195 research outputs found
Social disparities in heart disease risk and survivor bias among autoworkers: an examination based on survival models and g-estimation.
ObjectivesTo examine gender and racial disparities in ischaemic heart disease (IHD) mortality related to metalworking fluid exposures and in the healthy worker survivor effect.MethodsA cohort of white and black men and women autoworkers in the USA was followed from 1941 to 1995 with quantitative exposure to respirable particulate matter from water-based metalworking fluids. Separate analyses used proportional hazards models and g-estimation.ResultsThe HR for IHD among black men was 3.29 (95% CI 1.49 to 7.31) in the highest category of cumulative synthetic fluid exposure. The HR for IHD among white women exposed to soluble fluid reached 2.44 (95% CI 0.96 to 6.22). However, no increased risk was observed among white men until we corrected for the healthy worker survivor effect. Results from g-estimation indicate that if white male cases exposed to soluble or synthetic fluid had been unexposed to that fluid type, then 1.59 and 1.20 years of life would have been saved on average, respectively.ConclusionsWe leveraged the strengths of two different analytic approaches to examine the IHD risks of metalworking fluids. All workers may have the same aetiological risk; however, black and female workers may experience more IHD from water-based metalworking fluid exposure because of a steeper exposure-response or weaker healthy worker survivor effect
Mice Infected with Low-virulence Strains of Toxoplasma gondii Lose their Innate Aversion to Cat Urine, Even after Extensive Parasite Clearance
Toxoplasma gondii chronic infection in rodent secondary hosts has been
reported to lead to a loss of innate, hard-wired fear toward cats, its primary
host. However the generality of this response across T. gondii strains and the
underlying mechanism for this pathogen mediated behavioral change remain
unknown. To begin exploring these questions, we evaluated the effects of
infection with two previously uninvestigated isolates from the three major
North American clonal lineages of T. gondii, Type III and an attenuated strain
of Type I. Using an hour-long open field activity assay optimized for this
purpose, we measured mouse aversion toward predator and non-predator urines. We
show that loss of innate aversion of cat urine is a general trait caused by
infection with any of the three major clonal lineages of parasite.
Surprisingly, we found that infection with the attenuated Type I parasite
results in sustained loss of aversion at times post infection when neither
parasite nor ongoing brain inflammation were detectable. This suggests that T.
gondii-mediated interruption of mouse innate aversion toward cat urine may
occur during early acute infection in a permanent manner, not requiring
persistence of parasitecysts or continuing brain inflammation.Comment: 14 pages, 3 figure
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Estimating Counterfactual Risk Under Hypothetical Interventions in the Presence of Competing Events: Crystalline Silica Exposure and Mortality From 2 Causes of Death.
Exposure to silica has been linked to excess risk of lung cancer and nonmalignant respiratory disease mortality. In this study we estimated risk for both these outcomes in relation to occupational silica exposure as well as the reduction in risk that would result from hypothetical interventions on exposure in a cohort of exposed workers. Analyses were carried out using data from an all-male study population consisting of 2,342 California diatomaceous earth workers regularly exposed to crystalline silica and followed between 1942 and 2011. We estimated subdistribution risk for each event under the natural course and interventions of interest using the parametric g-formula to adjust for healthy-worker survivor bias. The risk ratio for lung cancer mortality, comparing an intervention in which a theoretical maximum exposure limit was set at 0.05 mg/m3 (the current US regulatory limit) with the observed exposure concentrations, was 0.86 (95% confidence interval: 0.63, 1.22). The corresponding risk ratio for nonmalignant respiratory disease mortality was 0.69 (95% confidence interval: 0.52, 0.93). Our findings suggest that risks from both outcomes would have been considerably lower if historical silica exposures in this cohort had not exceeded current regulatory limits
Particle Size Distribution in Aluminum Manufacturing Facilities.
As part of exposure assessment for an ongoing epidemiologic study of heart disease and fine particle exposures in aluminum industry, area particle samples were collected in production facilities to assess instrument reliability and particle size distribution at different process areas. Personal modular impactors (PMI) and Minimicro-orifice uniform deposition impactors (MiniMOUDI) were used. The coefficient of variation (CV) of co-located samples was used to evaluate the reproducibility of the samplers. PM2.5 measured by PMI was compared to PM2.5 calculated from MiniMOUDI data. Mass median aerodynamic diameter (MMAD) and concentrations of sub-micrometer (PM1.0) and quasi-ultrafine (PM0.56) particles were evaluated to characterize particle size distribution. Most of CVs were less than 30%. The slope of the linear regression of PMI_PM2.5 versus MiniMOUDI_PM2.5 was 1.03 mg/m3 per mg/m3 (± 0.05), with correlation coefficient of 0.97 (± 0.01). Particle size distribution varied substantively in smelters, whereas it was less variable in fabrication units with significantly smaller MMADs (arithmetic mean of MMADs: 2.59 μm in smelters vs. 1.31 μm in fabrication units, p = 0.001). Although the total particle concentration was more than two times higher in the smelters than in the fabrication units, the fraction of PM10 which was PM1.0 or PM0.56 was significantly lower in the smelters than in the fabrication units (p < 0.001). Consequently, the concentrations of sub-micrometer and quasi-ultrafine particles were similar in these two types of facilities. It would appear, studies evaluating ultrafine particle exposure in aluminum industry should focus on not only the smelters, but also the fabrication facilities
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Exposure-Lag-Response in Longitudinal Studies: Application of Distributed-Lag Nonlinear Models in an Occupational Cohort.
Prolonged exposures can have complex relationships with health outcomes, as timing, duration, and intensity of exposure are all potentially relevant. Summary measures such as cumulative exposure or average intensity of exposure may not fully capture these relationships. We applied penalized and unpenalized distributed-lag nonlinear models (DLNMs) with flexible exposure-response and lag-response functions in order to examine the association between crystalline silica exposure and mortality from lung cancer and nonmalignant respiratory disease in a cohort study of 2,342 California diatomaceous earth workers followed during 1942-2011. We also assessed associations using simple measures of cumulative exposure assuming linear exposure-response and constant lag-response. Measures of association from DLNMs were generally higher than those from simpler models. Rate ratios from penalized DLNMs corresponding to average daily exposures of 0.4 mg/m3 during lag years 31-50 prior to the age of observed cases were 1.47 (95% confidence interval (CI): 0.92, 2.35) for lung cancer mortality and 1.80 (95% CI: 1.14, 2.85) for nonmalignant respiratory disease mortality. Rate ratios from the simpler models for the same exposure scenario were 1.15 (95% CI: 0.89, 1.48) and 1.23 (95% CI: 1.03, 1.46), respectively. Longitudinal cohort studies of prolonged exposures and chronic health outcomes should explore methods allowing for flexibility and nonlinearities in the exposure-lag-response
Ischemic Heart Disease Incidence in Relation to Fine versus Total Particulate Matter Exposure in a U.S. Aluminum Industry Cohort.
Ischemic heart disease (IHD) has been linked to exposures to airborne particles with an aerodynamic diameter <2.5 μm (PM2.5) in the ambient environment and in occupational settings. Routine industrial exposure monitoring, however, has traditionally focused on total particulate matter (TPM). To assess potential benefits of PM2.5 monitoring, we compared the exposure-response relationships between both PM2.5 and TPM and incidence of IHD in a cohort of active aluminum industry workers. To account for the presence of time varying confounding by health status we applied marginal structural Cox models in a cohort followed with medical claims data for IHD incidence from 1998 to 2012. Analyses were stratified by work process into smelters (n = 6,579) and fabrication (n = 7,432). Binary exposure was defined by the 10th-percentile cut-off from the respective TPM and PM2.5 exposure distributions for each work process. Hazard Ratios (HR) comparing always exposed above the exposure cut-off to always exposed below the cut-off were higher for PM2.5, with HRs of 1.70 (95% confidence interval (CI): 1.11-2.60) and 1.48 (95% CI: 1.02-2.13) in smelters and fabrication, respectively. For TPM, the HRs were 1.25 (95% CI: 0.89-1.77) and 1.25 (95% CI: 0.88-1.77) for smelters and fabrication respectively. Although TPM and PM2.5 were highly correlated in this work environment, results indicate that, consistent with biologic plausibility, PM2.5 is a stronger predictor of IHD risk than TPM. Cardiovascular risk management in the aluminum industry, and other similar work environments, could be better guided by exposure surveillance programs monitoring PM2.5
Incident Ischemic Heart Disease After Long-Term Occupational Exposure to Fine Particulate Matter: Accounting for 2 Forms of Survivor Bias.
Little is known about the heart disease risks associated with occupational, rather than traffic-related, exposure to particulate matter with aerodynamic diameter of 2.5 µm or less (PM2.5). We examined long-term exposure to PM2.5 in cohorts of aluminum smelters and fabrication workers in the United States who were followed for incident ischemic heart disease from 1998 to 2012, and we addressed 2 forms of survivor bias. Left truncation bias was addressed by restricting analyses to the subcohort hired after the start of follow up. Healthy worker survivor bias, which is characterized by time-varying confounding that is affected by prior exposure, was documented only in the smelters and required the use of marginal structural Cox models. When comparing always-exposed participants above the 10th percentile of annual exposure with those below, the hazard ratios were 1.67 (95% confidence interval (CI): 1.11, 2.52) and 3.95 (95% CI: 0.87, 18.00) in the full and restricted subcohorts of smelter workers, respectively. In the fabrication stratum, hazard ratios based on conditional Cox models were 0.98 (95% CI: 0.94, 1.02) and 1.17 (95% CI: 1.00, 1.37) per 1 mg/m(3)-year in the full and restricted subcohorts, respectively. Long-term exposure to occupational PM2.5 was associated with a higher risk of ischemic heart disease among aluminum manufacturing workers, particularly in smelters, after adjustment for survivor bias
Individual-level and plant-level predictors of acute, traumatic occupational injuries in a manufacturing cohort
Objectives: Workplace and contextual factors that may affect risk for worker injury are not well described. This study used results from an employee job satisfaction survey to construct aggregate indicators of the work environment and estimate the relative contribution of those factors to injury rates in a manufacturing cohort. Methods: Principal components analysis was used to construct four plant-level factors from responses to a 32 question survey of the entire workforce, administered in 2006. Multilevel Poisson regression was used to evaluate the relationship between injury rate, individual-level and plant-level risk factors, unionisation and plant type. Results: Plant-level ‘work stress’ (incident rate ratio (IRR)=0.50, 95% CI 0.28 to 0.90) was significant in the multilevel model, indicating the rate of injury for an average individual in that plant was halved (conditional on plant) when job stress decreased by a tertile. ‘Overall satisfaction’, ‘work environment’ and ‘perception of supervisor’ showed the same trend but were not significant. Unionisation was protective (IRR=0.40, 95% CI 0.17 to 0.95) as was any plant type compared with smelter. Conclusions: We demonstrated utility of data from a human resources survey to construct indicators of the work environment. Our research suggests that aspects of the work environment, particularly work stress and unionisation, may have a significant effect on risk for occupational injury, emphasising the need for further multilevel studies. Our work would suggest monitoring of employee perceptions of job stress and the possible inclusion of stress management as a component of risk reduction programmes
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