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Biomedical subjects

D Loomis

Publications and source records attributed to D Loomis.

At least 19 recordsLinked to original sources
PubMed2005

Relation between ambient air quality and selected birth defects, seven county study, Texas, 1997-2000.

A population-based case-control study investigated the association between maternal exposure to air pollutants, carbon monoxide, nitrogen dioxide, ozone, sulfur dioxide, and particulate matter <10 microm in aerodynamic diameter during weeks 3-8 of pregnancy and the risk of selected cardiac birth defects and oral clefts in livebirths and fetal deaths between 1997 and 2000 in seven Texas counties. Controls were frequency matched to cases on year of birth, vital status, and maternal county of residence at delivery. Stationary monitoring data were used to estimate air pollution exposure. Logistic regression models adjusted for covariates available in the vital record. When the highest quartile of exposure was compared with the lowest, the authors observed positive associations between carbon monoxide and tetralogy of Fallot (odds ratio = 2.04, 95% confidence interval: 1.26, 3.29), particulate matter <10 microm in aerodynamic diameter and isolated atrial septal defects (odds ratio = 2.27, 95% confidence interval: 1.43, 3.60), and sulfur dioxide and isolated ventricular septal defects (odds ratio = 2.16, 95% confidence interval: 1.51, 3.09). There were inverse associations between carbon monoxide and isolated atrial septal defects and between ozone and isolated ventricular septal defects. Evidence that air pollution exposure influences the risk of oral clefts was limited. Suggestive results support a previously reported finding of an association between ozone exposure and pulmonary artery and valve defects.

Air Pollutants↗
PubMed2005

Poisson regression analysis of ungrouped data.

BACKGROUND: Poisson regression is routinely used for analysis of epidemiological data from studies of large occupational cohorts. It is typically implemented as a grouped method of data analysis in which all exposure and covariate information is categorised and person-time and events are tabulated. AIMS: To describe an alternative approach to Poisson regression analysis using single units of person-time without grouping. METHODS: Data for simulated and empirical cohorts were analysed by Poisson regression. In analyses of simulated data, effect estimates derived via Poisson regression without grouping were compared to those obtained under proportional hazards regression. Analyses of empirical data for a cohort of 138 900 electrical workers were used to illustrate how the ungrouped approach may be applied in analyses of actual occupational cohorts. RESULTS: Using simulated data, Poisson regression analyses of ungrouped person-time data yield results equivalent to those obtained via proportional hazards regression: the results of both methods gave unbiased estimates of the "true" association specified for the simulation. Analyses of empirical data confirm that grouped and ungrouped analyses provide identical results when the same models are specified. However, bias may arise when exposure-response trends are estimated via Poisson regression analyses in which exposure scores, such as category means or midpoints, are assigned to grouped data. CONCLUSIONS: Poisson regression analysis of ungrouped person-time data is a useful tool that can avoid bias associated with categorising exposure data and assigning exposure scores, and facilitate direct assessment of the consequences of exposure categorisation and score assignment on regression results.

Adolescent↗
PubMed2005

Incidence of allergy and allergy symptoms among workers exposed to laboratory animals.

BACKGROUND AND AIMS: Few studies have described relations between exposure to laboratory animals and the incidence of laboratory animal allergy (LAA). Studies that have found exposure-response relations have been cross sectional in design or have focused on exposure to rats and mice. This study used longitudinal data collected over a 12 year period to describe the relations between indices of exposure to laboratory animals and the development of LAA and LAA symptoms. METHODS: Data were obtained from questionnaires and serological laboratory results from a dynamic cohort of workers exposed to a variety of laboratory animals in a pharmaceutical manufacturing company. Poisson regression was used to model the incidence rate ratios of species specific and general LAA and LAA symptoms at different levels of exposure. RESULTS: The 12 year incidence rates of LAA symptoms and LAA for all workers were 2.26 (95% CI 1.61 to 2.91) and 1.32 (95% CI 0.76 to 1.87) per 100 person-years, respectively. Higher rate ratios were seen with increasing reported hours of exposure to tasks that required working with animal cages or with many animals at one time. The most common symptoms were related to rhinitis rather than to asthma. CONCLUSIONS: This study suggests that the risk of LAA increases with duration of exposure to animals and work in animal related tasks. Incidence might be reduced by limiting hours per week of exposure to laboratory animals.

Adolescent↗
PubMed2004

Work related injuries in small scale commercial fishing.

OBJECTIVE: To describe the epidemiology of work related injury in a group of small scale, independent commercial fishers. DESIGN: Cross sectional survey (baseline instrument of a prospective cohort study). SETTING AND SUBJECTS: Commercial fishers in eastern North Carolina. RESULTS: A cohort of 219 commercial fishers was established and 215 subjects completed an injury questionnaire. The main types of fishing conducted by the cohort were finfishing (159/215) and crabbing (154/215). Of the 215 fishers, 83 reported that they had suffered an injury event in the previous 12 months, a retrospective recall incidence proportion of 38.6 per 100 workers (95% confidence interval 32.1 to 45.1). The 83 injury events resulted in 94 injuries; 47% were penetrating wounds and 24% were strains/sprains. Half of injuries were to the hand/wrist/digits and 13% were to the back. Of the penetrating wounds, 87% were to the hand/wrist/digits, 32% became infected, and 80% were caused by contact with finfish, shellfish, or other marine animal. Of the strains/sprains, 48% were to the back and 26% were to the shoulder. Seventy percent of strains/sprains were caused by moving heavy objects, mainly either while hauling in nets, pots, or lines or loading/unloading the boat. CONCLUSION: In this group of small scale, independent fishers, the most common reported injuries were penetrating wounds to the hand/wrist/digits from marine animals and strains/sprains to the back while moving heavy objects.

Accidents, Occupational↗
PubMed2004

Deindustrialisation and the long term decline in fatal occupational injuries.

AIMS: To examine the extent to which deindustrialisation accounts for long term trends in occupational injury risk in the United States. METHODS: Rates of fatal unintentional occupational injury were computed using data from death certificates and the population census. Trends were estimated using Poisson regression. Standardisation and regression methods were used to adjust for the potential effect of structural change in the labour market. RESULTS: The fatal occupational injury rate for all industries declined 45% from 1980 to 1996 (RR (rate ratio) 0.55, 95% CI 0.52 to 0.57). Adjustment for structural changes in the workforce shifted the RR to 0.62 (95% CI 0.60 to 0.65). Expanding industries enjoyed more rapid reduction in risk (-3.43% per year, 95% CI -3.62 to -3.24) than those that contracted (-2.65% per year, 95% CI -2.88 to -2.42). CONCLUSIONS: Deindustrialisation contributed to the decline of fatal occupational injury rates in the United States, but explained only 10-15% of the total change.

Accidents, Occupational↗
PubMed2004

The impact of exposure categorisation for grouped analyses of cohort data.

BACKGROUND: Poisson regression is routinely used in occupational and environmental epidemiology. For typical Poisson regression analyses, person-time and events are tabulated by categorising predictor variables that were originally measured on a continuous scale. In order to estimate a dose-response trend, a researcher must decide how to categorise exposures and how to assign scores to exposure groups. AIMS: To investigate the impact on regression results of decisions about exposure categorisation and score assignment. METHODS: Cohort data were generated by Monte Carlo simulation methods. Exposure categories were defined by quintiles or deciles of the exposure distribution. Scores were assigned to exposure groups based on category midpoint and mean exposure levels. Estimated exposure-disease trends derived via Poisson regression were compared to the "true" association specified for the simulation. RESULTS: Under the assumption that exposures conform to a lognormal or exponential distribution, trend estimates tend to be negatively biased when scores are assigned based on category midpoints and positively biased when scores are assigned based on cell specific mean values. The degree of bias was greater when exposure categories were defined by quintiles of the exposure distribution than when categories were defined by deciles of the exposure distribution. CONCLUSIONS: The routine practice of exposure categorisation and score assignment introduces exposure misclassification that may be differential with respect to disease status and, consequently, lead to biased exposure-disease trend estimates. When using the Poisson regression method to evaluate exposure-disease trends, such problems can be minimised (but not necessarily eliminated) by forming relatively refined exposure categories based on percentiles of the exposure distribution among cases, and by assigning scores to exposure categories that reflect person-time weighted mean exposure levels.

Cohort Studies↗
PubMed2004

Ecological associations between asthma prevalence and potential exposure to farming.

Farming and exposure to livestock have been proposed as protective against the development of asthma in children. An ecological study was conducted to examine the support for these relationships in the USA. County-specific aggregate measures were used to examine the relationship between the prevalence of asthma and wheeze in 7th and 8th grade school children (aged 12-14 yrs) and selected measures of potential exposure to farming in the state of North Carolina. Binomial regression models were fitted to quantify these relationships, with adjustments for parental smoking, socioeconomic status, sex and race. Regression coefficients were reported for an increment of one interquartile range (IQR) in each indicator of exposure. The prevalence of asthma showed decreasing trends for most indicators of farm exposure. Regression results suggested that the largest decreases in asthma prevalence were associated with the number of farms (-5.0% per IQR increment), acreage of hay (-7.2% per IQR increment) and beef cattle (-7.8% per IQR increment). The pattern of results was similar for wheezing. In conclusion, the findings of this study are consistent with the hypothesis that certain farm exposures are protective against childhood asthma. Further research with individual-level data is needed to identify the specific protective exposures.

Adolescent↗
PubMed2003

Diversity of trends in occupational injury mortality in the United States, 1980-96.

OBJECTIVES: Although the United States has generally enjoyed declining rates of fatal occupational injury, the rate of decline has not been uniform. To examine the heterogeneity of trends, changes in fatal occupational injury rates from 1980 to 1996 were estimated by occupation, industry, geographic region, and demographic group. METHODS: Deaths due to injury at work during 1980-96 were identified from the US National Traumatic Occupational Fatality database and populations at risk were estimated from the census of population. Mortality rates were computed for unintentional injuries, homicides, and all injuries combined. The annual rate of change was estimated using Poisson regression to model the death rate as a function of time. RESULTS: The estimated average rates for all fatal occupational injuries and for unintentional injuries declined by 3% per year, while the estimated rate of homicide declined <1% per year. The improvement was faster for men (3% per year) than for women (<1% per year) and for younger relative to older workers (7% per year v 2%-3% per year). Trends were also geographically heterogeneous, with the most rapid declines (7%-8% per year) in the South and West. Injury rates for most occupations and industries declined at near the average rate, but some experienced no change or an increase. The rate of homicide also increased in a number of occupations and industries. CONCLUSIONS: Broad downward trends in occupational fatality rates may be explained by several factors, including organized safety efforts, product and process changes, and the ongoing shift of employment toward safer sectors. Disparities in fatal injury trends draw attention to potential opportunities to reduce risk: work settings with increasing injury rates are of particular concern.

Accidents, Occupational↗
PubMed2001

Homicide on the job: workplace and community determinants.

Homicide is the second leading cause of death on the job for workers in the United States. To identify workplace-level predictors of homicide risk, a case-control study of worker killings in North Carolina in 1994-1998 was conducted. Workplaces were the units of analysis: case workplaces (n = 105) were those where a worker was killed during the study period, while controls (n = 210) were a density sample of North Carolina workplaces, matched on time and industry sector. Potential risk and protective factors were assessed in telephone interviews with workplace managers. Associations were measured by the exposure odds ratio and 95% confidence interval, estimated via conditional logistic regression. Characteristics associated with notably higher risk included being at the current location for 2 years or less (odds ratio (OR) = 5.3, 95% confidence interval (CI): 2.2, 12.6), having only one worker (OR = 2.9, 95% CI: 1.2, 7.2), and having night (OR = 4.9, 95% CI: 2.7, 8.8) or Saturday (OR = 4.2, 95% CI: 1.9, 9.2) hours. Workplaces with only male employees (OR = 3.1, 95% CI: 1.5, 6.5) or with African-American or Asian employees were also more likely to experience a killing. While few of the preceding risk factors are directly modifiable through workplace interventions, it is important to identify them before developing or evaluating preventive measures.

Case-Control Studies↗
PubMed2001

Mortality patterns by occupation in a cohort of electric utility workers.

BACKGROUND: Mortality patterns were examined in a United States cohort of 138,905 male electric utility workers from five companies to help interpret previous studies of health effects in this industry. METHODS: Using Poisson regression techniques, internal cohort analyses examined total mortality, cardiovascular disease, and cancer in relation to duration of employment in each of nineteen occupational categories which comprise utility operations. RESULTS: Relative to workers who were never involved in utility operations (e.g., administrative workers), mortality rate ratios among operations workers were higher for total mortality, cardiovascular disease, and total cancer. Lung cancer risk was consistently elevated, whereas increased mortality for other cancers was less consistent. CONCLUSIONS: The results of this study indicate excess risk of total mortality, cardiovascular disease, and some cancers among electric utility workers, which could be related to both occupational and non-occupational risk factors.

Adult↗
PubMed2001

Population-based case-control study of occupational exposure to electromagnetic fields and breast cancer.

PURPOSE: This population-based case-control study examined occupational exposure to electromagnetic fields in relation to female breast cancer incidence among 843 breast cancer cases and 773 controls. METHODS: Exposure was classified based on work in the two longest-held jobs, and indices of cumulative exposure to magnetic fields based on a measurement survey. RESULTS: Female breast cancer was not associated with employment as an office or industrial worker. For the total study population, cumulative exposure over the entire career, and in the past 0-10 and 10-20 years generally showed odds ratios (ORs) close to the null. Moderately elevated risks were found for intermediate but not high levels of cumulative exposure accumulated 20 or more years ago (OR = 1.5; 95% CI = 1.1-2.0). Associations were stronger for premenopausal women (OR = 1.7; 95% CI = 1.1-2.7) in the past 10-20 years, and those with estrogen-receptor positive (ER+) breast tumors (OR = 2.06; 95% CI = 1.1-4.0). No consistent dose-response patterns were observed. CONCLUSIONS: These findings give little support to the hypothesis that electromagnetic fields cause cancer of the female breast.

Adult↗
PubMed2001

Exposure to extremely low frequency magnetic fields among working women and homemakers.

Given concerns with potential health effects of exposure to magnetic fields, the goal of this study was to examine the magnitude and sources of occupational and residential exposure to extremely low frequency (primarily 60 Hz) magnetic fields among women. Exposure to 60 Hz magnetic fields was surveyed among cases and controls recruited for a study of breast cancer in 25 counties in North Carolina. The 273 women who participated wore an integrating personal magnetic-field exposure meter (AMEX 3-D) that measured their time-weighted average (TWA) exposure. A questionnaire was administered to determine the duration and frequency of electric appliance and machinery use. The geometric mean (GM) of the TWA exposure for employed women was 0.138 microT (range 0.022-3.636 microT) and for homemakers 0.113 microT (range 0.022-0.403 microT). Women working in manufacturing and industrial facilities had the highest exposure (GM 0.265 microT, range 0.054-3.436 microT), while nurses and health technicians (GM 0.134 microT, range 0.032-0.285 microT) and teachers and school administrators (GM 0.099 microT, range 0.035-0.673 microT) had the lowest exposures. Job titles, unless very limited in scope and/or environment, self-reported information about equipment use, potential exposure sources, time, and distance were not good predictors of magnetic-field exposure. Furthermore, the results show that occupations previously observed to have increased risk of breast cancer, such as teachers, nurses, administrative support, and housewives, did not have elevated average magnetic field exposures. Therefore, it is questionable whether exposure to power frequency magnetic fields is the cause of the increased breast cancer risk seen in these occupations.

Adult↗
PubMed2000

Selection of controls in injury case-control studies.

PURPOSE: To assist in elucidating principles underlying the design of injury case-control studies.APPROACH: We begin by defining "event" as the sequence of circumstances that place a person at risk of injury (e.g. bicycle crash) and "injury given the event" as the resultant physical damage (e.g. head injury in bicycle crash). We then identify two broad classes of research question: 1) Studies of risk factors for the event, and, 2) Studies of risk factors for injury given the event. The study base for the first type of research question is all persons at risk of the event, while the study base for the second type is all persons who experience the event, and are therefore at risk of injury. It follows that in studies of risk factors for injury given the event, the controls should be a sample of all persons who experience the event. For example, in a study of bicycle helmets and head injuries, a suitable case group would be cyclists treated for head injury following a bicycle crash. The appropriate control group is drawn from the base population of all cyclists who crashed, including those who had no injuries. The control group may be restricted to cyclists who crashed and sought treatment for non-head injury under the assumption that the exposure distribution (prevalence of cycle helmet use) in the crash/no injury group is identical to the exposure distribution in the crash/non-head injury group.CONCLUSIONS: It is over ten years since innovative researchers in Seattle first applied the case-control design to the problem of bicycle crashes. Since then, successive bicycle injury studies at other centers have largely failed to extend and refine the Seattle methodology. A more critical approach to the design of case-control studies is required if we are to continue to advance the field of injury epidemiology.

Journal Article↗
PubMed2000

Occupational bladder cancer mortality among racial and ethnic minorities in 21 states.

BACKGROUND: Occupational bladder cancer mortality among minority racial/ethnic groups is not well described compared to occupational bladder cancer mortality among non-minority males in the United States. METHODS: Race/ethnicity- and sex-specific bladder cancer mortality (1985-1992) of workers employed in 21 states was examined using a proportionate mortality study design. Mortality of specific racial/ethnic/occupational groups was compared separately with workers in the specific occupation and with members of the specific racial/ethnic group. RESULTS: This study identified elevated bladder cancer mortality among African American males and females and Latino males in several occupational groups with exposure to suspected bladder carcinogens as well as among Asian males in sales (PMR = 2. 13) and Asian females in the personal services industry (PMR = 5.25; CI: 1.64-16.75). CONCLUSIONS: Surveillance of occupational cancer risks among racial/ethnic minorities using regularly available death certificate data is facilitated when states code both usual occupation/industry and race/ethnicity.

Confidence Intervals↗