Diesel exhaust and respiratory dust exposure in miners and chronic obstructive pulmonary disease (COPD) mortality in DEMS II

BACKGROUND

Diesel exhaust and respirable dust exposures in the mining industry have not been studied in depth with respect to non-malignant respiratory disease including chronic obstructive pulmonary disease (COPD), with most available evidence coming from other settings.

OBJECTIVES

To assess the relationship between occupational diesel exhaust and respirable dust exposures and COPD mortality, while addressing issues of survivor bias in exposed miners.

METHODS

The study population consisted of 11,817 male workers from the Diesel Exhaust in Miners Study II, followed from 1947 to 2015, with 279 observed COPD deaths. We fit Cox proportional hazards models for the relationship between respirable elemental carbon (REC) and respirable dust (RD) exposure and COPD mortality. To address healthy worker survivor bias, we leveraged the parametric g-formula to assess effects of hypothetical interventions on both exposures.

RESULTS

Cox models yielded elevated estimates for the associations between average intensity of REC and RD and COPD mortality, with hazard ratios (HR) corresponding to an interquartile range width increase in exposure of 1.46 (95 % confidence interval (CI): 1.12, 1.91) and 1.20 (95 % CI: 0.96, 1.49), respectively for each exposure. HRs for cumulative exposures were negative for both REC and RD. Based on results from the parametric g-formula, the risk ratio (RR) for COPD mortality comparing risk under an intervention eliminating REC to the observed risk was 0.85 (95 % CI: 0.55, 1.06), equivalent to an attributable risk of 15 %. The corresponding RR comparing risk under an intervention eliminating RD to the observed risk was 0.93 (95 % CI: 0.56, 1.31).

CONCLUSIONS

Our findings, based on data from a cohort of nonmetal miners, are suggestive of an increased risk of COPD mortality associated with REC and RD, as well as evidence of survivor bias in this population leading to negative associations between cumulative exposures and COPD mortality in traditional regression analysis.

A Bayesian joint model for compositional mediation effect selection in microbiome data

Analyzing multivariate count data generated by high-throughput sequencing technology in microbiome research studies is challenging due to the high-dimensional and compositional structure of the data and overdispersion. In practice, researchers are often interested in investigating how the microbiome may mediate the relation between an assigned treatment and an observed phenotypic response. Existing approaches designed for compositional mediation analysis are unable to simultaneously determine the presence of direct effects, relative indirect effects, and overall indirect effects, while quantifying their uncertainty. We propose a formulation of a Bayesian joint model for compositional data that allows for the identification, estimation, and uncertainty quantification of various causal estimands in high-dimensional mediation analysis. We conduct simulation studies and compare our method's mediation effects selection performance with existing methods. Finally, we apply our method to a benchmark data set investigating the sub-therapeutic antibiotic treatment effect on body weight in early-life mice.

Associations between prenatal and early-life air pollution exposure and lung function in young children: Exploring influential windows of exposure on lung development

BACKGROUND

Evidence in the literature suggests that air pollution exposures experienced prenatally and early in life can be detrimental to normal lung development, however the specific timing of critical windows during development is not fully understood.

OBJECTIVES

We evaluated air pollution exposures during the prenatal and early-life period in association with lung function at ages 6-9, in an effort to identify potentially influential windows of exposure for lung development.

METHODS

Our study population consisted of 222 children aged 6-9 from the Fresno-Clovis metro area in California with spirometry data collected between May 2015 and May 2017. We used distributed-lag non-linear models to flexibly model the exposure-lag-response for monthly average exposure to fine particulate matter (PM2.5) and ozone (O3) during the prenatal months and first three years of life in association with forced vital capacity (FVC), and forced expiratory volume in the first second (FEV1), adjusted for covariates.

RESULTS

PM2.5 exposure during the prenatal period and the first 3-years of life was associated with lower FVC and FEV1 assessed at ages 6-9. Specifically, an increase from the 5th percentile of the observed monthly average exposure (7.55 μg/m3) to the median observed exposure (12.69 μg/m3) for the duration of the window was associated with 0.42 L lower FVC (95% confidence interval (CI): -0.82, -0.03) and 0.38 L lower FEV1 (95% CI: -0.75, -0.02). The shape of the lag-response indicated that the second half of pregnancy may be a particularly influential window of exposure. Associations for ozone were not as strong and typically CIs included the null.

CONCLUSIONS

Our findings indicate that prenatal and early-life exposures to PM2.5 are associated with decreased lung function later in childhood. Exposures during the latter months of pregnancy may be especially influential.

Associations between Prenatal and Postnatal Exposure to Cannabis with Cognition and Behavior at Age 5 Years: The Healthy Start Study

BACKGROUND

Prenatal exposure to cannabis may influence childhood cognition and behavior, but the epidemiologic evidence is mixed. Even less is known about the potential impact of secondhand exposure to cannabis during early childhood.

OBJECTIVE

This study sought to assess whether prenatal and/or postnatal exposure to cannabis was associated with childhood cognition and behavior.

STUDY DESIGN

This sub-study included a convenience sample of 81 mother-child pairs from a Colorado-based cohort. Seven common cannabinoids (including delta 9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD)) and their metabolites were measured in maternal urine collected mid-gestation and child urine collected at age 5 years. Prenatal and postnatal exposure to cannabis was dichotomized as exposed (detection of any cannabinoid) and not exposed. Generalized linear models examined the associations between prenatal or postnatal exposure to cannabis with the NIH Toolbox and Child Behavior Checklist T-scores at age 5 years.

RESULTS

In this study, 7% (n = 6) of the children had prenatal exposure to cannabis and 12% (n = 10) had postnatal exposure to cannabis, with two children experiencing this exposure at both time points. The most common cannabinoid detected in pregnancy was Δ9-THC, whereas the most common cannabinoid detected in childhood was CBD. Postnatal exposure to cannabis was associated with more aggressive behavior (β: 3.2; 95% CI: 0.5, 5.9), attention deficit/hyperactivity problems (β: 8.0; 95% CI: 2.2, 13.7), and oppositional/defiant behaviors (β: 3.2; 95% CI: 0.2, 6.3), as well as less cognitive flexibility (β: -15.6; 95% CI: -30.0, -1.2) and weaker receptive language (β: -9.7; 95% CI: -19.2, -0.3). By contrast, prenatal exposure to cannabis was associated with fewer internalizing behaviors (mean difference: -10.2; 95% CI: -20.3, -0.2) and fewer somatic complaints (mean difference: -5.2, 95% CI: -9.8, -0.6).

CONCLUSIONS

Our study suggests that postnatal exposure to cannabis is associated with more behavioral and cognitive problems among 5-year-old children, independent of prenatal and postnatal exposure to tobacco. The potential risks of cannabis use (including smoking and vaping) during pregnancy and around young children should be more widely communicated to parents.

The Impact of Job Loss on Self-injury Mortality in a Cohort of Autoworkers: Application of a Novel Causal Approach

BACKGROUND

Recent increases in national rates of suicide and fatal overdose have been linked to a deterioration of economic and social stability. The American auto industry experienced comparable pressures beginning in the 1980s with the emergence of a competitive global market.

METHODS

Using the United Autoworkers-General Motors (GM) cohort as a case study, we examine the impact of employment loss on these self-injury mortality events. For 29,538 autoworkers employed on or after 1 January 1970, we apply incremental propensity score interventions, a novel causal inference approach, to examine how proportional shifts in the odds of leaving active GM employment affect the cumulative incidence of self-injury mortality.

RESULTS

Cumulative incidence of self-injury mortality was 0.87% (255 cases) at the observed odds of leaving active GM employment (δ = 1) over a 45-year period. A 10% decrease in the odds of leaving active GM employment (δ = 0.9) results in an estimated 8% drop in self-injury mortality (234 cases) while a 10% increase (δ = 1.1) results in a 19% increase in self-injury mortality (303 cases).

CONCLUSIONS

These results are consistent with the hypothesis that leaving active employment at GM increases the risk of death due to suicide or drug overdose.

Traffic-related air pollution is associated with glucose dysregulation, blood pressure, and oxidative stress in children

BACKGROUND

Metabolic syndrome increases the risk of cardiovascular disease in adults. Antecedents likely begin in childhood and whether childhood exposure to air pollution plays a contributory role is not well understood.

OBJECTIVES

To assess whether children's exposure to air pollution is associated with markers of risk for metabolic syndrome and oxidative stress, a hypothesized mediator of air pollution-related health effects.

METHODS

We studied 299 children (ages 6-8) living in the Fresno, CA area. At a study center visit, questionnaire and biomarker data were collected. Outcomes included hemoglobin A1c (HbA1c), urinary 8-isoprostane, systolic blood pressure (SBP), and BMI. Individual-level exposure estimates for a set of four pollutants that are constituents of traffic-related air pollution (TRAP) - the sum of 4-, 5-, and 6-ring polycyclic aromatic hydrocarbon compounds (PAH456), NO₂, elemental carbon, and fine particulate matter (PM_2.5) - were modeled at the primary residential location for 1-day lag, and 1-week, 1-month, 3-month, 6-month, and 1-year averages prior to each participant's visit date. Generalized additive models were used to estimate associations between each air pollutant exposure and outcome.

RESULTS

The study population was 53% male, 80% Latinx, 11% Black and largely low-income (6% were White and 3% were Asian/Pacific Islander). HbA1c percentage was associated with longer-term increases in TRAP; for example a 4.42 ng/m³ increase in 6-month average PAH456 was associated with a 0.07% increase (95% CI: 0.01, 0.14) and a 3.62 μg/m³ increase in 6-month average PM_2.5 was associated with a 0.06% increase (95% CI: 0.01, 0.10). The influence of air pollutants on blood pressure was strongest at 3 months; for example, a 6.2 ppb increase in 3-month average NO₂ was associated with a 9.4 mmHg increase in SBP (95% CI: 2.8, 15.9). TRAP concentrations were not significantly associated with anthropometric or adipokine measures. Short-term TRAP exposure averages were significantly associated with creatinine-adjusted urinary 8-isoprostane.

DISCUSSION

Our results suggest that both short- and longer-term estimated individual-level outdoor residential exposures to several traffic-related air pollutants, including ambient PAHs, are associated with biomarkers of risk for metabolic syndrome and oxidative stress in children.

Educational note: addressing special cases of bias that frequently occur in perinatal epidemiology

The epidemiologic study of pregnancy and birth outcomes may be hindered by several unique and challenging issues. Pregnancy is a time-limited period in which severe cohort attrition takes place between conception and birth and adverse outcomes are complex and multi-factorial. Biases span those familiar to epidemiologists: selection, confounding and information biases. Specific challenges include conditioning on potential intermediates, how to treat race/ethnicity, and influential windows of prolonged, seasonal and potentially time-varying exposures. Researchers studying perinatal outcomes should be cognizant of the potential pitfalls due to these factors and address their implications with respect to formulating questions of interest, choice of an appropriate analysis approach and interpretations of findings given assumptions. In this article, we catalogue some of the more important potential sources of bias in perinatal epidemiology that have more recently gained attention in the literature, provide the epidemiologic context behind each issue and propose practices for dealing with each issue to the extent possible.

Native American Ancestry and Air Pollution Interact to Impact Bronchodilator Response in Puerto Rican Children with Asthma

Objective

Asthma is the most common chronic disease in children. Short-acting bronchodilator medications are the most commonly prescribed asthma treatment worldwide, regardless of disease severity. Puerto Rican children display the highest asthma morbidity and mortality of any US population. Alarmingly, Puerto Rican children with asthma display poor bronchodilator drug response (BDR). Reduced BDR may explain, in part, the increased asthma morbidity and mortality observed in Puerto Rican children with asthma. Gene-environment interactions may explain a portion of the heritability of BDR. We aimed to identify gene-environment interactions associated with BDR in Puerto Rican children with asthma.

Setting

Genetic, environmental, and psycho-social data from the Genes-environments and Admixture in Latino Americans (GALA II) case-control study.

Participants

Our discovery dataset consisted of 658 Puerto Rican children with asthma; our replication dataset consisted of 514 Mexican American children with asthma.

Main Outcome Measures

We assessed the association of pairwise interaction models with BDR using ViSEN (Visualization of Statistical Epistasis Networks).

Results

We identified a non-linear interaction between Native American genetic ancestry and air pollution significantly associated with BDR in Puerto Rican children with asthma. This interaction was robust to adjustment for age and sex but was not significantly associated with BDR in our replication population.

Conclusions

Decreased Native American ancestry coupled with increased air pollution exposure was associated with increased BDR in Puerto Rican children with asthma. Our study acknowledges BDR's phenotypic complexity, and emphasizes the importance of integrating social, environmental, and biological data to further our understanding of complex disease.

Associations of Residential Brownness and Greenness with Fasting Glucose in Young Healthy Adults Living in the Desert

Evolutionary psychology theories propose that contact with green, natural environments may benefit physical health, but little comparable evidence exists for brown, natural environments, such as the desert. In this study, we examined the association between "brownness" and "greenness" with fasting glucose among young residents of El Paso, Texas. We defined brownness as the surface not covered by vegetation or impervious land within Euclidian buffers around participants' homes. Fasting glucose along with demographic and behavioral data were obtained from the Nurse Engagement and Wellness Study (n = 517). We found that residential proximity to brownness was not associated with fasting glucose when modeled independently. In contrast, we found that residential greenness was associated with decreased levels of fasting glucose, despite the relatively low levels of greenness within the predominantly desert environment of El Paso. A difference between the top and bottom greenness exposure quartiles within a 250 m buffer was associated with a 3.5 mg/dL decrease in fasting glucose levels (95% confidence interval: -6.2, -0.8). Our results suggest that within the understudied context of the desert, green vegetation may be health promoting to a degree that is similar to other, non-desert locations in the world that have higher baselines levels of green.

Comment on "A global-scale ecological niche model to predict SARS-CoV-2 coronavirus infection rate", author Coro

In this letter we present comments on the article “A global-scale ecological niche model to predict SARS-CoV-2 coronavirus” by Coro published in 2020.

Improved asthma outcomes observed in the vicinity of coal power plant retirement, retrofit, and conversion to natural gas

Coal-fired power plants release substantial air pollution, including over 60% of U.S. sulfur dioxide (SO2) emissions in 2014. Such air pollution may exacerbate asthma however direct studies of health impacts linked to power plant air pollution are rare. Here, we take advantage of a natural experiment in Louisville, Kentucky, where one coal-fired power plant retired and converted to natural gas, and three others installed SO2 emission control systems between 2013 and 2016. Dispersion modeling indicated exposure to SO2 emissions from these power plants decreased after the energy transitions. We used several analysis strategies, including difference-in-differences, first-difference, and interrupted time-series modeling to show that the emissions control installations and plant retirements were associated with reduced asthma disease burden related to ZIP code-level hospitalizations and emergency room visits, and individual-level medication use as measured by digital medication sensors.

Chronic obstructive pulmonary disease mortality: The Diesel Exhaust in Miners Study (DEMS)

BACKGROUND

Miners are highly exposed to diesel exhaust emissions from powered equipment. Although biologically plausible, there is little evidence based on quantitative exposure assessment, that long-term diesel exposure increases risk of chronic obstructive pulmonary disease (COPD). To fill this gap, we examined COPD mortality and diesel exhaust exposure in the Diesel Exhaust in Miners Study (DEMS).

METHODS

We fit Cox models to estimate hazard ratios (HRs) for COPD mortality and cumulative exposure (μg/m³-years) to respirable elemental carbon (REC), a key metric for diesel exhaust exposure. Separate models were fit for ever-underground and surface-only miners to allow for effect modification. Exposure was lagged by 0, 10 and 15 years. In a secondary analysis, we addressed the healthy worker survivor effect by applying the parametric g-formula to handle time-varying confounding affected by prior exposure among ever-underground workers.

RESULTS

Based on 140 cases, the HRs for COPD mortality increased as categories of lagged REC exposure increased for all workers. Among surface-only workers, those in the middle exposure category (0 lag) had a significantly elevated hazard ratio of 2.34 (95% CI: 1.11-4.61) relative to those in the lowest category. Among the ever-underground, that ratio was 1.35, with wide confidence intervals. Using the g-formula, we estimated that the lifetime cumulative risk of COPD mortality would have been reduced from the observed 5.0%-3.1% under a hypothetical intervention where all ever-underground workers were always unexposed.

CONCLUSIONS

Our results suggest long term exposure to diesel exhaust may increase risk of COPD in miners, though power was limited.

Accelerated lung function decline in an aluminium manufacturing industry cohort exposed to PM2.5: an application of the parametric g-formula

OBJECTIVE

Occupational dust exposure has been associated with accelerated lung function decline, which in turn is associated with overall morbidity and mortality. In the current study, we assess potential benefits on lung function of hypothetical interventions that would reduce occupational exposure to fine particulate matter (PM_2.5) while adjusting for the healthy worker survivor effect.

METHODS

Analyses were performed in a cohort of 6485 hourly male workers in an aluminium manufacturing company in the USA, followed between 1996 and 2013. We used the parametric g-formula to assess lung function decline over time under hypothetical interventions while also addressing time-varying confounding by underlying health status, using a composite risk score based on health insurance claims.

RESULTS

A counterfactual scenario envisioning a limit on exposure equivalent to the 10th percentile of the observed exposure distribution of 0.05 mg/m³ was associated with an improvement in forced expiratory volume in one second (FEV₁) equivalent to 37.6 mL (95% CI 13.6 to 61.6) after 10 years of follow-up when compared with the observed. Assuming a linear decrease and (from NHANES reference values), a 20 mL decrease per year for a 1.8 m-tall man as they age, this 37.6 mL FEV₁ loss over 10 years associated with observed exposure would translate to approximately a 19% increase to the already expected loss per year from age alone.

CONCLUSIONS

Our results indicate that occupational PM_2.5 exposure in the aluminium industry accelerates lung function decline over age. Reduction in exposure may mitigate accelerated loss of lung function over time in the industry.

In utero tobacco smoke exposure, DNA methylation, and asthma in Latino children

BACKGROUND

Maternal smoking during pregnancy is a risk factor for chronic disease later in life and has been associated with variability of DNA methylation at specific cytosine-phosphate-guanine (CpG) loci. We assessed the role of DNA methylation as a potential mediator of adverse effects of in utero tobacco smoke exposures on asthma outcomes in Latino children from the US mainland and Puerto Rico.

METHODS

Relationships between self-reported exposure and DNA methylation at CpG loci previously reported to be associated with maternal smoking were assessed in a subsample consisting of 572 children aged 8-21 years (310 cases with asthma, 262 healthy controls), sampled from a larger asthma case-control study. Subsequently, we assessed associations between top loci and asthma-related outcomes, followed by mediation analysis for loci for which associations with outcomes were observed.

RESULTS

Self-reported maternal smoking was associated with a -1.5% (95% confidence interval (CI) = -2.4%, -0.6%) lower methylation at CpG locus cg05575921 on the AHRR gene; a 1% increase in DNA methylation at the same locus resulted in an odds ratio (OR) of 0.90 (95% CI = 0.83, 0.96) for the odds of asthma. The OR for the indirect effect of maternal smoking on asthma mediated through methylation at the cg05575921 locus was 1.18 (95% CI = 1.07, 1.68), compared to the OR for the total effect of exposure in the parent study of 1.48 (95% CI = 1.03, 2.11).

CONCLUSIONS

Our findings suggest potential mediation by DNA methylation in the association between maternal smoking during pregnancy and asthma status.

Acute effects of air pollution on mortality: A 17-year analysis in Kuwait

BACKGROUND

The health burden from exposure to air pollution has been studied in many parts of the world. However, there is limited research on the health effects of air quality in arid areas where sand dust is the primary particulate pollution source.

OBJECTIVE

Study the risk of mortality from exposure to poor air quality days in Kuwait.

METHODS

We conducted a time-series analysis using daily visibility as a measure of particulate pollution and non-accidental total mortality from January 2000 through December 2016. A generalized additive Poisson model was used adjusting for time trends, day of week, and temperature. Low visibility (yes/no), defined as visibility lower than the 25th percentile, was used as an indicator of poor air quality days. Dust storm events were also examined. Finally, we examined these associations after stratifying by gender, age group, and nationality (Kuwaitis/non-Kuwaitis).

RESULTS

There were 73,748 deaths from natural causes in Kuwait during the study period. The rate ratio comparing the mortality rate on low visibility days to high visibility days was 1.01 (95% CI: 0.99-1.03). Similar estimates were observed for dust storms (1.02, 95% CI: 1.00-1.04). Higher and statistically significant estimates were observed among non-Kuwaiti men and non-Kuwaiti adolescents and adults.

CONCLUSION

We observed a higher risk of mortality during days with poor air quality in Kuwait from 2000 through 2016.

Ischemic Heart Disease Mortality and Diesel Exhaust and Respirable Dust Exposure in the Diesel Exhaust in Miners Study

Diesel exhaust is a suggested risk factor for ischemic heart disease (IHD), but evidence from cohorts using quantitative exposure metrics is limited. We examined the impact of respirable elemental carbon (REC), a key surrogate for diesel exhaust, and respirable dust (RD) on IHD mortality, using data from the Diesel Exhaust in Miners Study in the United States. Using data from a cohort of male workers followed from 1948-1968 until 1997, we fitted Cox proportional hazards models to estimate hazard ratios for IHD mortality for cumulative and average intensity of exposure to REC and RD. Segmented linear regression models allowed for nonmonotonicity. Hazard ratios for cumulative and average REC exposure declined relative to the lowest exposure category before increasing to 0.79 and 1.25, respectively, in the highest category. Relative to the category containing the segmented regression change points, hazard ratios for the highest category were 1.69 and 1.54 for cumulative and average REC exposure, respectively. Hazard ratios for RD exposure increased across the full exposure range to 1.33 and 2.69 for cumulative and average RD exposure, respectively. Tests for trend were statistically significant for cumulative REC exposure (above the change point) and for average RD exposure. Our findings suggest excess risk of IHD mortality in relation to increased exposure to REC and RD.

Night and rotational work exposure within the last 12 months and risk of incident hypertension

Objectives Shift work, such as alternating day and nights, causes chronobiologic disruptions which may cause an increase in hypertension risk. However, the relative contributions of the components of shift work ‒ such as shift type (eg, night work) and rotations (ie, switching of shift times; day to night) ‒ on this association are not clear. To address this question, we constructed novel definitions of night work and rotational work and assessed their associations with risk of incident hypertension. Methods A cohort of 2151 workers at eight aluminum manufacturing facilities previously studied for cardiovascular disease was followed from 2003 through 2013 for incident hypertension, as defined by ICD-9 insurance claims codes. Detailed time-registry data was used to classify each worker's history of rotational and night work. The associations between recent rotational work and night work in the last 12 months and incident hypertension were estimated using adjusted Cox proportional hazards models. Results Elevated hazard ratios (HR) were observed for all levels of recent night work (>0-5, >5-50, >50-95, >95-100%) compared with non-night workers, and among all levels of rotational work (<1, 1-10, >10-20, >20-30, and >30%) compared with those working <1% rotational work. In models for considering the combination of night and rotational work, workers with mostly night work and frequent rotations (≥50% night and ≥10% rotation) had the highest risk of hypertension compared to non-night workers [HR 4.00, 95% confidence interval (CI )1.69-9.52]. Conclusions Our results suggest recent night and rotational work may both be associated with higher rates of incident hypertension.

Secondhand smoke exposure and asthma outcomes among African-American and Latino children with asthma

BACKGROUND

Secondhand smoke (SHS) exposures have been linked to asthma-related outcomes but quantitative dose-responses using biomarkers of exposure have not been widely reported.

OBJECTIVES

Assess dose-response relationships between plasma cotinine-determined SHS exposure and asthma outcomes in minority children, a vulnerable population exposed to higher levels of SHS and under-represented in the literature.

METHODS

We performed analyses in 1172 Latino and African-American children with asthma from the mainland USA and Puerto Rico. We used logistic regression to assess relationships of cotinine levels ≥0.05 ng/mL with asthma exacerbations (defined as asthma-related hospitalisations, emergency room visits or oral steroid prescription) in the previous year and asthma control. The shape of dose-response relationships was assessed using a continuous exposure variable in generalised additive logistic models with penalised splines.

RESULTS

The OR for experiencing asthma exacerbations in the previous year for cotinine levels ≥0.05 ng/mL, compared with <0.05 ng/mL, was 1.40 (95% CI 1.03 to 1.89), while the OR for poor asthma control was 1.53 (95% CI 1.12 to 2.13). Analyses for dose-response relationships indicated increasing odds of asthma outcomes related with increasing exposure, even at cotinine levels associated with light SHS exposures.

CONCLUSIONS

Exposure to SHS was associated with higher odds of asthma exacerbations and having poorly controlled asthma with an increasing dose-response even at low levels of exposure. Our results support the conclusion that there are no safe levels of SHS exposures.

Occupational silica exposure and mortality from lung cancer and nonmalignant respiratory disease: G-estimation of structural nested accelerated failure time models

BACKGROUND

Occupational exposure to crystalline silica is known to increase risks of both lung cancer and noninfectious nonmalignant respiratory diseases (NMRD). However, associations between silica exposure and survival times have not been described.

METHODS

In a longitudinal cohort of diatomaceous earth workers exposed to crystalline silica (primarily cristobalite) and followed from 1942 to 2011, we applied g-estimation of structural nested accelerated failure time models to adjust for time-varying confounding that could result in healthy worker survivor bias. A continuous measure of exposure was used in analyses estimating the hypothetical effect of banning exposure to silica on survival time. Since a ban is infeasible, sensitivity analyses examined the hypothetical effects of enforcing various Occupational Exposure Limits.

RESULTS

The estimated median number of years of life lost per worker (for all natural causes) due to silica exposure was 0.48 (95% confidence interval = 0.02, 1.01). For NMRD deaths, the corresponding estimate was 3.22 (0.82, 7.75) and for lung cancer deaths, 2.21 (0.97, 3.56). Cause-specific estimates were sensitive to the use of weights to adjust for competing events. Lung cancer mortality, which tended to occur at younger ages, was an important competing event for NMRD mortality. Sensitivity analyses supported the main results, but with larger estimates, and suggested that a strict limit would be nearly as effective as a complete ban on silica exposure.

CONCLUSIONS

Workplace exposure to crystalline silica in this industry appears to shorten survival times significantly, particularly for those who die of lung cancer or NMRD. More stringent exposure limits are probably warranted.

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.

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.

Lung cancer mortality and exposure to synthetic metalworking fluid and biocides: controlling for the healthy worker survivor effect

OBJECTIVES

Synthetic metalworking fluids (MWFs), widely used to cool and lubricate industrial machining and grinding operations, have been linked with increased risk of several cancers. Estimates of their relation with lung cancer, however, are inconsistent. Controlling for the healthy worker survivor effect, we examined the relations between lung cancer mortality and exposure to synthetic MWF, as well as to biocides added to water-based fluids to control microbial growth, in a cohort of autoworkers. Biocides served as a marker for endotoxin, which has reported antitumour effects, and were hypothesised to be the reason prior studies found reduced lung cancer risk associated with exposure to synthetic fluids.

METHODS

Using the parametric g-formula, we estimated risk ratios (RRs) comparing cumulative lung cancer mortality under no intervention with what would have occurred under hypothetical interventions reducing exposure to zero (ie, a ban) separately for two exposures: synthetic fluids and biocides. We also specified an intervention on synthetic MWF and biocides simultaneously to estimate joint effects.

RESULTS

Under a synthetic MWF ban, we observed decreased lung cancer mortality risk at age 86, RR=0.96 (0.91-1.01), but when we also intervened to ban biocides, the RR increased to 1.03 (0.95-1.11). A biocide-only ban increased lung cancer mortality (RR=1.07 (1.00-1.16)), with slightly larger RR in younger ages.

CONCLUSIONS

Findings suggest a modest positive association for synthetic MWF with lung cancer mortality, contrary to the negative associations reported in earlier studies. Biocide exposure, however, was inversely associated with risk of lung cancer mortality.

Ambient Air Pollution and Asthma-Related Outcomes in Children of Color of the USA: a Scoping Review of Literature Published Between 2013 and 2017

PURPOSE OF REVIEW

Given racial disparities in ambient air pollution (AAP) exposure and asthma risk, this review offers an overview of the literature investigating the ambient air pollution-asthma relationship in children of color between 2013 and 2017.

RECENT FINDINGS

AAP is likely a key contributor to the excess burden of asthma in children of color due to pervasive exposure before birth, at home, and in school. Recent findings suggest that psychosocial stressors may modify the relationship between AAP and asthma. The effect of AAP on asthma in children of color is likely modulated by multiple unique psychosocial stressors and gene-environment interactions. Although children of color are being included in asthma studies, more research is still needed on impacts of specific criteria pollutants throughout the life course. Additionally, future studies should consider historical factors when analyzing current exposure profiles.

The Healthy Worker Survivor Effect: Target Parameters and Target Populations

PURPOSE OF REVIEW

We offer an in-depth discussion of the time-varying confounding and selection bias mechanisms that give rise to the healthy worker survivor effect (HWSE).

RECENT FINDINGS

In this update of an earlier review, we distinguish between the mechanisms collectively known as the HWSE and the statistical bias that can result. This discussion highlights the importance of identifying both the target parameter and the target population for any research question in occupational epidemiology. Target parameters can correspond to hypothetical workplace interventions; we explore whether these target parameters' true values reflect the etiologic effect of an exposure on an outcome or the potential impact of enforcing an exposure limit in a more realistic setting. If a cohort includes workers hired before the start of follow-up, HWSE mechanisms can limit the transportability of the estimates to other target populations. We summarize recent publications that applied g-methods to control for the HWSE, focusing on their target parameters, target populations, and hypothetical interventions.

Air Pollution and Lung Function in Minority Youth with Asthma in the GALA II (Genes-Environments and Admixture in Latino Americans) and SAGE II (Study of African Americans, Asthma, Genes, and Environments) Studies

RATIONALE

Adverse effects of exposures to ambient air pollution on lung function are well documented, but evidence in racial/ethnic minority children is lacking.

OBJECTIVES

To assess the relationship between air pollution and lung function in minority children with asthma and possible modification by global genetic ancestry.

METHODS

The study population consisted of 1,449 Latino and 519 African American children with asthma from five different geographical regions in the mainland United States and Puerto Rico. We examined five pollutants (particulate matter ≤10 μm and ≤2.5 μm in diameter, ozone, nitrogen dioxide, and sulfur dioxide), derived from participant residential history and ambient air monitoring data, and assessed over several time windows. We fit generalized additive models for associations between pollutant exposures and lung function parameters and tested for interaction terms between exposures and genetic ancestry.

MEASUREMENTS AND MAIN RESULTS

A 5 μg/m(3) increase in average lifetime particulate matter less than or equal to 2.5 μm in diameter exposure was associated with a 7.7% decrease in FEV1 (95% confidence interval = -11.8 to -3.5%) in the overall study population. Global genetic ancestry did not appear to significantly modify these associations, but percent African ancestry was a significant predictor of lung function.

CONCLUSIONS

Early-life particulate exposures were associated with reduced lung function in Latino and African American children with asthma. This is the first study to report an association between exposure to particulates and reduced lung function in minority children in which racial/ethnic status was measured by ancestry-informative markers.

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 (PM_2.5) 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 PM_2.5 monitoring, we compared the exposure-response relationships between both PM_2.5 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 10^th-percentile cut-off from the respective TPM and PM_2.5 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 PM_2.5, 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 PM_2.5 were highly correlated in this work environment, results indicate that, consistent with biologic plausibility, PM_2.5 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 PM_2.5.

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.

Marginal structural models in occupational epidemiology: application in a study of ischemic heart disease incidence and PM2.5 in the US aluminum industry

Marginal structural models (MSMs) and inverse probability weighting can be used to estimate risk in a cohort of active workers if there is a time-varying confounder (e.g., health status) affected by prior exposure-a feature of the healthy worker survivor effect. We applied Cox MSMs in a study of incident ischemic heart disease and exposure to particulate matter with aerodynamic diameter of 2.5 μm or less (PM2.5) in a cohort of 12,949 actively employed aluminum workers in the United States. The cohort was stratified by work process into workers in smelting facilities, herein referred to as "smelters" and workers in fabrication facilities, herein referred to as "fabricators." The outcome was assessed by using medical claims data from 1998 to 2012. A composite risk score based on insurance claims was treated as a time-varying measure of health status. Binary PM2.5 exposure was defined by the 10th-percentile cutoff for each work process. Health status was associated with past exposure and predicted the outcome and subsequent exposure in smelters but not in fabricators. In smelters, the Cox MSM hazard ratio comparing those always exposed above the cutoff with those always exposed below the cutoff was 1.98 (95% confidence interval: 1.18, 3.32). In fabricators, the hazard ratio from a traditional Cox model was 1.34 (95% confidence interval: 0.98, 1.83). Results suggest that occupational PM2.5 exposure increases the risk of incident ischemic heart disease in workers in both aluminum smelting and fabrication facilities.

Short-term traffic related exposures and biomarkers of nitro-PAH exposure and oxidative DNA damage

Exposure to vehicle exhaust has been associated with cardiac and respiratory disease, lung cancer, and greater overall mortality. We investigated whether amino- polycyclic aromatic hydrocarbon (amino-PAH) metabolites of nitro-PAHs could be used as biomarkers of these exposures. Pre- and post-shift urine samples were collected at the beginning and end of a work week from 82 male U.S trucking industry workers. We used repeated-measures analysis to examine associations of total 1- and 2-aminonaphthalene (1 & 2-AN) and 1-aminopyrene (1-AP) urinary concentrations with microenvironment exposures to particulate matter (PM_2.5), elemental and organic carbon, and between 1&2-AN and 1-AP with urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG). There was an association between work week mean PM_2.5 levels and post-shift 1 & 2-AN, [141.8 pg/ml increase (95% CI:53.3, 230.2) for each IQR increase (5.54 µg/m³) in PM_2.5,] but no associations with other exposure measures. There was a statistically significant increase in 8-OHdG concentrations with 1 & 2-AN (2.38 µg/mg creatinine (95%CI: 0.19, 4.58) per 242.85 pg/mg creatinine increase in 1 & 2-AN), and suggestive associations with all other exposure measures. Our findings suggest associations between urinary amino-PAHs with vehicle exhaust related PM_2.5 as well as with a biomarker of oxidative DNA damage.

A structural approach to address the healthy-worker survivor effect in occupational cohorts: an application in the trucking industry cohort

BACKGROUND

Occupational cohort studies are often challenged by the Healthy Worker Survivor Effect, which may bias standard methods of analysis. G-estimation of structural failure time models is an approach for reducing this type of bias. Accelerated failure time models have recently been applied in an occupational cohort but cumulative failure time models have not.

METHODS

We used g-estimation of a cumulative failure time model to assess the effect of working as a long-haul driver on ischaemic heart disease mortality in a cohort of 30 448 men employed in the unionised US trucking industry in 1985. Exposure was defined by job title and based on work records. We also applied g-estimation of an accelerated failure time model as a sensitivity analysis and approximated HRs from both models to compare them.

RESULTS

The risk ratio (RR) obtained from the cumulative failure time model, comparing the observed risk under no intervention to the risk had nobody ever been exposed as a long-haul driver, was 1.09 (95% CI 1.02 to 1.16). The RR comparing the risk had everyone been exposed as long-haul driver for 8 years to the risk had nobody ever been exposed was 1.20 (95% CI 1.04 to 1.46). After HR approximations, accelerated failure time model results were similar.

CONCLUSIONS

The cumulative failure time model can effectively control time-varying confounding by Healthy Worker Survivor Effect, and provides an easily interpretable effect estimate. RRs estimated from the cumulative failure time model indicate an elevated ischaemic heart disease mortality risk for long-haul drivers in the US trucking industry.

Traffic-related exposures and biomarkers of systemic inflammation, endothelial activation and oxidative stress: a panel study in the US trucking industry

BACKGROUND

Experimental evidence suggests that inhaled particles from vehicle exhaust have systemic effects on inflammation, endothelial activation and oxidative stress. In the present study we assess the relationships of short-term exposures with inflammatory endothelial activation and oxidative stress biomarker levels in a population of trucking industry workers.

METHODS

Blood and urine samples were collected pre and post-shift, at the beginning and end of a workweek from 67 male non-smoking US trucking industry workers. Concurrent measurements of microenvironment concentrations of elemental and organic carbon (EC & OC), and fine particulate matter (PM2.5) combined with time activity patterns allowed for calculation of individual exposures. Associations between daily and first and last-day average levels of exposures and repeated measures of intercellular and vascular cell adhesion molecule-1 (ICAM-1 & VCAM-1), interleukin 6 (IL-6) and C-reactive protein (CRP) blood levels and urinary 8-Hydroxy-2'-Deoxyguanosine (8-OHdG) were assessed using linear mixed effects models for repeated measures.

RESULTS

There was a statistically significant association between first and last-day average PM2.5 and 8-OHdG (21% increase, 95% CI: 2, 42%) and first and last-day average OC and IL-6 levels (18% increase 95% CI: 1, 37%) per IQR in exposure. There were no significant findings associated with EC or associations suggesting acute cross-shift effects.

CONCLUSION

Our findings suggest associations between weekly average exposures of PM2.5 on markers of oxidative stress and OC on IL-6 levels.

Particulate matter concentrations during desert dust outbreaks and daily mortality in Nicosia, Cyprus

Ambient particulate matter (PM) has been shown to have short- and long-term effects on cardiorespiratory mortality and morbidity. Most of the risk is associated with fine PM (PM(2.5)); however, recent evidence suggests that desert dust outbreaks are major contributors to coarse PM (PM(10-2.5)) and may be associated with adverse health effects. The objective of this study was to investigate the risk of total, cardiovascular and respiratory mortality associated with PM concentrations during desert dust outbreaks. We used a time-series design to investigate the effects of PM(10) on total non-trauma, cardiovascular and respiratory daily mortality in Cyprus, between 1 January 2004 and 31 December 2007. Separate PM(10) effects for non-dust and dust days were fit in generalized additive Poisson models. We found a 2.43% (95% CI: 0.53, 4.37) increase in daily cardiovascular mortality associated with each 10-μg/m(3) increase in PM(10) concentrations on dust days. Associations for total (0.13% increase, 95% CI: -1.03, 1.30) and respiratory mortality (0.79% decrease, 95% CI: -4.69, 3.28) on dust days and all PM(10) and mortality associations on non-dust days were not significant. Although further study of the exact nature of effects across different affected regions during these events is needed, this study suggests adverse cardiovascular effects associated with desert dust events.