The asbestos-asbestosis exposure-response relationship: a cohort study of the general working population.

OBJECTIVES: The association between asbestos exposure and asbestosis in high-exposed industrial cohorts is well-known, but there is a lack of knowledge about the exposure-response relationship for asbestosis in a general working population setting. We examined the exposure-response relationship between occupational asbestos exposure and asbestosis in asbestos-exposed workers of the Danish general working population. METHODS: We followed all asbestos-exposed workers from 1979 to 2015 and identified incident cases of asbestosis using the Danish National Patient Register. Individual asbestos exposure was estimated with a quantitative job exposure matrix (SYN-JEM) from 1976 onwards and back-extrapolated to age 16 for those exposed in 1976. Exposure-response relations for cumulative exposure and other exposure metrics were analyzed using a discrete time hazard model and adjusted for potential confounders. RESULTS: The range of cumulative exposure in the population was 0.001 to 18 fibers per milliliter-year (f/ml-year). We found increasing incidence rate ratios (IRR) of asbestosis with increasing cumulative asbestos exposure with a fully adjusted IRR per 1 f/ml-years of 1.18 [95% confidence interval (CI) 1.15- -1.22]. The IRR was 1.94 (95% CI 1.53-2.47) in the highest compared to the lowest exposure tertile. We similarly observed increasing risk with increasing cumulative exposure in the inception population. CONCLUSIONS: This study found exposure-response relations between cumulative asbestos exposure and incident asbestosis in the Danish general working population with mainly low-level exposed occupations, but there is some uncertainty regarding the exposure levels.

Validity of self-reported night shift work among women with and without breast cancer.

OBJECTIVES: This study aimed to estimate the validity of self-reported information on ever-night shift work among women with and without breast cancer and illustrate the consequences for breast cancer risk estimates. METHODS: During 2015-2016, 225 women diagnosed with breast cancer and 1800 matched controls without breast cancer employed within the Danish hospital regions during 2007-2016 participated in a questionnaire-based survey. Their reported night shift work status was linked with objective payroll register day-by-day working hour data from the Danish Working Hour Database and the Danish Cancer Registry. For the breast cancer patients and their matched controls, we estimated sensitivity and specificity for ever-working night shifts using the payroll data as the gold standard. We also used quantitative bias analysis to estimate the impact on relative risk estimates for a hypothetical population. RESULTS: For breast cancer patients, we observed a sensitivity of ever-night shifts of 86.2% and a specificity of never-night shifts of 82.6%. For controls, the sensitivity was 80.6% and the specificity 83.7%. Odds ratio for breast cancer in a hypothetical population decreased from 1.12 [95% confidence interval (CI) 1.03-1.21] to 1.05 (95% CI 0.95-1.16) when corrected by the sensitivity and specificity estimates. CONCLUSION: This study shows that female breast cancer patients had slightly better recall of previous night shift work than controls. Additionally, both breast cancer patients and controls recalled previous never-night shift work with low specificity. The net effect of this misclassification is a small over-estimation of the relative breast cancer risk due to night shift work.

Long-term follow-up study of work status among patients with work-related mental disorders referred to departments of occupational medicine in Denmark.

OBJECTIVES: To describe the 5 year work status in patients referred for suspected work-related common mental disorders. To develop a prognostic model. DESIGN: Register-based nationwide longitudinal follow-up study. SETTING: All departments of occupational medicine in Denmark. PARTICIPANTS: 17 822 patients aged 18-67 years, seen for the first time at a Department of Occupational Medicine in Denmark from 2000 to 2013 and diagnosed with stress, depression, post-traumatic stress disorder, anxiety or other mental disorders. INTERVENTIONS: All patients were seen for diagnostic assessment and causal evaluation of the work-relatedness of their disorders. Some departments offered patients with stress disorders psychological treatment, which, however, was not organised according to patient selection or type of treatment. PRIMARY AND SECONDARY OUTCOME MEASURES: Register data were collected for 5 year periods before and after the patients' first assessment at a department. Weekly percentages of patients are presented according to work status. The outcome in the prognostic model was a high Work Participation Score (ie, working>75% of potential work weeks/year) at 5 year follow-up. RESULTS: For all subgroups of patients, a high proportion were working (>75%) 1-5 years before assessment, and all experienced a large reduction in work status at time of assessment. At 1 year follow-up, almost 60% of patients with stress were working, whereas in the other patient subgroups, less than 40% were working. In the following years, practically no increase was observed in the percentage of patients working in any of the subgroups. Based on these 5 year follow-up data, we developed a work participation model with only moderate discrimination and calibration. CONCLUSIONS: In Denmark, not all return to previous work status 5 years after a referral due to a suspected work-related common mental disorder. We developed a prognostic model with only moderate discrimination and calibration for long-term work participation after suggested work-related common mental disorders.

Night shift work characteristics and risk of incident coronary heart disease among health care workers: national cohort study.

BACKGROUND: Night work has been associated with coronary heart disease. The present study examined exposure-response relations between quantitative night work characteristics and coronary heart disease (angina pectoris or myocardial infarction) with the aim to contribute to evidence-based recommendations for low-risk night work schedules. METHODS: We followed 100 149 night workers (80% women) and 153 882 day workers (78% women), all health care workers in Denmark with day by day payroll information on night shifts from 2007 to 2015. We analysed data with Poisson regression stratified by sex and adjusted for age, calendar year, diabetes, family history of cardiovascular disease, educational level, occupation, indicators for obesity, hypercholesterolaemia, and hypertension. RESULTS: Female and male night workers worked on average 1.7 and 1.8 night shifts per month for an average duration of less than 4 years. During follow-up, 1198 night and 2128 day workers were hospitalized with first-time coronary heart disease. When compared with day workers, the overall incidence rate ratios for female and male night workers were 1.06 [95% confidence interval (CI): 0.97, 1.17] and 1.22 (95% CI 1.07, 1.39). Highest risks were observed in top exposure categories for several night work characteristics. However, no consistent exposure-response relations by number of monthly night shifts, cumulative night shifts, years with rotating night shifts, years with any night shift and consecutive night shifts were observed among the night workers of either sex. CONCLUSIONS: This study of a population with low exposure to night work does not indicate that reducing extent of monthly night shifts, cumulative night shifts, years with rotating night shifts, years with any night shift and consecutive night shifts would reduce the risk of coronary heart disease.

Developing prognostic models for health care utilization in patients with work-related mental health problems.

BACKGROUND: The long-term prognosis for employees with work-related mental health problems is unclear. We aim to describe long-term trends in health care utilization (HCU) and develop multivariable prognostic models for long-term mental health care utilization. METHODS: From the Danish Occupational Medicine Cohort we included mental health patients (N = 17,822) assessed from 2000 to 2013 at Departments of Occupational Medicine. Outcomes were general health (general practitioner, somatic hospital) and mental health (psychiatrist/psychologist, psychiatric hospital) HCU obtained from registries five years before/after assessment. The 10-year period was divided into phases relative to assessment: 5 - 3 years before, 2 years before/after, and 3-5 years after. We developed gender-stratified Lasso-penalized multivariable prognostic models for HCU 3-5 years after assessment assessing both calibration and discrimination. RESULTS: Prevalent HCU for general practitioner, psychiatrist/psychologist and psychiatric hospital services was relatively stable 5 - 3 years prior to assessment, then rising during the 2 years before/after. At 3-5 years after assessment prevalent general practitioner HCU declined to previous levels, while prevalent HCU for psychologist/psychiatrist and psychiatric hospital services remained elevated compared to previous levels during years 5 - 3. Prognostic models for long-term psychologist/psychiatrist and psychiatric hospital HCU indicated acceptable calibration and modest discrimination. CONCLUSIONS: Prevalent HCU rose two years before/after assessment and remained elevated for psychiatrist/psychologist and psychiatric hospital HCU 3-5 years after. Gender-stratified prognostic models were developed for long-term mental health HCU, but discrimination and calibration should be further improved before out-of-sample application for personal prognosis. TRIAL REGISTRATION: The study was registered at clinicaltrials.gov (Identifier: NCT04459793) prior to analyses.

SARS-CoV-2 Infection Rates Following Use of Regular Compared With Defective Respirators When Caring for COVID-19 Patients: A Retrospective Follow-up Study.

BACKGROUND: There is strong observational evidence that respirators are highly effective in protecting the users from being infected with Middle East respiratory syndrome and severe acute respiratory syndrome coronavirus (SARS-CoV), but the evidence for SARS-CoV-2 during daily work is limited. This study utilized a subset of healthcare workers' temporary use of a new brand respirator with frequent defects when caring for coronavirus disease 2019 (COVID-19) patients to assess the protective effect of regular respirators against SARS-CoV-2 infection. METHODS: We retrospectively followed 463 participants wearing a regular respirator and 168 wearing the new brand respirator day-by-day when caring for COVID-19 patients until testing polymerase chain reaction positive for SARS-CoV-2 between 27th December 2020 and 14th January 2021. RESULTS: We observed seven and eight incident SARS-CoV-2-infected cases. This corresponded with daily infection rates of 0.2 and 0.5%, an incidence rate ratio of 0.4 [95% confidence interval (CI) 0.1; 1.0], and an incidence rate difference of 0.3% (95% CI -0.1; 0.8) when comparing a regular with the new brand respirator. DISCUSSION: We regard the new brand respirator a sham intervention, and this study thus provides further evidence for the protective effect of respirators when exposed to SARS-CoV-2 virus.

Use of Personal Protective Equipment Among Healthcare Workers During the First and the Second Wave of the COVID-19 Pandemic.

INTRODUCTION: To treat and properly care for COVID-19 patients it is vital to have healthy healthcare workers to ensure the continued function of the healthcare system and to prevent transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to patients, co-workers, and the community. Personal protective equipment (PPE) can prevent healthcare workers from being infected with and transmitting SARS-CoV-2. Experience and training are pivotal to ensure optimal protection. This study aims to examine the use and failure of PPE and compliance with PPE guidelines during the first and the second wave of the COVID-19 pandemic among Danish healthcare workers. METHODS: Healthcare workers from the Central Denmark Region and the Capital Region of Denmark were invited to participate April-June 2020 during the first wave and November 2020-April 2021 during the second wave. Day-by-day, participants reported work procedures, use and failure of PPE, and compliance with PPE guidelines. Register-based information on sex, age, department, and profession was available for all participants. RESULTS: In total, 21 684 and 10 097 healthcare workers participated during the first and the second wave, respectively. During the first wave, 1.7% used filtering face piece-2 or -3 (FFP2 or FFP3) respirators and 8.2% used face masks [fluid resistant (type IIR) masks, masks with visor (typically type IIR), and other unspecified face masks] during physical contact with patients. During the second wave, the corresponding figures increased to 17.8% and 80.7%. During respiratory procedures, the use of FFP2 or FFP3 respirators increased from 5.6 to 24.3%, and the use of face masks from 14.7 to 77.8%. The no PPE use decreased from 21.3% during the first wave to 0.4% in the second wave, during respiratory procedures. Total PPE failures decreased from 0.7 to 0.4% from the first to second wave. The proportion not complying with PPE guidelines declined from 3.6 to 2.2% during physical contact with patients and from 6.5 to 4.6% during respiratory procedures. PPE failure and non-compliance varied by age, sex and type of department. Frequent reasons for non-compliance were forgetfulness and lack of time, and during the first but not during the second wave, limited availability of PPE. CONCLUSION: We found a substantial increase in the use of PPE and a substantial decrease in PPE failures from the first to the second wave of COVID-19 in Denmark. However, there is still a need for continuous focus on compliance in use of PPE among healthcare workers.

Risk of myocardial infarction among pigeon breeders: A follow-up study.

Pigeon breeders are exposed to high levels of fine particulate organic matter in the pigeon lofts. A total of 6,704 pigeon breeders and their 1:30 sex and age-matched referents from the general Danish population were followed from 1980 or first year of membership in the Danish Racing Pigeon Association, until first event of myocardial infarction, emigration, death, or end of study, on December 31, 2013. Information on outcomes and covariates was obtained by record linkage with national registers. Stratified Cox regression models estimated the hazard ratio of myocardial infarction, adjusted for occupation and residence at the start of follow-up. Compared with referents, pigeon breeders had an adjusted hazard ratio of 1.14 (95% CI: 1.05-1.22) for myocardial infarction. Exposure to pigeon-derived organic dust may increase the risk of myocardial infarction, but this finding needs to be corroborated.

Healthcare workers' SARS-CoV-2 infection rates during the second wave of the pandemic: follow-up study.

OBJECTIVES: This study aimed to assess if, during the second wave of the COVID-19 pandemic, healthcare workers had increased severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection rates, following close contact with patients, co-workers and persons outside work with COVID-19. METHODS: A follow-up study of 5985 healthcare workers from Denmark was conducted between November 2020 and April 2021 and provided day-to-day information on COVID-19 contacts. SARS-CoV-2 infection was defined by the first positive polymerase chain reaction (PCR) test ever. Data was analyzed in multivariable Poisson regression models. RESULTS: The SARS-CoV-2 infection rates following close contact 3-7 days earlier with patients, co-workers and persons outside work with COVID-19 were 153.7, 240.8, and 728.1 per 100 000 person-days, respectively. This corresponded with age, sex, month, number of PCR tests and mutually adjusted incidence rate ratios of 3.17 [40 cases, 95% confidence interval (CI) 2.15-4.66], 2.54 (10 cases, 95% CI 1.30-4.96) and 17.79 (35 cases, 95% CI 12.05-26.28). The risk of SARS-CoV-2 infection was thus lower, but the absolute numbers affected was higher following COVID-19 contact at work than COVID-19 contact off work. CONCLUSIONS: Despite strong focus on preventive measures during the second wave of the pandemic, healthcare workers were still at increased risk of SARS-CoV-2 infection when in close contact with patients or co-workers with COVID-19. There is a need for increased focus on infection control measures in order to secure healthcare workers' health and reduce transmission into the community during ongoing and future waves of SARS-CoV-2 and other infections.

Neurological symptoms and disorders following electrical injury: A register-based matched cohort study.

INTRODUCTION: Electric shocks may have neurological consequences for the victims. Although the literature on the neurological consequences of electric shocks is limited by retrospective designs, case studies and studies of selected patient groups, previous research provides some evidence of a link between electric shocks, and diseases and symptoms of the central nervous system (CNS)(e.g. epilepsy, migraine and vertigo) and the peripheral nervous system (PNS)(e.g. loss of sensation, neuropathy and muscle weakness). This study aims to employ a register-based, matched cohort study, to investigate whether individuals demonstrate a greater risk of neurological diseases and symptoms of the CNS or PNS in the years following an electrical injury. MATERIALS AND METHODS: We identified 14,112 electrical injuries over a period of 19 years in two Danish registries, and matched these with three different groups of persons in a prospective matched cohort study: (1) patients with dislocation/sprain injuries, (2) patients with eye injuries and (3) persons employed in the same occupation. Year of injury, sex and age were used as matching variables. The outcomes we identified comprised neurological disorders and central or peripheral nervous system symptoms that covered a range of diagnoses in the Danish National Patient Register. The associations were analysed using conditional logistic regression for a range of time periods (six months to five years) and conditional Cox regression for analyses of the complete follow-up period (up to 20 years). RESULTS: For victims of electric shock, the CNS sequelae we identified included an increased risk of epilepsy, convulsions, abnormal involuntary movements, headache, migraine and vertigo. We also identified an uncertain, increased risk of spinal muscular atrophy and dystonia, whereas we identified no increased risk of Parkinson's disease, essential tremor, multiple sclerosis or other degenerative diseases of the nervous system. For victims of electric shock, the PNS sequelae we identified included an increased risk of disturbances of skin sensation, mononeuropathy in the arm or leg and nerve root and plexus disorders. We also identified an uncertain, increased risk of facial nerve disorders, other mononeuropathy, and polyneuropathy. CONCLUSION: Our results confirm that electrical injuries increase the risk of several neurological diseases and symptoms of the CNS or PNS in the years following the injury. Most often the diseases and symptoms are diagnosed within the first six months of the injury, but delayed onset of up to 5 years cannot be ruled out for some symptoms and diagnoses. Some of the conditions were rare in our population, which limited our ability to identify associations, and this warrants cautious interpretation. Therefore, further studies are needed to confirm our findings, as are studies that examine the mechanisms underlying these associations.

A longitudinal study of morning, evening, and night light intensities and nocturnal sleep quality in a working population.

We aimed to investigate whether higher light intensity in the morning is associated with better nocturnal sleep quality and whether higher light intensities in the evening or night have the opposite effect. Light intensity was recorded for 7 consecutive days across the year among 317 indoor and outdoor daytime workers in Denmark (55-56° N) equipped with a personal light recorder. Participants reported sleep quality after each nocturnal sleep. Sleep quality was measured using three parameters; disturbed sleep index, awakening index, and sleep onset latency. Associations between increasing light intensities and sleep quality were analyzed using mixed effects models with participant identity as a random effect. Overall, neither white nor blue light intensities during morning, evening, or night were associated with sleep quality, awakening, or sleep onset latency of the subsequent nocturnal sleep. However, secondary analyses suggested that artificial light during the morning and day contrary to solar light may increase vulnerability to evening light exposure. Altogether, we were not able to confirm that higher morning light intensity significantly improves self-reported sleep quality or that higher evening or night light intensities impair self-reported sleep quality at exposure levels encountered during daily life in a working population in Denmark. This suggests that light intensities alone are not important for sleep quality to a degree that it is distinguishable from other important parameters in daily life settings.

Unspecified pain and other soft tissue disorders following electrical injuries: a register-based matched cohort study.

OBJECTIVE: This study investigates whether individuals who have sustained an electrical injury (EI) are diagnosed with unspecified pain or pain related to the musculoskeletal system in the years following the injury. METHODS: Individuals listed in Danish registers as having sustained EIs were matched for sex, age, and year of injury in a cohort study with individuals having experienced dislocations/sprains (match 1), eye injuries (match 2), and a sample of individuals with the same occupation without a history of electrical injuries (match 3). Outcomes were unspecified pain and unspecified soft tissue disorders. Conditional logistic regression and conditional Cox regression were applied. RESULTS: We identified 14,112 individuals who sustained EIs. A higher risk of both outcomes was observed for all three matches, and was highest at the 6- and 12-month follow-ups. The risk of both outcomes was considerably higher for match 3. CONCLUSIONS: This study confirms that exposure to EIs increases the risk of being diagnosed with unspecified pain or unspecified soft tissue disorders both at short and long terms. Our results also showed that the risk of unspecified pain as sequelae is related to the severity of the injury.

Serum levels of IgG antibodies against Aspergillus fumigatus and the risk of hypersensitivity pneumonitis and other interstitial lung diseases.

Hypersensitivity pneumonitis (HP) is an interstitial lung disease (ILD) caused by the inhalation of antigens. Antigen-specific IgG antibodies (sIgG) are used as biomarkers of exposure when diagnosing HP, but little is known about the longitudinal relation between antibody levels and risk of HP or other ILD. In a follow-up design, we explored the relationship between sIgG antibodies against Aspergillus fumigatus and the diagnosis of HP in 647 subjects suspected of HP. We showed that IgG levels above the reference value resulted in a hazard ratio of 9.5 for subsequent HP. Our findings support a relationship between high levels of sIgG against A. fumigatus and risk of HP.

Symptoms reported by SARS-CoV-2 seropositive and seronegative healthcare and administrative employees in Denmark from May to August 2020.

BACKGROUND: The distribution and nature of symptoms among SARS-CoV-2 infected individuals need to be clarified. METHODS: Between May and August 2020, 11 138 healthcare and administrative personnel from Central Denmark Region were tested for SARS-CoV-2 antibodies and subsequently completed a questionnaire. Symptom prevalence and overall duration for symptoms persisting for more than 30 days were calculated. Logistic regression models were used to estimate adjusted odds ratios (ORs) with 95% CIs. RESULTS: In total, 447 (4%) of the participants were SARS-CoV-2-seropositive. Loss of sense of smell and taste was reported by 50% of seropositives compared with 3% of seronegatives. Additionally, seropositives more frequently reported fever, dyspnoea, muscle or joint ache, fatigue, cough, headache and sore throat, and they were more likely to report symptoms persisting for more than 30 days. In adjusted models, they had a higher risk of reporting symptoms, with the strongest association observed for loss of sense of taste and smell (OR = 35.6; 95% CI: 28.6-44.3). CONCLUSION: In this large study, SARS-CoV-2-seropositive participants reported COVID-19-associated symptoms more frequently than those who were seronegative, especially loss of sense of taste and smell. Overall, their symptoms were also more likely to persist for more than 30 days.

Day-by-day symptoms following positive and negative PCR tests for SARS-CoV-2 in non-hospitalized healthcare workers: A 90-day follow-up study.

OBJECTIVE: Our study aimed to compare symptoms day by day for non-hospitalized individuals testing positive and negative for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). METHODS: In total, 210 positive-test and 630 negative-test healthcare workers in the Central Denmark Region were followed for up to 90 days after testing, between April and June, 2020. Their daily reported COVID-19-related symptoms were compared graphically and by logistic regression. RESULTS: Thirty per cent of the positive-test and close to 0% of the negative-test participants reported a reduced sense of taste and smell during all 90 days (adjusted odds ratio [aOR] 86.07, 95% CI 22.86-323). Dyspnea was reported by an initial 20% of positive-test participants, declining to 5% after 30 days, without ever reaching the level of the negative-test participants (aOR 6.88, 95% CI 2.41-19.63). Cough, headache, sore throat, muscle pain, and fever were temporarily more prevalent among the positive-test participants; after 30 days, no increases were seen. Women and older participants were more susceptible to long-lasting COVID-19 symptoms. CONCLUSION: The prevalence of long-lasting reduced sense of taste and smell is highly increased in mild COVID-19 patients. This pattern is also seen for dyspnea at a low level, but not for cough, sore throat, headache, muscle pain, or fever.

How does engagement in society in adolescence affect educational attainment and employment in early adulthood: A prospective cohort study.

INTRODUCTION: Educational attainment and employment are essential for young people to develop the skills needed to participate in society and maintain a stable connection to the labour market in adult life. The objective of this study was to examine associations between engagement in society, measured by leisure time activities and part-time work in mid and late adolescence and educational attainment and employment in early adulthood. METHOD: A cohort of Danish young people born in 1989 was followed in a prospective study with questionnaires in 2004 (n = 3,054) and 2007 (n = 2,400) where information on leisure time activities and part-time work was collected. Information on connection to education and work was collected from a register of social benefits when participants were 25-29 years old and divided into high and low connection. The associations were examined using logistic regression and stratified by gender and childhood socioeconomic groups. RESULTS: Part-time work was, both in mid (OR: 1.7 [95% CI 1.3; 2.2]) and late (1.9 [1.4;2.6]) adolescence, positively associated with connection to education and work. Leisure time activities in mid adolescence were associated with connection to education and work (OR:1.6 [1.2;2.1]). Among men engagement in society showed strongest associations with later connection to education or work in mid adolescence (ORs up to 2.2), whereas the associations for women seemed strongest in late adolescence (ORs up to 2.8). CONCLUSION: The study showed that adolescent engagement in society had positive associations with later educational attainment and employment, with stronger impact of part-time work compared to leisure time activities. The study identified differences between genders and the timing of engagement. Associations were consistent across socioeconomic groups.

Mental disorders following electrical injuries-A register-based, matched cohort study.

INTRODUCTION: Electrical injuries happen every day in homes and workplaces. Not only may these injuries cause physical damage and disability, they may also cause mental disorders. The aim of this study was to investigate if persons with an electrical injury suffer from mental disorders in the following years. MATERIAL AND METHODS: In a prospective matched cohort design, we identified 14.112 electrical injuries in two Danish registries and matched these with persons with dislocation/sprain injuries or eye injuries, respectively, as well as with persons from the workforce from the same occupation, using year of injury, sex and age as matching variables. We identified possible outcomes in terms of mental diagnoses in the Danish National Patient registry, based on literature, including reviews, original studies and case-reports as well as experiences from clinical praxis. The associations were analyzed using conditional cox- and logistic regression. RESULTS: We found that the following of the examined outcomes were associated with exposure to an electrical injury compared to the matched controls. Some of the outcomes showed the strongest associations shortly after the injury, namely 'mental disorders due to known physiological condition', 'anxiety and adjustment disorders', and especially the 'Post Traumatic Stress Disorder (PTSD)' subgroup. The same pattern was seen for 'Depression' although the associations were weaker. Other conditions took time to develop ('Somatoform disorders'), or were only present in the time to event analysis ('other non-psychotic mental disorders' and 'sleep disorders'). The findings were consistent in all three matches, with the highest risk estimates in the occupation match. CONCLUSION: Electrical injuries may result in mental disorders, both acute and several years after. However, the absolute risk is limited as most of the outcomes are rare.

Occupational exposure to respirable crystalline silica and risk of autoimmune rheumatic diseases: a nationwide cohort study.

BACKGROUND: Exposure to respirable crystalline silica is suggested to increase the risk of autoimmune rheumatic diseases. We examined the association between respirable crystalline silica exposure and systemic sclerosis, rheumatoid arthritis, systemic lupus erythematosus and small vessel vasculitis. METHODS: In a cohort study of the total Danish working population, we included 1 541 505 male and 1 470 769 female workers followed since entering the labour market 1979-2015. Each worker was annually assigned a level of respirable crystalline silica exposure estimated with a quantitative job exposure matrix. We identified cases of autoimmune rheumatic diseases in a national patient register and examined sex-specific exposure-response relations by cumulative exposure and other exposure metrics. RESULTS: We identified 4673 male and 12 268 female cases. Adjusted for age and calendar year, men exposed to high levels of respirable crystalline silica compared with non-exposed showed increased incidence rate ratio (IRR) for the four diseases combined of 1.53 [95% confidence interval (CI): 1.39-1.69], for systemic sclerosis of 1.62 (1.08-2.44) and rheumatoid arthritis of 1.57 (1.41-1.75). The overall risk increased with increasing cumulative exposure attained since entering the workforce [IRR: 1.07 (1.05-1.09) per 50 µg/m3-years]. Female workers were less exposed to respirable crystalline silica, but showed comparable risk patterns with overall increased risk with increasing cumulative exposure [IRR: 1.04 (0.99-1.10) per 50 µg/m3-years]. CONCLUSIONS: This study shows an exposure-dependent association between occupational exposure to respirable crystalline silica and autoimmune rheumatic diseases and thus suggests causal effects, most evident for systemic sclerosis and rheumatoid arthritis.