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Exposure Data (exposure + data)

Distribution by Scientific Domains

Medical Sciences	50%
Life Sciences	31%
Mathematics and Statistics	18%

Selected Abstracts

A Note on Comparing Exposure Data to a Regulatory Limit in the Presence of Unexposed and a Limit of Detection

BIOMETRICAL JOURNAL, Issue 6 2005
Haitao Chu
Abstract In some occupational health studies, observations occur in both exposed and unexposed individuals. If the levels of all exposed individuals have been detected, a two-part zero-inflated log-normal model is usually recommended, which assumes that the data has a probability mass at zero for unexposed individuals and a continuous response for values greater than zero for exposed individuals. However, many quantitative exposure measurements are subject to left censoring due to values falling below assay detection limits. A zero-inflated log-normal mixture model is suggested in this situation since unexposed zeros are not distinguishable from those exposed with values below detection limits. In the context of this mixture distribution, the information contributed by values falling below a fixed detection limit is used only to estimate the probability of unexposed. We consider sample size and statistical power calculation when comparing the median of exposed measurements to a regulatory limit. We calculate the required sample size for the data presented in a recent paper comparing the benzene TWA exposure data to a regulatory occupational exposure limit. A simulation study is conducted to investigate the performance of the proposed sample size calculation methods. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Nutrient intakes in women and congenital diaphragmatic hernia in their offspring,

BIRTH DEFECTS RESEARCH, Issue 3 2008
Wei Yang
Abstract BACKGROUND: Congenital diaphragmatic hernia (CDH) is a severe birth defect where there is an opening in the diaphragm through which a portion of the abdominal contents protrudes into the thoracic cavity. The etiologies of CDH remain unknown, although experimental animal data suggest dietary factors might play a role. This study examined whether maternal nutrient intakes were associated with delivering infants with CDH. METHODS: We analyzed infants with isolated CDH who were born from 1997 to 2003 and recruited into the National Birth Defects Prevention Study (NBDPS), a multisite, population-based case-control study. Exposure data were obtained from telephone interviews, which were completed within 24 months after delivery, and were available for 377 case mothers and 5,008 control mothers. A food frequency questionnaire was used to derive nutrient intakes during the year before pregnancy. RESULTS: A crude OR of 0.6 (95% CI: 0.3,1.0) was observed for higher intake of choline. Elevated ORs (1.4 to 1.7) were found for lower intakes of choline, cysteine, methionine, and protein. Among women who took vitamin supplements, higher intakes of B vitamins (i.e., folate, vitamin B1, B2, B6, and B12), minerals (i.e., calcium, iron, magnesium, and zinc), and vitamin E were inversely associated with CDH (ORs from 0.7,0.3). Moreover, among women who did not take vitamin supplements, lower intakes of calcium, retinol, selenium, vitamin B12, and vitamin E had positive associations with CDH (ORs from 1.4 to 2.1). CONCLUSIONS: Our observations contribute to a limited body of evidence suggesting a woman's periconceptional diet might be associated with CDH in her offspring. Birth Defects Research (Part A), 2008. © 2007 Wiley-Liss, Inc. [source]

Supplementary oxygen and risk of childhood lymphatic leukaemia

ACTA PAEDIATRICA, Issue 12 2002
E Naumburg
Aim: Childhood leukaemia has been linked to several factors, such as asphyxia and birthweight, which in turn are related to newborn resuscitation. Based on the findings from a previous study a population-based case-control study was performed to investigate the association between childhood leukaemia and exposure to supplementary oxygen and other birth-related factors. Methods: Children born in Sweden and diagnosed with lymphatic leukaemia between 1973 and 1989 (578 cases) were individually matched by gender and date of birth to a randomly selected control. Children with Down's syndrome were excluded. Exposure data were blindly gathered from antenatal, obstetric and other standardized medical records. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated by conditional logistic regression. Results: Resuscitation with 100% oxygen with a facemask and bag immediately postpartum was significantly associated with an increased risk of childhood lymphatic leukaemia (OR = 2.57, 95% CI 1.21,6.82). The oxygen-related risk further increased if the manual ventilation lasted for 3 min or more (OR = 3.54, 95% CI 1.16,10.80). Low Apgar scores at 1 and 5 min were associated with a non-significantly increased risk of lymphatic leukaemia. There were no associations between lymphatic leukaemia and supplementary oxygen later in the neonatal period or other birth-related factors. Conclusion: Resuscitation with 100% oxygen immediately postpartum is associated with childhood lymphatic leukaemia, but further studies are warranted to confirm the findings. [source]

Methodological issues in the epidemiological study of the teratogenicity of drugs

CONGENITAL ANOMALIES, Issue 2 2005
Bengt A.J. Källén
ABSTRACT The review presented here discusses and exemplifies problems in epidemiological studies of drug teratogenesis according to methodology: case,control studies, cohort studies, or total population studies. Sources of errors and the possibility of confounding are underlined. The review stresses the caution with which conclusions have to be drawn when exposure data are retrospective or other possible bias exists. It also stresses the problem with the multiple testing situation that is usually present in the studies. It is therefore difficult to draw any firm conclusion from single studies and still more difficult to draw conclusions on causality. As randomized studies are in most cases out of the question, one has to rely on the type of studies which can be made, but the interpretation of the results should be cautious. The ideal study, next to a randomized one, is a large prospective study with detailed exposure information and detailed and unbiased outcome data. Even so, such a study can mainly be used for identifying possible associations which have to be verified or rejected in new studies. Nearly every finding of a risk increase, if not extremely strong, should only be regarded as a tentative signal to be tested in independent studies. [source]

Uncertainty analysis of single-concentration exposure data for risk assessment,introducing the species effect distribution approach

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2006
Janeck J. Scott-fordsmand
Abstract In recent years, the inclusion of uncertainty analysis in risk assessment has been much debated. One pertinent issue is the translation of the effects observed with a limited number of test species to a general protection level for most or all species present in the environment. In a number of cases, toxicity data may consist of data from tests employing only a control and one treatment. Given that more species (or processes) have been tested with the same treatment, the treatment can be considered as fixed, and the effect level of the individual species (or processes) can be considered as variable. The distribution of effects can be viewed as a species effect distribution for that treatment. The distribution will represent all organisms and may be used to predict the maximum impact on any fraction of all organisms (e.g., 95% of all species). Hence, it is possible to predict the maximum effect level, with a selected certainty, for a given fraction of all species. [source]

The teratogenic risk of antiepileptic drug polytherapy

EPILEPSIA, Issue 5 2010
Frank J. E. Vajda
Summary Purpose:, To compare the risks of fetal malformation during pregnancy associated with antiepileptic drug (AED) polytherapy and monotherapy. Methods:, Statistical analysis of malformation rate and antiepileptic drug exposure data from the Australian Register of Antiepileptic Drugs in Pregnancy, and from the literature. Results:, The calculated relative risk (RR) value for AED polytherapy compared with monotherapy was below 1.0 in only 3 of 14 literature publications. In the register, at 1 year postnatally there were fetal malformations in 5.32% of 282 AED polytherapy pregnancies, and in 7.84% of 791 AED monotherapy pregnancies, an RR of 0.68 [95% confidence interval (CI) 0.39,1.17). For pregnancies exposed to valproate, the RR of fetal malformation (0.39, 95% CI 0.20,0.89) was lower in polytherapy (7.26%) than in monotherapy (17.9%); the difference did not depend on valproate dosage. The RR values for fetal malformation were not significantly different for AED polytherapy and monotherapy when valproate was not involved. Logistic regression suggested that coadministration of lamotrigine may have reduced the malformation risk from valproate. Discussion:, The fetal hazard of AED polytherapy relative to monotherapy may depend more on the degree of exposure to valproate than on the fact of polytherapy per se. Coadministration with lamotrigine may lower the fetal risk of valproate therapy. [source]

The influence of sociodemographic characteristics on agreement between self-reports and expert exposure assessments,

AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 10 2010
Grace Sembajwe ScD
Abstract Background Often in exposure assessment for epidemiology, there are no highly accurate exposure data and different measurement methods are considered. The objective of this study was to use various statistical techniques to explore agreement between individual reports and expert ratings of workplace exposures in several industries and investigate the sociodemographic influences on this agreement. Methods A cohort of 1,282 employees at 4 industries/14 worksites answered questions on workplace physical, chemical, and psychosocial exposures over the past 12 months. Occupational hygienists constructed job exposure matrices (JEMs) based on worksite walkthrough exposure evaluations. Worker self-reports were compared with the JEMs using multivariable analyses to explore discord. Results There was poor agreement between the self-reported and expert exposure assessments, but there was evidence that agreement was modified by sociodemographic characteristics. Several characteristics including gender, age, race/ethnicity, hourly wage and nativity strongly affected the degree of discord between self-reports and expert raters across a wide array of different exposures. Conclusions Agreement between exposure assessment tools may be affected by sociodemographic characteristics. This study is cross-sectional and therefore, a snapshot of potential exposures in the workplace. Nevertheless, future studies should take into account the social contexts within which workplace exposures occur. Am. J. Ind. Med. 53:1019,1031, 2010. © 2010 Wiley-Liss, Inc. [source]

Developments in asbestos cancer risk assessment,

AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 11 2009
Michael A. Silverstein MD
Abstract Background Efforts have been made for 25 years to develop asbestos risk assessments that provide valid information about workplace and community cancer risks. Mathematical models have been applied to a group of workplace epidemiology studies to describe the relationships between exposure and risk. EPA's most recent proposed method was presented at a public meeting in July 2008. Methods Risk assessments prepared by USEPA, OSHA, and NIOSH since 1972 were reviewed, along with related literature. Results and Conclusions None of the efforts to use statistical models to characterize relative cancer potencies for asbestos fiber types and sizes have been able to overcome limitations of the exposure data. Resulting uncertainties have been so great that these estimates should not be used to drive occupational and environmental health policy. The EPA has now rejected and discontinued work on its proposed methods for estimating potency factors. Future efforts will require new methods and more precise and reliable exposure assessments. However, while there may be genuine need for such work, a more pressing priority with regard to the six regulated forms of asbestos and other asbestiform fibers is to ban their production and use. Am. J. Ind. Med. 52:850,858, 2009. © 2009 Wiley-Liss, Inc. [source]

Lung function decrease in relation to pneumoconiosis and exposure to quartz-containing dust in construction workers

AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 6 2003
Evelyn Tjoe-Nij MSc
Abstract Background Prevalence of exposure related respiratory symptoms and decreases in lung function are unknown among quartz dust exposed construction workers. Methods In a cross-sectional study (n,=,1,335), the occurrence of respiratory symptoms, was recorded and spirometric lung function was measured. Results were associated with exposure data and presence of radiographic abnormalities and compared with a reference population. Results Pneumoconiosis (profusion category 1/1 or greater) was associated with increased risks of FEV1 and FVC values in the lowest 5% group, and with group-based decreases of 270 ml/s and 180 ml, respectively. Average lung function of construction workers was somewhat lower compared to a Dutch reference population. Lung function was not associated with exposure, except for a reduction in FVC of 5 ml per year for those with higher exposure. Conclusions In quartz dust exposed construction workers obstructive and restrictive lung function loss was detected. Am. J. Ind. Med. 43:574,583, 2003. © 2003 Wiley-Liss, Inc. [source]

Epidemiology of pleural mesothelioma in a population with non-occupational asbestos exposure

RESPIROLOGY, Issue 1 2008
Muzaffer METINTAS
Background and objective: This study describes the epidemiology of malignant pleural mesothelioma (MPM) in a rural population with environmental asbestos exposure. Methods: Patients with diagnosed MPM were recruited and their relevant demographic and exposure data were analysed. Results: A total of 131 patients with MPM (59 men, 72 women) were studied. The patients' mean age was 57.8 years and the mean exposure duration was 28.9 years. The cumulative fibre count of the villagers ranged from 0.19 to 14.61 fibre/mL-years. Of the 131 patients, 85 had epithelial cell type, 20 had mixed, and eight had sarcomatous pleural mesothelioma. No significant relationship was found between asbestos fibre type and age, exposure period, or cellular type of MPM; similarly, no significant relationship could be found between the cellular type and age or exposure period. Patients with sarcomatous mesotheliomas were considerably older. Only five of 131 (3.8%) patients had a family history of mesothelioma. Conclusions: Environmental exposure to asbestos begins at birth and this may be important in the age of disease onset, if a threshold model for cancer initiation is operative. Both men and women had an excess risk of mesothelioma. Given that a family history of MPM was not common in this relatively homogenous patient group, a genetic predisposition to mesothelioma appears unlikely. [source]

The Nordic Countries as a Cohort for Pharmacoepidemiological Research

BASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 2 2010
Kari Furu
Many population-based health registries were established in the 1960s, with use of unique personal identifiers facilitating linkage between registries. In recent years, each country has established a national database to track prescription drugs dispensed to individuals in ambulatory care. The objectives were to present an overview of the prescription databases established in the Nordic countries, as well as to elaborate on their unique potential for record linkage and cross-national comparison of drug utilization. Five Nordic countries collect drug exposure data based on drugs dispensed at pharmacies and have the potential to link these data to health outcomes. The databases together cover 25 million inhabitants (Denmark: 5.5 million; Finland: 5.3 million; Iceland: 0.3 million; Norway: 4.8 million; and Sweden: 9.2 million). In 2007, the registries encompassed 17 million prescription drug users (68% of the total population). We provide examples of how these databases have been used for descriptive drug utilization studies and analytical pharmacoepidemiological studies linking drug exposure to other health registries. Comparisons are facilitated by many similarities among the databases, including data source, content, coverage and methods used for drug utilization studies and record linkage. There are, however, some differences in coding systems and validity, as well as in some access and technical issues. To perform cross-national pharmacoepidemiological studies, resources, networks and time are needed, as well as methods for pooling data. Interpretation of results needs to account for inter-country heterogeneity and the possibility of spurious relationships. The Nordic countries have a unique potential for collaborative high-quality cross-national pharmacoepidemiological studies with large populations. This research may assist in resolving safety issues of international interest, thus minimizing the risk of either over-reacting on possible signals or underestimating drug safety issues. [source]

Personal exposure to mobile communication networks and well-being in children,A statistical analysis based on a functional approach

BIOELECTROMAGNETICS, Issue 4 2009
Anja Kühnlein
Abstract The MobilEe-study was the first cross-sectional population-based study to investigate possible health effects of mobile communication networks on children using personal dosimetry. Exposure was assessed every second resulting in 86,400 measurements over 24 h for each participant. Therefore, a functional approach to analyze the exposure data was considered appropriate. The aim was to categorize exposure taking into account the course of the measurements over 24 h. The analyses were based on the 480 maxima of each 3 min time interval. Exposure was classified using a nonparametric functional method. Heterogeneity of a sample of functional data was assessed by comparing the functional mode and mean of the distribution of a functional variable. The partition was built within a descending hierarchical method. The resulting exposure groups were compared with categories derived from a standard method, which used the average exposure over 24 h and set the cut-off at the 90th percentile. The functional classification resulted in a splitting of the exposure data into two groups. Plots of the mean curves showed that the groups could be interpreted as children with "low exposure" (88%) and "higher exposure" (12%). These groups were comparable with categories of the standard method. No association between the categorized exposure and well-being was observed in logistic regression models. The functional classification approach yielded a plausible partition of the exposure data. The comparability with the standard approach might be due to the data structure and should not be generalized to other exposures. Bioelectromagnetics 30:261,269, 2009. © 2009 Wiley-Liss, Inc. [source]

Occupational exposures to high frequency electromagnetic fields in the intermediate range (,>300 Hz,10 MHz)

BIOELECTROMAGNETICS, Issue 8 2002
Birgitta Floderus
Abstract The aim of this study was to identify work situations with electromagnetic fields of 300 Hz,10 MHz and to characterize the occupational exposure. Work place investigations included descriptions of the work environment and physical measurements. We estimated electric (E) and magnetic (H) fields by spot measurements in air, by logged exposure data, and when possible, we recorded induced currents in limbs. The instruments used were Wandel and Golterman EFA-3, NARDA 8718, Holaday HI-3702. The exposure sources comprised five induction furnaces, seven induction heaters, one surface treatment equipment, four units of electronic article surveillance (EAS), and medical devices for surgery and muscle stimulation. The induction furnaces operated at 480 Hz,7 kHz, and the maximum values of logged data varied between 512,2093 V/m (E field) and 10.5,87.3 A/m (H field). The induction heaters (3.8 kHz,1.25 MHz) also showed high maximum exposure values of both E and H fields. Three EAS units, an electromagnetic plate at a library, a luggage control unit, and an antitheft gate, showed E fields reaching 658,1069 V/m. The H fields were comparatively lower, except for the antitheft gate (5 and 7.5 kHz) showing a maximum value of 27.2 A/m (recorded during repair). Induced currents of 5,13 mA were measured for the medical devices. The study improves the basis for an exposure assessment for epidemiological studies of long term effects of exposures to high frequency electromagnetic fields. Bioelectromagnetics 23:568,577, 2002. © 2002 Wiley-Liss, Inc. [source]

A Note on Comparing Exposure Data to a Regulatory Limit in the Presence of Unexposed and a Limit of Detection

Analysis of Matched Case,Control Data in Presence of Nonignorable Missing Exposure

BIOMETRICS, Issue 1 2008
Samiran Sinha
Summary. The present article deals with informative missing (IM) exposure data in matched case,control studies. When the missingness mechanism depends on the unobserved exposure values, modeling the missing data mechanism is inevitable. Therefore, a full likelihood-based approach for handling IM data has been proposed by positing a model for selection probability, and a parametric model for the partially missing exposure variable among the control population along with a disease risk model. We develop an EM algorithm to estimate the model parameters. Three special cases: (a) binary exposure variable, (b) normally distributed exposure variable, and (c) lognormally distributed exposure variable are discussed in detail. The method is illustrated by analyzing a real matched case,control data with missing exposure variable. The performance of the proposed method is evaluated through simulation studies, and the robustness of the proposed method for violation of different types of model assumptions has been considered. [source]

The utility of mixed-effects covariate analysis in rapid selection of doses in pediatric subjects: A case study with fexofenadine hydrochloride

BIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 9 2004
Rajesh Krishna
Abstract Fexofenadine hydrochloride is a non-sedating antihistamine that is used in the treatment of symptoms associated with seasonal allergic rhinitis and chronic idiopathic urticaria. A pooled analysis of pharmacokinetic data from children 6 months to 12 years of age and adults was conducted to identify the dose(s) in children that produce exposures comparable to those in adults for the treatment of seasonal allergic rhinitis. The pharmacokinetic parameter database included peak and overall exposure data from 269 treatment exposures from 136 adult subjects, and 90 treatment exposures from 77 pediatric allergic rhinitis patients. The data were pooled and analysed using NONMEM software, version 5.0. A covariate model based on body weight and age and a power function model based on body weight were identified as appropriate models to describe the variability in fexofenadine oral clearance and peak concentration, respectively. Individual oral clearance estimates were on average 44%, 36% and 61% lower in children 6 to 12 years (n = 14), 2 to 5 years (n = 21), and 6 months to 2 years (n = 42), respectively, compared with adults. Trial simulations (n = 100) were carried out based on the final pharmacostatistical models and parameter estimates to identify the appropriate dose(s) in children relative to the marketed dose of 60 mg fexofenadine hydrochloride in adults. The trials were designed as crossover studies in 18 subjects comprising various potential dosing regimens with and without weight stratification. Pharmacokinetic parameter variability was assumed to have a log-normal distribution. Individual weights and ages were simulated using mean (SD) estimates derived from the studies used in this analysis and proportional measurement/model mis-specification errors derived from the analysis were incorporated into the simulation. The results indicated that a 30 mg dose of fexofenadine hydrochloride administered to children 1 to 12 years of age and weighing >10.5 kg and a 15 mg dose administered to children 6 months and older and weighing ,10.5 kg produces exposures similar to those seen with the 60 mg dose in adults. Copyright © 2004 John Wiley & Sons, Ltd. [source]