Occupational and Environmental Medicine : Recent

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Trends in participation rates in case-control studies of occupational risk factors 1991-2017

Objective
Declining participation has been observed in previous epidemiological studies, could occupational risk factor epidemiology be particularly vulnerable to this trend? The objective of this study was to assess trends of participation rates in occupational case-control studies.

Methods
Five prominent occupational and epidemiological journals were pre-selected and all articles published between 1991 and 2017 were screened for case-control studies of occupational risk factors for chronic disease outcomes. The primary independent variable was median year of data collection, while the primary outcome variable was reported participation rate. We conducted linear regression, adjusting for study characteristics that included study gender mix, location of recruitment, disease outcome, and data collection method.

Results
A total of 180 studies published in the five journals were included in the final analysis. The mean participation was higher for cases (78.9%) than for controls (71.5%). In linear regression, a significant trend of decreasing participation was observed for both cases with a percent change of –0.50 per year (95% CI –0.75 to –0.25) for cases and a percent change of –0.95 per year (95% CI –1.23 to –0.67) for controls. After adjustment for study gender mix, location, disease outcome, and data collection method, the trend remained statistically significant for both case and control groups.

Conclusion
Declining participation rates in case-control studies of occupational risk factors may reflect an overall decline of participation in population-based samples. Lower participation rates introduce the potential for bias and may deter future population-based studies of occupational risk factors.

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http://oem.bmj.com/cgi/content/short/77/10/659?rss=1

Psychological impact of quarantine on healthcare workers

Objectives
Exposure to infection is an inherent occupational risk for healthcare workers and may lead them to undergo quarantine during disease outbreaks. Both front-line battle and quarantine are stressful experiences that may make psychological support for healthcare workers necessary. Psychological support measures based on the best available evidence should be included in emergency plans worldwide. We summarise the research evidence on the psychological impact of quarantine on healthcare workers.

Methods
We retrieved 470 articles on the psychological impact of quarantine on healthcare workers from the Web of Science and included in this review all 12 articles that met our inclusion criteria.

Results
The reviewed studies reported acute stress during quarantine and long-lasting depressive, post-traumatic stress and alcohol dependency and abuse symptoms. Healthcare workers fear infection for themselves, but more so for their loved ones, and are also concerned about the stigma that may affect their families, most especially their children.

Conclusions
The safety of healthcare workers and their families during disease outbreaks needs to be ensured. Suitable alternative accommodation and personalised monitoring during quarantine are useful intervention measures to prevent adverse effects in healthcare workers. Clear public health communication will help reduce uncertainty, guilt and stigma. Financial aid should be considered for the more severely affected workers. Finally, mental healthcare for healthcare workers should be a priority, as quarantines can be a mental distress trigger. The development of efficient referral paths and the provision of counselling or psychotherapy during the confinement period are an opportunity for early mental health interventions.

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http://oem.bmj.com/cgi/content/short/77/10/666?rss=1

Suicide deaths among diagnostic medical radiation workers in South Korea, 1996-2017

Objectives
Suicide is a leading cause of death in the working-age population. We investigated suicide mortality among diagnostic medical radiation workers in relation to their demographic and occupational factors in South Korea.

Methods
The study population consisted of all diagnostic medical radiation workers enrolled in the National Dosimetry Registry from 1996 to 2011. The registry data were linked with mortality data through the end of 2017. We calculated age-standardised suicide rates, standardised mortality ratios (SMRs) and rate ratios (RRs) by demographic and occupational factors.

Results
A total of 207 suicides were identified among 94 367 medical radiation workers, exhibiting a suicide rate of 14.0 per 100 000 person-years. Compared with the general population, suicide rates were lower for both male and female workers (SMR 0.49, 95% confidence interval (CI) 0.42 to 0.57; SMR 0.54, 95% CI 0.41 to 0.70, respectively). Similarly, decreased SMRs were observed across job titles and other work-related factors. However, a shorter duration of employment was positively associated with RRs for suicide; risks were 2.74 (95% CI 1.56 to 4.81) and 4.66 (95% CI 1.53 to 14.20) times higher in male and female workers with less than 1 year of employment, respectively, than in those with at least 10 years of employment.

Conclusions
Diagnostic medical radiation workers in South Korea showed lower suicide rates than in the general population. However, a shorter duration of employment was associated with higher risk of suicide. Suicide prevention efforts could target workers engaged in short-term employment.

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http://oem.bmj.com/cgi/content/short/77/10/675?rss=1

Prospective study of job stress and risk of infections in Swedish adults

Objectives
Psychological stress may influence both susceptibility and severity of infections. Although work-related stress is a widespread concern among many employees, few studies have been conducted with the focus on work stressors and infections. We therefore aimed to investigate this association in a prospective cohort study.

Methods
Our study included 25 029 employed individuals who filled-out a questionnaire in September 1997 and were followed through record linkages until retirement or December 2016. Work stress was assessed at baseline using a Swedish version of the Demand-Control Questionnaire, whereas hospital contacts related to infections were identified from the National Patient Register. We fitted extensions of the standard Cox model to account for recurrent infections.

Results
In total, we observed 8257 infections. Individuals in the third tertile of job demand had a 13% higher hazard of infections (HR=1.13; 95% CI=1.03 to 1.24) compared with individuals in the first tertile, specifically an increased incidence of upper respiratory tract infections (HR=1.15; 95% CI=1.00 to 1.33) and urinary tract infections (HR=1.31; 95% CI=1.09 to 1.57) was found. Employees with the highest job control (third tertile) had no lower risk of infections than individuals in the lowest tertile (HR=1.02; 95% CI=0.92 to 1.13). When combining the demand and control dimensions into job strain scale, no association between high job strain and infections was observed (HR=1.08; 95% CI=0.97 to 1.21).

Conclusion
High job demand, but not low job control, is associated with an increased occurrence of infections. No difference was observed in workers with high strain jobs compared with those with low strain jobs.

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http://oem.bmj.com/cgi/content/short/77/10/681?rss=1

Occupational exposure to whole-body vibrations and pregnancy complications: a nationwide cohort study in Sweden

Objectives
Pregnancy complications are common contributors to perinatal mortality and morbidity. Still, the cause(s) of gestational hypertensive disorders and diabetes are largely unknown. Some occupational exposures have been inconsistently associated with pregnancy complications, but exposure to whole-body vibrations (WBV) has been largely overlooked even though it has been associated with adverse birth outcomes. Therefore, the aim was to assess whether occupational WBV exposure during pregnancy is associated with pregnancy complications in a nationwide, prospective cohort study.

Methods
The Fetal Air Pollution Exposure cohort was formed by merging multiple Swedish, national registers containing information on occupation during pregnancy and diagnosis codes, and includes all working women who gave birth between 1994 and 2014 (n=1 091 044). WBV exposure was derived from a job-exposure matrix and was divided into categories (0, 0.1–0.2, 0.3–0.4 and ≥0.5 m/s2). ORs with 95% CIs were calculated using logistic regression adjusted for potential confounders.

Results
Among women working full time (n=646 490), we found increased risks of all pregnancy complications in the highest exposure group (≥0.5 m/s2), compared with the lowest. The adjusted ORs were 1.76 (95% CI 1.41 to 2.20), 1.55 (95% CI 1.26 to 1.91) and 1.62 (95% CI 1.07 to 2.46) for preeclampsia, gestational hypertension and gestational diabetes, respectively, and were similar in all sensitivity analyses. There were no clear associations for part-time workers.

Conclusions
The results suggest that women should not be exposed to WBV at/above the action limit value of 0.5 m/s2 (European directive) continuously through pregnancy. However, these results need further confirmation.

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http://oem.bmj.com/cgi/content/short/77/10/691?rss=1

Long work hours and decreased glomerular filtration rate in the Korean working population

Objectives
We studied the association between long working hours and decreased kidney function, which was determined using estimated glomerular filtration rate (eGFR), among the working population in South Korea.

Methods
We analysed nationally representative cross-sectional data for 20 851 Korean workers ≥20 years of age. A negative binomial regression model was used to test differences in the prevalence of chronic kidney disease (eGFR <60 mL/min/1.73 m2) among workers divided into groups according to weekly working hours (<30, 30–40, 41–51 and ≥52 hours/week). Multivariate linear regression analysis was performed to investigate the association between weekly working hours and eGFR, with adjustments made for age, sex/gender, income, education, shift work, occupation, smoking, alcohol use, hypertension, diabetes mellitus, body mass index, systolic blood pressure, fasting blood glucose and total serum cholesterol.

Results
A 1-hour increase in weekly working hours was associated with 0.057 mL/min/1.73 m2 (95% CI 0.005 to 0.109) decrease in eGFR among participants who worked ≥52 hours/week. Among participants without hypertension or diabetes, a 1-hour increase in weekly working hours was significantly associated with 0.248 and 0.209 mL/min/1.73 m2 decrease in eGFR among participants who worked 30–40 hours/week and 41–51 hours/week, respectively.

Conclusion
Long working hours are associated with decreased kidney function. We expect that our findings could call for more research regarding this association and provide policy-oriented perspectives.

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http://oem.bmj.com/cgi/content/short/77/10/699?rss=1

Exposure-response assessment of cancer mortality in styrene-exposed boatbuilders

Objectives
To improve exposure estimates and reexamine exposure–response relationships between cumulative styrene exposure and cancer mortality in a previously studied cohort of US boatbuilders exposed between 1959 and 1978 and followed through 2016.

Methods
Cumulative styrene exposure was estimated from work assignments and air-sampling data. Exposure–response relationships between styrene and select cancers were examined in Cox proportional hazards models matched on attained age, sex, race, birth cohort and employment duration. Models adjusted for socioeconomic status (SES). Exposures were lagged 10 years or by a period maximising the likelihood. HRs included 95% profile-likelihood CIs. Actuarial methods were used to estimate the styrene exposure corresponding to 10-4 extra lifetime risk.

Results
The cohort (n= 5163) contributed 201 951 person-years. Exposures were right-skewed, with mean and median of 31 and 5.7 ppm-years, respectively. Positive, monotonic exposure–response associations were evident for leukaemia (HR at 50 ppm-years styrene = 1.46; 95% CI 1.04 to 1.97) and bladder cancer (HR at 50 ppm-years styrene =1.64; 95% CI 1.14 to 2.33). There was no evidence of confounding by SES. A working lifetime exposure to 0.05 ppm styrene corresponded to one extra leukaemia death per 10 000 workers.

Conclusions
The study contributes evidence of exposure–response associations between cumulative styrene exposure and cancer. Simple risk projections at current exposure levels indicate a need for formal risk assessment. Future recommendations on worker protection would benefit from additional research clarifying cancer risks from styrene exposure.

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http://oem.bmj.com/cgi/content/short/77/10/706?rss=1

Exposure to cholinesterase inhibiting insecticides and blood glucose level in a population of Ugandan smallholder farmers

Objectives
The risk of diabetes mellitus may be elevated among persons exposed to some pesticides, including cholinesterase-inhibiting insecticides (organophosphates and carbamates). The objective of this study was to investigate how acetylcholinesterase activity was associated with mean blood glucose levels among smallholder farmers in Uganda.

Methods
We conducted a short-term follow-up study among 364 smallholder farmers in Uganda. Participants were examined three times from September 2018 to February 2019. At each visit, we measured glycosylated haemoglobin A (HbA1c) as a measure of long-term average blood glucose levels. Exposure to organophosphate and carbamate insecticides was quantified using erythrocyte acetylcholinesterase normalised by haemoglobin (AChE/Hb). For a subgroup of participants, fasting plasma glucose (FPG) was also available. We analysed HbA1c and FPG versus AChE/Hb in linear mixed and fixed effect models adjusting for age, sex, physical activity level, and consumption of fruits and vegetables, alcohol and tobacco.

Results
Contrary to our hypothesis, our mixed effect models showed significant correlation between low AChE/Hb and low HbA1c. Adjusted mean HbA1c was 0.74 (95% CI 0.17 to 1.31) mmol/mol lower for subjects with AChE/Hb=24.3 U/g (35th percentile) compared with subjects with AChE/Hb=25.8 U/g (50th percentile). Similar results were demonstrated for FPG. Fixed effect models showed less clear correlations for between-phase changes in AChE/Hb and HbA1c.

Conclusions
Our results do not clearly support a causal link between exposure to cholinesterase-inhibiting insecticides and elevated blood glucose levels (expressed as HbA1c and FPG), but results should be interpreted with caution due to the risk of reverse causality.

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http://oem.bmj.com/cgi/content/short/77/10/713?rss=1

Maternal preconception and first trimester exposure to PM10 and the risk of oral clefts in offspring: a population-based, case-control study

Background
Current literature describes limited and controversial evidence on the associations between maternal preconception and first trimester exposure to particulate matter with a diameter ≤10 µm (PM10) and the risk of oral cleft (OC).

Methods
We conducted a case–control study involving 3086 OC cases and 7950 controls, registered in the Maternal and Child Health Certificate Registry in Liaoning Province between 2010 and 2015. PM10 concentrations were obtained from the Environment Protection Bureau. The exposure windows included the 3 months before pregnancy, the first trimester and the individual months. Unconditional logistic regression model was performed to estimate the OR and 95% CI for the association between PM10 exposure and the risk of OC, cleft lip only (CLO), cleft palate only (CPO), and cleft lip and palate (CLP).

Results
Maternal PM10 exposure was positively associated with an increased risk for OC during the 3 months preconception (per 10 µg/m3 increment: OR=1.04, 95% CI 1.01 to 1.07; highest vs lowest quartile: OR=1.23, 95% CI 1.04 to 1.45) and the first trimester (per 10 µg/m3 increment: OR=1.05, 95% CI 1.02 to 1.08; highest vs lowest quartile: OR=1.37, 95% CI 1.15 to 1.64). Analyses based on individual months presented similar positive associations, particularly in the second month of pregnancy (OR=1.77, 95% CI 1.51 to 2.09) for highest versus lowest quartile. In the subtype analysis, stronger associations were observed for CLO, whereas there was negligible evidence for CPO and CLP. Sensitivity analyses using propensity score matching generated similar findings.

Conclusions
Our study provides evidence that PM10 exposure during the 3 months preconception and the first trimester increases the risk of OC.

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http://oem.bmj.com/cgi/content/short/77/10/721?rss=1

Identification of late asthmatic reactions following specific inhalation challenge

Specific inhalation challenge (SIC) is the reference standard for the diagnosis of occupational asthma. Current guidelines for identifying late asthmatic reactions are not evidence based.
Objectives
To identify the fall in forced expiratory volume in 1 s (FEV1) required following SIC to exceed the 95% CI for control days, factors which influence this and to show how this can be applied in routine practice using a statistical method based on the pooled SD for FEV1 from three control days.

Methods
Fifty consecutive workers being investigated for occupational asthma were asked to self-record FEV1 hourly for 2 days before admission for SIC. These 2 days were added to the in-hospital control day to calculate the pooled SD and 95% CI.

Results
45/50 kept adequate measurements. The pooled 95% CI was 385 mL (SD 126), or 14.2% (SD 6.2) of the baseline FEV1, but was unrelated to the baseline FEV1 (r=0.06, p=0.68), or gender, atopy, smoking, non-specific reactivity or treatment before or during SIC. Thirteen workers had a late asthmatic reaction with ≥2 consecutive FEV1 measurements below the 95% CI for pooled control days, 4/13 had <15% and 9/13 >15% late fall from baseline. The four workers with ≥2 values below the 95% CI all had independent evidence of occupational asthma.

Conclusion
The pooled SD method for defining late asthmatic reactions has scientific validity, accounts for interpatient spirometric variability and diurnal variation and can identify clinically relevant late asthmatic reactions from smaller exposures. For baseline FEV1 <2.5 L, a 15% fall is within the 95% CI.

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http://oem.bmj.com/cgi/content/short/77/10/728?rss=1

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