to estimate a system weight for the SF-6D for Portugal and to compare the results with the UK system weights.

METHODS

A sample of 55 health states defined by the SF-6D has been valued by a representative random sample of the Portuguese population, stratified by sex and age (n = 140), using the Standard Gamble (SG). Several models are estimated at both the individual and aggregate levels for predicting health-state valuations. Models with main effects, with interaction effects and with the constant forced to unity are presented. Random effects (RE) models are estimated using generalized least squares (GLS) regressions. Generalized estimation equations (GEE) are used to estimate RE models with the constant forced to unity. Estimations at the individual level were performed using 630 health-state valuations. Alternative functional forms are considered to account for the skewed distribution of health-state valuations.

RESULTS

The models are analyzed in terms of their coefficients, overall fit, and the ability for predicting the SG-values. The RE models estimated using GLS and through GEE produce significant coefficients, which are robust across model specification. However, there are concerns regarding some inconsistent estimates, and so parsimonious consistent models were estimated. There is evidence of under prediction in some states assigned to poor health. The results are consistent with the UK results.

CONCLUSION

The models estimated provide preference-based quality of life weights for the Portuguese population when health status data have been collected using the SF-36. Although the sample was randomly drowned findings should be treated with caution, given the small sample size, even knowing that they have been estimated at the individual level.

Risk of malaria transmission from fish ponds in the Peruvian Amazon

BACKGROUND

The contribution made by fish ponds (pisciculture) to malaria transmission in the Peruvian Amazon remains to be confirmed. Recent entomological evidence indicates that Anopheles darlingi, the main malaria vector in the region, is frequently found in fish ponds along the Iquitos-Nauta road (Loreto, Peru). The aim of this study was to quantify the effect of fish pond density on malaria occurrence.

METHODS

A retrospective 30-month cohort study was conducted in eight communities along the Iquitos-Nauta road. Malaria incidence was ascertained from malaria registries of the local health post, which consist of data from both active and passive surveillance (247 cases). Fish pond density was measured using an interpreted satellite image and information on potential confounders was collected through interviewer-administered questionnaires.

RESULTS

A total of 1018 individuals from 234 eligible households (90% of the 259 total number of households in the study area) provided complete information on exposures and outcome. Fish pond density was found to be a significant predictor of malaria occurrence (aOR=1.23; 95% CI: 1.09-1.38).

CONCLUSION

The association between fish pond density and malaria suggests that fish ponds contribute to malaria transmission in the region. These results have important implications for the prevention and control of malaria and the development of pisciculture as an important economic activity in Amazonia and beyond.

Contextual and family factors associated with negative assessment of children's health

BACKGROUND

The health and well-being of children are intimately linked to their families' physical, emotional and social circumstances. Evaluation of children's health has most often been based on parental responses. This work investigates whether proxy health, family context and household factors are associated with child's poor health reported by parental figures.

METHODS

Data of 32,688 children of three age-strata (0-5; 6-11; 12-17 years) were obtained from a representative survey in Brazil in 2003. The analyses used generalized estimation equations to examine the association between having a bad health evaluation and the following factors grouped as: children/adolescents characteristics, history of child's health care use, proxy characteristics and family and household factors.

RESULTS

Over 60% of the questionnaires were answered by the child's mother, with no significant difference among age groups. The proportion of children who had their health rated as bad decreased with age and was greater among males in all age groups (9.7%; 7.5%; 6.7% vs. 6.8%; 6.6%; 6.3%). The final model shows that household income per capita is inversely related to child's bad health in all age groups. Additionally, parent/proxy bad self-rated health is strongly and directly associated with child's bad health and is not explained by measures of the child's health or by the proxy's lack of education or a family's low income. The number of medical visits by the child in past year is also inversely associated with bad health.

CONCLUSION

Results reinforce the importance of the household context to child's health and the association between parental figures and child health.

Transformation of abandoned farm fields into coniferous plantations: Is there enough vegetation structure left to maintain winter habitat of snowshoe hares?

Natural forests will likely be unable to sustainably fulfill society needs for wood fibers and intensively managed plantations could be an alternative source of timber in the future. Abandoned farm fields are often targeted for conversion, as they are already disturbed sites; however, they also represent high-quality habitat for species such as snowshoe hares ( Lepus americanus Erxleben 1777), a keystone mammal in the boreal forest. We evaluated the effect of converting abandoned farm fields (n = 22) to conifer plantations (n = 19) on habitat use by snowshoe hares, using pellet counts and snow-tracking surveys. Both survey techniques yielded similar results: winter habitat use by hares is mostly affected by vegetation cover rather than habitat type. In the short term, plantations do not offer less protective cover than the one found in abandoned farm fields. However, upon reaching a certain height (≥7 m), plantations are mechanically pruned and lose their protective quality. Promoting silvicultural techniques that maintain lateral cover beyond a critical threshold (70%) could preserve the quality of hare habitat for an extended proportion of rotation time of the plantation.

Recent cadmium exposure among male partners may affect oocyte fertilization during in vitro fertilization (IVF)

Purpose

We recently reported evidence suggesting associations between urine cadmium concentrations, reflecting long-term exposure, measured in 25 female patients (relative risk = 1.41, P = 0.412) and 15 of their male partners (relative risk = 0.19, P = 0.097) and oocyte fertilization in vitro. Blood cadmium concentrations reflect more recent exposure.

Methods

We here incorporate those measures into our prior data set and employ multivariable log-binomial regression models to generate hypotheses concerning the relative effects of long-term and recent cadmium exposure on oocyte fertilization in vitro.

Results

No association is indicated for blood cadmium from women and oocyte fertilization, adjusted for urine cadmium and creatinine, blood lead and mercury, age, race/ethnicity and cigarette smoking (relative risk = 0.88, P = 0.828). However, we suggest an inverse adjusted association between blood cadmium from men and oocyte fertilization (relative risk = 0.66, P = 0.143).

Conclusions

These results suggest that consideration of long-term and recent exposures are both important for assessing the effect of partner cadmium levels on oocyte fertilization in vitro.

Pediatricians' attitudes and practices on ADHD before and after the development of ADHD pediatric practice guidelines

PURPOSE

The study aims to assess the changes in attitudes and practices about ADHD reported by AAP fellows between 1999 and 2005 during which AAP ADHD guidelines, training, and quality improvement initiatives occurred.

METHOD

The study assesses AAP-initiated surveys that were conducted between 1999 and 2005 and involving a random sample of 1,000 and 1,603 pediatricians, respectively.

RESULTS

The findings reveal that significant, although modest, increases occurred in pediatric practitioners' self-reported adherence to the guidelines. About 81% of respondents reported routine use of formal diagnostic criteria (up from 67%), and 67% of the respondents routinely use ADHD teacher rating scales (compared to 49% in the 1999 survey). Findings further reveal that treatment with stimulant medications was used extensively by pediatricians from both surveys; more pediatricians in the 2005 survey reported use of a second stimulant if the first did not work, and still more reported almost always providing parent training, although the estimated number remained only about a quarter of the total; and greater familiarity with the initiatives predicted better reported adherence to the guidelines.

CONCLUSION

The reported behaviors of practitioners have moved in the direction of greater adherence with the recommended AAP ADHD guidelines, and there was a positive response to, and a greater use of, the materials developed to enhance practice. The authors infer that practice changes may be due to many factors, including AAP guidelines and associated implementation efforts. Changing physician practices needs to be sustained through a continuing process that requires multiple, varying, sustained efforts directed at physicians, other providers, and families.

Mercury exposure, serum antinuclear/antinucleolar antibodies, and serum cytokine levels in mining populations in Amazonian Brazil: a cross-sectional study

Mercury is an immunotoxic substance that has been shown to induce autoimmune disease in rodent models, characterized by lymphoproliferation, overproduction of immunoglobulin (IgG and IgE), and high circulating levels of auto-antibodies directed at antigens located in the nucleus (antinuclear auto-antibodies, or ANA) or the nucleolus (antinucleolar auto-antibodies, or ANoA). We have reported elevated levels of ANA and ANoA in human populations exposed to mercury in artisanal gold mining, though other confounding variables that may also modulate ANA/ANoA levels were not well controlled. The goal of this study is to specifically test whether occupational and environmental conditions (other than mercury exposure) that are associated with artisanal gold mining affect the prevalence of markers of autoimmune dysfunction. We measured ANA, ANoA, and cytokine concentrations in serum and compared results from mercury-exposed artisanal gold miners to those from diamond and emerald miners working under similar conditions and with similar socio-economic status and risks of infectious disease. Mercury-exposed gold miners had higher prevalence of detectable ANA and ANoA and higher titers of ANA and ANoA as compared to diamond and emerald miners with no occupational mercury exposure. Also, mercury-exposed gold miners with detectable ANA or ANoA in serum had significantly higher concentrations of pro-inflammatory cytokines IL-1beta, TNF-alpha, and IFN-gamma in serum as compared to the diamond and emerald miners. This study provides further evidence that mercury exposure may lead to autoimmune dysfunction and systemic inflammation in affected populations.

A longitudinal study of vibration white finger, cold response of digital arteries, and measures of daily vibration exposure

PURPOSE

To investigate prospectively the relation between vibration-induced vascular disorders and measures of daily exposure to hand-transmitted vibration (HTV).

METHODS

Two hundred and forty-nine HTV workers and 138 control men of the same companies participated in a 3-year follow-up study. The diagnosis of vibration induced white finger (VWF) in the HTV workers and that of Raynaud's phenomenon in the controls was based on the medical history, the administration of color charts and the results of a cold test with measurement of finger systolic blood pressures. Vibration magnitudes from the tools were measured as r.m.s acceleration, frequency weighted according to international standard ISO 5349-1, and also unweighted over the frequency range 6.3-1,250 Hz. Daily vibration exposure was expressed in terms of daily exposure duration and frequency-weighted or unweighted r.m.s. acceleration normalized to a reference period of 8 h (Aw(8) or Auw(8), respectively).

RESULTS

The incidence of VWF varied from 5 to 6% in the HTV workers versus 0-1.5% for Raynaud's phenomenon in the controls. After adjusting for potential confounders, Auw(8) gave better predictions of the incidence of VWF and the cold response of the digital arteries over time than Aw(8) or daily exposure duration. These findings were observed in the entire sample of HTV workers, in those with no VWF at the initial investigation, and in those with normal cold test results at baseline.

CONCLUSIONS

The findings of this longitudinal study suggest that a measure of daily vibration exposure calculated from unweighted r.m.s. acceleration over the frequency range 6.3-1,250 Hz performs better for the prediction of vascular disorders in users of vibratory tools than a measure derived from r.m.s. acceleration frequency weighted according to ISO 5349-1. This study provides epidemiological evidence that more weight should be given to intermediate and high-frequency vibration for evaluating the severity of hand-transmitted vibration.

Characterization of intensive care unit acquired hyponatremia and hypernatremia following cardiac surgery

PURPOSE

Although intensive care unit (ICU) acquired sodium disturbances are common in critically ill patients, few studies have examined sodium disturbances in patients following cardiac surgery. The objective of this study was to describe the epidemiology of ICU-acquired hyponatremia and hypernatremia in patients following cardiac surgery.

METHODS

We identified 6,727 adults (> or =18 yr) who were admitted consecutively to a regional cardiovascular intensive care unit (CVICU) from January 1, 2000 to December 31, 2006 and were documented as having normal serum sodium levels (133 to 145 mmol.L(-1)) during the first day of ICU admission. ICU-acquired hyponatremia and hypernatremia were defined as a change in serum sodium concentration to <133 mmol.L(-1) or >145 mmol.L(-1), respectively, following ICU day one.

RESULTS

A first episode of ICU-acquired hyponatremia and hypernatremia developed in 785 (12%) and 242 (4%) patients, respectively, (95% confidence interval [CI] 11-12% and 95% CI 3-4%, respectively), with a respective incidence density of 4.2 and 1.3 patients per 100 days of ICU admission (95% CI 4.0-4.5 and 95% CI 1.2-1.5). The incidence of ICU-acquired sodium disturbances varied according to the patients' demographic and clinical variables for both hyponatremia (age, diabetes, Acute Physiology and Chronic Health Evaluation [APACHE II] score, mechanical ventilation, length of ICU stay, serum glucose level, and serum potassium level) and hypernatremia (APACHE II score, mechanical ventilation, length of hospital stay prior to ICU admission, length of ICU stay, serum glucose level, and serum potassium level). Compared with patients with normal serum sodium levels, hospital mortality was increased in patients with ICU-acquired hyponatremia (1.6% vs 10%, respectively; P < 0.001) and ICU-acquired hypernatremia (1.6% vs 14%, respectively; P < 0.001).

CONCLUSION

ICU-acquired hyponatremia and hypernatremia are common complications in critically ill patients following cardiac surgery. They are associated with patient demographic and clinical characteristics and an increased risk of hospital mortality.

Paraveterinary service use in Nepal's Himalaya

The involvement of paraveterinarians in animal-health delivery can reduce costs and allow expanded service delivery. Our objectives were to describe use of public paraveterinary services offered by junior technicians (JT) in two regions of Nepal, to identify factors associated with JT service use, and to characterize factors that limit JT service use. We used a survey of livestock owners in the Khumbu and Lower Mustang regions of Nepal's Himalaya to examine JT service use. Of 118 questionnaires completed between May 30, 1997 and July 8, 1997, 81 were analyzed for use of JT services to treat livestock: bovids, equids, and small ruminants. Five factors were associated with owners' use of JT services: living <30 min walk from a JT post (OR=12.2); having a positive opinion about JT services (OR=23.6); animals not having disease events that either impaired mobility or affected production or reproduction (OR=5.6), animals died related to a reported disease event (OR=3.2), and the owners' sex (with women being more likely to report use of JT services than men; OR=5.3).

The effect of social networks and social support on mental health services use, following a life event, among the Baltimore Epidemiologic Catchment Area cohort

The study examined the association between life events and mental health services use, accounting for social networks and social support. Main and stress-buffering effects were estimated using longitudinal data from the Baltimore Epidemiologic Catchment Area cohort (1,920 participants in 1993-1996, of whom 1,071 were re-interviewed in 2004-2005). Following a life event, the odds of using general medical services were increased by almost 50% when there was increased social support from spouse/partner (referral function). The odds of using mental health services within general health setup were reduced by 60% when there was increased support from relatives (stress-reduction function). Increased social support from friends and relatives was associated with a 40-60% decreased odds of using specialty psychiatric services after experiencing different life events (stress-reduction function). Overall, social support rather than social networks were more strongly associated with increased mental health service use following a life event. The implications for service delivery and program development are discussed.

Altruistic defence behaviours in aphids

BACKGROUND

Altruistic anti-predatory behaviours pose an evolutionary problem because they are costly to the actor and beneficial to the recipients. Altruistic behaviours can evolve through indirect fitness benefits when directed toward kin. The altruistic nature of anti-predatory behaviours is often difficult to establish because the actor can obtain direct fitness benefits, or the behaviour could result from selfish coercion by others, especially in eusocial animals. Non-eusocial parthenogenetically reproducing aphids form colonies of clone-mates, which are ideal to test the altruistic nature of anti-predatory defence behaviours. Many aphids release cornicle secretions when attacked by natural enemies such as parasitoids. These secretions contain an alarm pheromone that alerts neighbours (clone-mates) of danger, thereby providing indirect fitness benefits to the actor. However, contact with cornicle secretions also hampers an attacker and could provide direct fitness to the actor.

RESULTS

We tested the hypothesis that cornicle secretions are altruistic by assessing direct and indirect fitness consequences of smearing cornicle secretions onto an attacker, and by manipulating the number of clone-mates that could benefit from the behaviour. We observed parasitoids, Aphidius rhopalosiphi, foraging singly in patches of the cereal aphid Sitobion avenae of varied patch size (2, 6, and 12 aphids). Aphids that smeared parasitoids did not benefit from a reduced probability of parasitism, or increase the parasitoids' handling time. Smeared parasitoids, however, spent proportionately more time grooming and less time foraging, which resulted in a decreased host-encounter and oviposition rate within the host patch. In addition, individual smearing rate increased with the number of clone-mates in the colony.

CONCLUSIONS

Cornicle secretions of aphids were altruistic against parasitoids, as they provided no direct fitness benefits to secretion-releasing individuals, only indirect fitness benefits through neighbouring clone-mates. Moreover, the use of cornicle secretions was consistent with their altruistic nature, because the occurrence of this behaviour increased with the size of indirect fitness benefits, the number of clone-mates that can benefit. This study provides evidence for a case of kin-directed altruistic defence outside eusocial animals.

Dose-response analyses using restricted cubic spline functions in public health research

Taking into account a continuous exposure in regression models by using categorization, when non-linear dose-response associations are expected, have been widely criticized. As one alternative, restricted cubic spline (RCS) functions are powerful tools (i) to characterize a dose-response association between a continuous exposure and an outcome, (ii) to visually and/or statistically check the assumption of linearity of the association, and (iii) to minimize residual confounding when adjusting for a continuous exposure. Because their implementation with SAS® software is limited, we developed and present here an SAS macro that (i) creates an RCS function of continuous exposures, (ii) displays graphs showing the dose-response association with 95 per cent confidence interval between one main continuous exposure and an outcome when performing linear, logistic, or Cox models, as well as linear and logistic-generalized estimating equations, and (iii) provides statistical tests for overall and non-linear associations. We illustrate the SAS macro using the third National Health and Nutrition Examination Survey data to investigate adjusted dose-response associations (with different models) between calcium intake and bone mineral density (linear regression), folate intake and hyperhomocysteinemia (logistic regression), and serum high-density lipoprotein cholesterol and cardiovascular mortality (Cox model).

Latent transition models with latent class predictors: attention deficit hyperactivity disorder subtypes and high school marijuana use

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder which is most often diagnosed in childhood with symptoms often persisting into adulthood. Elevated rates of substance use disorders have been evidenced among those with ADHD, but recent research focusing on the relationship between subtypes of ADHD and specific drugs is inconsistent. We propose a latent transition model (LTM) to guide our understanding of how drug use progresses, in particular marijuana use, while accounting for the measurement error that is often found in self-reported substance use data. We extend the LTM to include a latent class predictor to represent empirically derived ADHD subtypes that do not rely on meeting specific diagnostic criteria. We begin by fitting two separate latent class analysis (LCA) models by using second-order estimating equations: a longitudinal LCA model to define stages of marijuana use, and a cross-sectional LCA model to define ADHD subtypes. The LTM model parameters describing the probability of transitioning between the LCA-defined stages of marijuana use and the influence of the LCA-defined ADHD subtypes on these transition rates are then estimated by using a set of first-order estimating equations given the LCA parameter estimates. A robust estimate of the LTM parameter variance that accounts for the variation due to the estimation of the two sets of LCA parameters is proposed. Solving three sets of estimating equations enables us to determine the underlying latent class structures independently of the model for the transition rates and simplifying assumptions about the correlation structure at each stage reduces the computational complexity.

A conditional model of evidence-based decision making

RATIONALE, AIMS AND OBJECTIVES

Efforts to describe how individual treatment decisions are informed by systematic knowledge have been hindered by a standard that gauges the quality of clinical decisions by their adherence to guidelines and evidence-based practices. This paper tests a new contextual standard that gauges the incorporation of knowledge into practice and develops a model of evidence-based decision making. Previous work found that the forecasted outcome of a treatment guideline exerts a highly significant influence on how it is used in making decisions. This study proposed that forecasted outcomes affect the recognition of a treatment scenario, and this recognition triggers distinct contextual decision strategies.

METHODS

Twenty-one volunteers from a psychiatric residency programme responded to 64 case vignettes, 16 in each of the four treatment scenarios. The vignettes represented a fully balanced within-subjects design that included guideline switching criteria and patient-specific factors. For each vignette, participants indicated whether they endorsed the guideline's recommendation.

RESULTS

Clinicians used consistent contextual decision strategies in responding to clearly positive or negative forecasts. When forecasts were more ambiguous or risky, their strategies became complex and relatively inconsistent.

CONCLUSION

The results support a three-step model of evidence-based decision making, in which clinicians recognize a decision scenario, apply a simple contextual strategy, then if necessary engage a more complex strategy to resolve discrepancies between general guidelines and specific cases. The paper concludes by noting study limitations and discussing implications of the model for future research in clinical and shared decision making, training and guideline development.

Changes in weather and the effects on pediatric asthma exacerbations

BACKGROUND

Pediatric asthma exacerbations may correlate with changes in weather, yet this relationship is not well defined.

OBJECTIVE

To determine the effects of fluctuations in climatic factors (temperature, humidity, and barometric pressure) on pediatric asthma exacerbations.

METHODS

A retrospective study was performed at 1 large urban hospital during a 2-year period (January 1, 2004, to December 31, 2005). Children presenting to the emergency department (ED) for an asthma exacerbation were included. Data on climactic factors, pollutants, and aeroallergens were collected daily. The relationship of daily (intraday) or between-day (interday) changes in climactic factors and asthma ED visits was evaluated using time series analysis, controlling for seasonality, air pollution, and aeroallergen exposure. The effects of climactic factors were evaluated on the day of admission (T=0) and up to 5 days before admission (T-5 through T-1).

RESULTS

There were 25,401 asthma ED visits. A 10% intraday increase in humidity on day T-1 or day T-2 was associated with approximately 1 additional ED visit for asthma (P < .001 and P = .01, respectively). Interday changes in humidity from day T - 3 to T-2 were also associated with more ED visits (P < .001). Interday changes in temperature from T-1 to T = 0 increased ED visits, with a 10 degrees F increase being associated with 1.8 additional visits (P = .006). No association was found with changes in barometric pressure.

CONCLUSION

Fluctuations in humidity and temperature, but not barometric pressure, appear to influence ED visits for pediatric asthma. The additional ED visits occur 1 to 2 days after the fluctuation.

Time series analysis of dengue fever and weather in Guangzhou, China

BACKGROUND

Monitoring and predicting dengue incidence facilitates early public health responses to minimize morbidity and mortality. Weather variables are potential predictors of dengue incidence. This study explored the impact of weather variability on the transmission of dengue fever in the subtropical city of Guangzhou, China.

METHODS

Time series Poisson regression analysis was performed using data on monthly weather variables and monthly notified cases of dengue fever in Guangzhou, China for the period of 2001-2006. Estimates of the Poisson model parameters was implemented using the Generalized Estimating Equation (GEE) approach; the quasi-likelihood based information criterion (QICu) was used to select the most parsimonious model.

RESULTS

Two best fitting models, with the smallest QICu values, are selected to characterize the relationship between monthly dengue incidence and weather variables. Minimum temperature and wind velocity are significant predictors of dengue incidence. Further inclusion of minimum humidity in the model provides a better fit.

CONCLUSION

Minimum temperature and minimum humidity, at a lag of one month, are positively associated with dengue incidence in the subtropical city of Guangzhou, China. Wind velocity is inversely associated with dengue incidence of the same month. These findings should be considered in the prediction of future patterns of dengue transmission.

Sequential multiple-assignment randomized trial design of neurobehavioral treatment for patients with metastatic malignant melanoma undergoing high-dose interferon-alpha therapy

BACKGROUND

Interferon-alpha therapy, which is used to treat metastatic malignant melanoma, can cause patients to develop two distinct neurobehavioral symptom complexes: a mood syndrome and a neurovegetative syndrome. Interferon-alpha effects on serotonin metabolism appear to contribute to the mood and anxiety syndrome, while the neurovegetative syndrome appears to be related to interferon-alpha effects on dopamine.

PURPOSE

Our goal is to propose a design for utilizing a sequential, multiple assignment, randomized trial design for patients with malignant melanoma to test the relative efficacy of drugs that target serotonin versus dopamine metabolism during 4 weeks of intravenous, then 8 weeks of subcutaneous, interferon-alpha therapy.

METHODS

Patients will be offered participation in a double-blinded, randomized, controlled, 14-week trial involving two treatment phases. During the first month of intravenous interferon-alpha therapy, we will test the hypotheses that escitalopram will be more effective in reducing depressed mood, anxiety, and irritability, whereas methylphenidate will be more effective in diminishing interferon-alpha-induced neurovegetative symptoms, such as fatigue and psychomotor slowing. During the next 8 weeks of subcutaneous interferon therapy, participants whose symptoms do not improve significantly will be randomized to the alternate agent alone versus escitalopram and methylphenidate together.

RESULTS

We present a prototype for a single-center, sequential, multiple assignment, randomized trial, which seeks to determine the efficacy of sequenced and targeted treatment for the two distinct symptom complexes suffered by patients treated with interferon-alpha.

LIMITATIONS

Because we cannot completely control for external factors, a relevant question is whether or not 'short-term' neuropsychiatric interventions can increase the number of interferon-alpha doses tolerated and improve long-term survival.

CONCLUSIONS

This sequential, multiple assignment, randomized trial proposes a framework for developing optimal treatment strategies; however, additional studies are needed to determine the best strategy for treating or preventing neurobehavioral symptoms induced by the immunotherapy interferon-alpha.

The role of social network and support in mental health service use: findings from the Baltimore ECA study

OBJECTIVE

A significant number of people with mental illness do not use mental health services to receive treatment for their symptoms. This study examined the hypothesis that social network and social support affect mental health service use.

METHODS

Data were from the Baltimore cohort of the Epidemiologic Catchment Area study, a prospective cohort study that gathered data over four time points. This study examined data gathered in 1993-1996 (N=1,920) and 2004-2005 (N=1,071). The study examined indicators of social network and social support in relation to four types of service use (general medical, mental health within general medical, specialty psychiatric, and other human services) with multivariate logistic regression. Examples of other human services include a self-help group or crisis center for help with any psychological problem. Weighted generalized estimating equations were used for the analyses.

RESULTS

Among persons with major depressive disorder, generalized anxiety disorder, panic disorder, or alcohol use disorder in the past year or psychological distress in the past few weeks, general medical service use was reduced when the frequency of contact with relatives or friends occurred less than daily, but it was increased by about 40% when there was a higher than median level of spousal support. In contrast, receiving general medical services for mental health problems was reduced by about 50% when there was a higher than median level of social support from relatives. Specialty psychiatric service use was reduced when there was regular contact with six or more relatives and there was a higher than median level of social support from friends and relatives. None of the social network or social support measures were significantly (p</=.01) associated with use of other human services.

CONCLUSIONS

Increased contact with the social network and higher levels of social support were associated with greater use of general medical services. However, more social support was associated with use of fewer services within the specialty psychiatric sector.

Improved hospital-level risk adjustment for surveillance of healthcare-associated bloodstream infections: a retrospective cohort study

BACKGROUND

To allow direct comparison of bloodstream infection (BSI) rates between hospitals for performance measurement, observed rates need to be risk adjusted according to the types of patients cared for by the hospital. However, attribute data on all individual patients are often unavailable and hospital-level risk adjustment needs to be done using indirect indicator variables of patient case mix, such as hospital level. We aimed to identify medical services associated with high or low BSI rates, and to evaluate the services provided by the hospital as indicators that can be used for more objective hospital-level risk adjustment.

METHODS

From February 2001-December 2007, 1719 monthly BSI counts were available from 18 hospitals in Queensland, Australia. BSI outcomes were stratified into four groups: overall BSI (OBSI), Staphylococcus aureus BSI (STAPH), intravascular device-related S. aureus BSI (IVD-STAPH) and methicillin-resistant S. aureus BSI (MRSA). Twelve services were considered as candidate risk-adjustment variables. For OBSI, STAPH and IVD-STAPH, we developed generalized estimating equation Poisson regression models that accounted for autocorrelation in longitudinal counts. Due to a lack of autocorrelation, a standard logistic regression model was specified for MRSA.

RESULTS

Four risk services were identified for OBSI: AIDS (IRR 2.14, 95% CI 1.20 to 3.82), infectious diseases (IRR 2.72, 95% CI 1.97 to 3.76), oncology (IRR 1.60, 95% CI 1.29 to 1.98) and bone marrow transplants (IRR 1.52, 95% CI 1.14 to 2.03). Four protective services were also found. A similar but smaller group of risk and protective services were found for the other outcomes. Acceptable agreement between observed and fitted values was found for the OBSI and STAPH models but not for the IVD-STAPH and MRSA models. However, the IVD-STAPH and MRSA models successfully discriminated between hospitals with higher and lower BSI rates.

CONCLUSION

The high model goodness-of-fit and the higher frequency of OBSI and STAPH outcomes indicated that hospital-specific risk adjustment based on medical services provided would be useful for these outcomes in Queensland. The low frequency of IVD-STAPH and MRSA outcomes indicated that development of a hospital-level risk score was a more valid method of risk adjustment for these outcomes.

Drug choice, spatial distribution, HIV risk, and HIV prevalence among injection drug users in St. Petersburg, Russia

Background

The HIV epidemic in Russia has been driven by the unsafe injection of drugs, predominantly heroin and the ephedrine derived psychostimulants. Understanding differences in HIV risk behaviors among injectors associated with different substances has important implications for prevention programs.

Methods

We examined behaviors associated with HIV risk among 900 IDUs who inject heroin, psychostimulants, or multiple substances in 2002. Study participants completed screening questionnaires that provided data on sociodemographics, drug use, place of residence and injection- and sex-related HIV risk behaviors. HIV testing was performed and prevalence was modeled using general estimating equation (GEE) analysis. Individuals were clustered by neighborhood and disaggregated into three drug use categories: Heroin Only Users, Stimulant Only Users, and Mixed Drug Users.

Results

Among Heroin Only Users, younger age, front/backloading of syringes, sharing cotton and cookers were all significant predictors of HIV infection. In contrast, sharing needles and rinse water were significant among the Stimulant Only Users. The Mixed Drug Use group was similar to the Heroin Only Users with age, front/back loading, and sharing cotton significantly associated with HIV infection. These differences became apparent only when neighborhood of residence was included in models run using GEE.

Conclusion

The type of drug injected was associated with distinct behavioral risks. Risks specific to Stimulant Only Users appeared related to direct syringe sharing. The risks specific to the other two groups are common to the process of sharing drugs in preparation to injecting. Across the board, IDUs could profit from prevention education that emphasizes both access to clean syringes and preparing and apportioning drug with these clean syringes. However, attention to neighborhood differences might improve the intervention impact for injectors who favor different drugs.

Skeletal forelimb measurements and hoof spread in relation to asymmetry in the bilateral forelimb of horses

REASONS FOR PERFORMING STUDY

Research has highlighted a high frequency of skeletal asymmetries in horses. In addition, research into hoof asymmetries has shown that within a bilateral pair, the hoof with the smaller angle is often subjected to greater loading. There has been limited attention paid to understanding compensatory mechanisms for skeletal asymmetries in the horse; the dynamic structure of the hoof could potentially be acting in a compensatory capacity.

OBJECTIVES

To investigate the relationship between morphometry of forelimb segments and hoof spread and their incidence of asymmetry.

METHODS

Ten bilateral measurements of the hoof and forelimb were taken from 34 leisure horses. The relationship between hoof spread and forelimb segment measurements were analysed using a generalised linear model (GLM).

RESULTS

In relation to left hoof spread, the GLM identified significant negative relationships with left side measurements (third metacarpal length, elbow height), and significant positive relationships with right side measurements (fetlock height, third metacarpal length, elbow height). In relation to right hoof spread, the GLM identified significant negative relationship with left elbow height, and significant positive relationships with right side measurements (fetlock height, point of shoulder). The difference between the number of horses larger to the left or to the right was found to be significant for point of shoulder height (chi2 = 4.8, P < 0.05), and highly significant for heel height (chi2 = 953, P < 0.01) and the third metacarpal length (chi2 = 7.26, P < 0.01).

CONCLUSIONS AND CLINICAL RELEVANCE

The study demonstrated considerable asymmetry in left-right morphometry of the equine limb. The fact that measurements of hoof spread were significantly associated with limb segment measurements could possibly indicate that an interaction exists. Any asymmetry in hoof spread measurements may suggest unequal loading of the limbs, which in turn may contribute to injuries and reduced performance.