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The Prevalence and Predictors of Respiratory-Related Work Limitation and Occupational Disability in an International Study^*

Paul D. Blanc, MD, FCCP; Peter Burney, MD; Christer Janson, MD and Kjell Torén, MD, PhD

^* From the Division of Occupational and Environmental Medicine (Dr. Blanc), Department of Medicine and the Cardiovascular Research Institute, University of California, San Francisco, CA; the Division of Primary Care and Public Health Sciences (Dr. Burney), Guy’s, King’s and St. Thomas’ School of Medicine, London, UK; Section of Respiratory Medicine and Allergology (Dr. Janson), Department of Medicine, Akademiska Sjukhuset, Uppsala University, Uppsala, Sweden; and the Department Respiratory Medicine and Allergology (Dr. Torén), Sahlgrenska University Hospital, Göteborg, Sweden. A list of the principal participants of the ECRHS study is located in the ^Appendix.

Correspondence to: Paul D. Blanc, MD, FCCP, Occupational and Environmental Medicine, UCSF, 350 Parnassus Ave, No. 609, San Francisco, CA 94117; e-mail: blancp{at}itsa.ucsf.edu

	Abstract

TOP Abstract Introduction Materials and Methods Results Discussion Appendix References

 
Background: Work-related symptoms and disability due to respiratory disease are common and costly among working-age adults. To investigate this problem, we analyzed data on respiratory symptoms related to the workplace and occupational disability from the European Community Respiratory Health Survey (ECRHS).

Methods: The ECRHS is a population-based sample of adults aged 20 to 44, with oversampling of subjects with symptoms that are consistent with respiratory disease. We analyzed structured interviews from 17,567 subjects, of whom 15,039 were from a general random population sample and 2,528 were from the respiratory symptom oversample. We defined work-related respiratory symptoms as self-reported wheeze or chest tightness at work, and work-related respiratory disability as reported job change due to breathing difficulties at work. We used binary generalized linear modeling with a log link to estimate the risk of symptoms and disability.

Findings: Wheeze at work was reported in the general population sample by 1,552 subject (10%), ranging from 4 to 15% among the 16 countries analyzed. Work-related respiratory disability was reported by 540 subjects (4%), ranging from 1 to 8%. Reported workplace exposure to vapors, gases, dust, or fumes was associated with increased risk of respiratory symptoms at work (prevalence ratio [PR], 2.1; 95% CI 1.8–2.4) and work-related respiratory disability (PR, 3.4; 95% confidence interval [CI], 2.0 to 5.1). Workplace environmental tobacco smoke exposure was associated with symptoms (PR, 1.3; 95% CI, 1.2 to 1.5) but not with disability (PR, 1.1; 95% CI, 0.9 to 1.4).

Interpretation: These data indicated that work-related respiratory symptoms and disability vary widely in this international sample but, nonetheless, are associated with workplace exposures that could be addressed through preventive measures.

Key Words: asthma • occupational health • respiratory disease • wheeze • work disability

	Introduction

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Work disability due to lung disease is common and costly. This problem stems from the prevalence of lung disease, especially asthma, among adults of working age.¹ Even upper respiratory tract complaints that are generally considered to be nondisabling, such as allergic rhinitis, may be associated with prominent decrements in work productivity.²

The origins of workplace disability are multifactorial and reflect an interaction between a person with a health condition causing an impairment and the environment, which may induce or aggravate symptoms and limit functional ability.³ Occupational conditions comprise a critical component of this environment. Exposure to irritants, dusts, or other adverse conditions that are known or suspected to cause or aggravate respiratory disease might be expected to promote disability as well. In occupational terms, the most severe manifestation of disability is the complete cessation of employment. Short of this, there are a number of other important measures of occupational disability, including lost work days, change in employment, limitation in duties, or reduction in the number of work hours due to ill health.

We used data from an international study of lung disease among adults of working age, the European Community Respiratory Health Survey (ECRHS), to analyze the impact of workplace exposures on respiratory symptoms at work and on reported changes in job due to breathing difficulty, which we used as a measure of occupational disability. We were particularly interested in this question because of an earlier analysis of ECRHS data from Sweden⁴ that had indicated such occupational disability was common and was related to working conditions. We hypothesized that this association would be consistent internationally over a range of potential exposures.

	Materials and Methods

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Overview
We analyzed data that had been collected previously through the ECRHS. The overall study design has been detailed in previous publications.^{5 6 7} In brief, the data were obtained through a two-step survey design based on a random population sample carried out by each participating study center. In the initial sampling step, adult subjects aged 20 to 44 years were asked to complete a brief, self-administered screening questionnaire.

The second stage of the survey was based on a subsample of the initial study group who completed the more extensive questionnaire that forms the basis of this analysis. There were two sampling frames used for this stage. In the main sampling frame, a random sample approximating 20% of the initial screening questionnaire group was selected. An additional sampling frame was intended to enrich the study population for adults with asthma by preferentially recruiting subjects who responded affirmatively to at least one of a series of three asthma-related questions from the initial screening questionnaire. Although subjects who completed the second-stage questionnaire were also eligible to undergo allergen skin prick testing and pulmonary function testing, the analysis for the current study is limited to questionnaire data only.

The international data coordinating center for the ECRHS currently manages a data set for participating centers from 19 different countries worldwide. Data for this analysis were made available through one of the participating centers (Göteborg, Sweden), through which local approval for research involving human subjects is maintained.

Questionnaire Format and Content
The questionnaire was designed to be administered face-to-face but was completed by telephone interview for some subjects in certain centers. The study questionnaire included items covering chronic bronchitis symptoms (defined as productive winter cough for 3 months each year), asthma and atopy history (defined by self-report of the condition with or without a reported physician’s diagnosis; for atopy this was asked about in the form of nasal allergies including hay fever), smoking (defined as 20 packs smoked in a lifetime), exposure to environmental tobacco smoke (ETS) [by self report], and occupation.⁸

All subjects were asked whether or not they were full-time students. Only those who were not full-time students then were asked a series of occupational items. These included the questions "Does being at work ever make your chest tight or wheezy?" and "Do people smoke regularly in the room where you work?" We used this latter question to define workplace ETS exposure.

The current job or most recent job was ascertained as well. Although other prior employment was not systematically ascertained, two questions elicited prior occupations. These questions were "Have you ever had to change or leave your job because it affected your breathing?" and "Have you ever worked in a job which exposed you to vapors, gas, dust or fumes?" In each case, respondents were asked to specify the job involved.

Occupation was collected in an open-ended format that was later coded using the European Commission Alphabetical Index for Classifying Occupations.⁹ This 3-digit coding scheme allows for 348 different occupations and two additional classifications, "inadequately described occupations" and "occupations not stated, including housewife and student."

Interview-Derived Occupational Exposure Measures
We used a hierarchical approach to identify subjects’ employment. We used a job exposure matrix (JEM) to assign the likelihood that such employment involved exposures to inhalants associated with greater respiratory risk, particularly for causing asthma.⁴ For this analysis, we preferentially assigned to respondents the occupation that reportedly caused them to change jobs because it affected their breathing. If no such change was reported, but a job involving exposure to vapors, gas, dust, or fumes (VGDF) was noted, this was the occupation that was assigned to the subject for the purposes of the JEM. If there was no such reported exposure, we used the current or most recent occupation reported by the respondent for the JEM. The JEM included 348 distinct occupational codes.⁴ We categorized each respondent’s occupation as being of low, intermediate, or high respiratory exposure likelihood. Examples of intermediate occupations included nurses (potential latex exposure), photographers (exposure to reactive chemicals and metal salts), garage proprietors (exposure to diesel exhaust), and printers (exposure to inks and other chemicals). High-risk occupations included farmers (exposure to organic dusts), firefighters (exposure to combustion byproducts), bakers (exposure to flours and enzymes), spray painters (exposure to isocyanates), and carpenters (exposure to wood dusts). Occupations with low exposure likelihood included administrators, teachers, accountants, clerks, and secretaries.

Defining Work-Related Respiratory Symptoms and Disability, and Other Limitations
We defined work-related respiratory symptoms by the survey question "Does being at work ever make your chest tight or wheezy?" We defined work-related respiratory disability by the question, "Have you ever had to change or leave your job because it affected your breathing?" Finally, we defined nonrespiratory, non-work-related limitation with the question, "Are you disabled from walking by a condition other than heart or lung disease?"

Study Inclusion and Exclusion Criteria
We limited eligibility to ECRHS centers that had provided occupational coding at the 3-digit level to the international data set and had included all of the occupational questions of study interest in their local version of the questionnaire. The centers that did not meet these inclusion criteria were from France, the Netherlands, and Switzerland. There were 21,016 subjects in the data set from 16 different countries eligible for study. Because neither present nor past occupational data were available for full-time students, we excluded these from analysis (1,632 subjects; 7.8%), along with those with no history of labor force participation noted (562 subjects; 2.7%). We also excluded 659 subjects (3.1%) for whom the vocational data were coded as "housewife or not elsewhere classified." Finally, we excluded another 596 subjects (2.8%) who were missing other key data. After all exclusions, 17,567 subjects remained for analysis, comprising 84% of the initial subject pool.

Statistical Analysis
We performed analyses using a standard statistical software package (SAS; SAS Institute; Cary, NC). We tested differences between groups using the ² test or t test. We used the Spearman correlation to test the rank order of symptom disability rates by survey country. To test the association between occupational factors and wheeze at work and change of work due to breathing difficulties, we employed a binary generalized linear model with a log link to estimate prevalence ratios (PRs), including smoking status, age, and gender as fixed-effect covariates. In these analyses, the potential statistical impact of clustering by country of residence was taken into account in estimating the variance of parameter estimates using an approach analogous to a repeated measures technique.¹⁰

	Results

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Of the 17,567 subjects included in this analysis, 15,039 (86%) were derived from the general sample without regard to respiratory status, while 2,528 (14%) were selected as part of the supplemental sample because of respiratory symptoms or conditions elicited at the time of initial interview.

More than half of all subjects reported workplace exposure to VGDF (Table 1 ), although the frequency of categorization in a high likelihood of exposure occupation by JEM was lower, at 15% overall. Consistent with an association between exposure and respiratory disease, the general sample and the symptom-enriched supplemental sample differ systematically from each other in these work-related variables, as well as in smoking and demographics. We used the stratum of subjects who were selected for interview independently of symptom reporting to estimate the population-based frequencies of work-related respiratory symptoms (ie, wheeze at work) and disability (ie, job change attributed to breathing difficulties). For risk estimates combining both strata, we adjusted for demographic variables.

We used generalized estimating models to test an explanatory model of wheeze associated with the workplace and change of job due to respiratory symptoms, taking into account clustering at the level of country of study (Table 3 ). For these models, we used both ECRHS sampling frames (17,567 subjects), including in the same model all of the covariates that are listed in Table 1 .

Current active cigarette smoking, past smoking, and ETS exposure were all associated with a similar risk for wheeze at work (PR range, 1.1 to 1.3; p < 0.01 in all cases). In contrast, only ex-smoking was associated with a statistically significant risk of job change due to breathing difficulties (PR, 1.2; 95% CI, 1.01 to 1.4).

We retested the same risk factors for wheeze at work and for job change, stratifying by age 33.7 vs >33.7 years (the mean of the group), by gender, and by atopic disease being reported (9,513 subjects) or not reported (8,054 subjects). There were no substantive differences in the patterns of risk associated either with self-reported exposure to VGDF or to exposure based on risk classification using the JEM.

Although the ECRHS did not directly ascertain complete cessation of work attributed to respiratory symptoms, we indirectly estimated this through the prevalence of subjects who reported a prior job change due to breathing difficulties and who also were not currently employed at the time of interview. Of 773 subjects reporting breathing-related job change from the entire survey sample (17,567 subjects), 156 (20.2%; 95% CI, 17.4 to 23.0%) were no longer employed at the time of the interview. Their rate of unemployment is significantly higher than the rate of 13% reported by all other respondents in the survey (p < 0.001).

We analyzed the prevalence of job change attributed to breathing problems in relation to the prevalence of various respiratory tract and atopic conditions reported by survey respondents (Fig 1 ). For each of the group of conditions, the prevalence of respiratory-related work disability was significantly greater than for those without any of the conditions analyzed. Altogether, 396 of 3,786 subjects (11%) reporting either asthma or chronic bronchitis also had reported a job change due to breathing difficulties. Job change was reported by 549 of 9,513 subjects (6%) with nasal or skin allergies. Among those without such conditions, the rate was < 3%.

View larger version (28K): [in this window] [in a new window] [Download PPT slide]   Figure 1.. Frequency of job change attributed to breathing problems among those with and without selected health conditions. Top, A: asthma and chronic bronchitis. Bottom, B: nasal and skin allergies.

	Discussion

TOP Abstract Introduction Materials and Methods Results Discussion Appendix References

This analysis also indicated that occupational conditions are themselves important contributors to job change that is attributable to shortness of breath in the workplace. Those reporting workplace exposures to VGDF were nearly four times as likely to change jobs due to symptoms. In multivariable modeling, higher exposure occupations that were classified on the basis of a JEM also appeared to carry independent risk. A similar pattern of occupational exposure risk factors also was linked to self-reported wheeze at work, a far more common impairment than job change. ETS exposure at work was an exception, demonstrating increased risk for wheeze at work, but not for job change due to breathing trouble.

There is no direct equivalence between subjective symptoms and loss of work. There was a striking international variation by country of residence for both job change attributed to breathing problems as well as for nonrespiratory, non-work-related disability (ie, limitations in walking other than from cardiopulmonary disease). Perhaps this degree of variation should be anticipated. The sources of variability in job change due to breathing could include working conditions, job market pressures, national norms of job stability, and differing social policies. Specific research would be needed to assess these speculative factors as drivers of international variation change in job attributed to breathing difficulties.

Simplistic cross-cultural explanations of variation, such as a greater propensity to report disability of any kind, is inconsistent with the poor, nearly inverse correlation in ranking for reported respiratory disability compared to noncardiopulmonary disability, which we analyzed as a generic, nonoccupational benchmark condition. In contrast, despite economic and compensation factors among varying countries that might have uncoupled the reporting of respiratory symptoms at work from respiratory-related job changes, the ranks of the two frequencies correlated fairly closely. In certain cases, questionnaire translation also may have contributed variation, particularly in the case of Germany where the reported rate of noncardiopulmonary walking limitation was highest. In that specific case, the German-language translation that was used may be closer to "difficulty" than to "limitation," (Dr. Katja Radon; personal communication; November 12, 2002). Even among the predominantly English-speaking countries in the survey, however, the noncardiopulmonary disability rate varied from 0.2% (United States rank, 16) to 4.3% (New Zealand rank, 10).

Our data have important limitations. Job change attributed to breathing difficulties, which we used as a surrogate of respiratory occupational disability, was based on self-reports. The survey did not independently collect and validate employment data nor did it specifically assess the complete cessation of employment for health-related reasons. Similarly, exposure to VGDF also is based on self-report, although this or similar measures have been used in a number of other surveys and have been shown to predict increased respiratory symptoms or lung function decrements.^{16 17 18 19 20 21} Moreover, we also used an alternative and independent measure of exposure through a JEM.

Due to missing work-related variables, we excluded several important groups of subjects, most notably ECRHS data from France, the Netherlands, and Switzerland. In addition, we also excluded subjects within a category of work status within the ECRHS which includes, but is not limited to, housewives. Thus, we cannot assess disability in association with this nonsalaried vocation.

Another study limitation may arise in analyzing the ECRHS data at the level of country of residence, rather than at the level of participating center within each country. In the ECRHS, the number of participating centers varied from one center per country (ie, United States, Denmark, Iceland, Norway, Australia, Estonia, and Poland) up to a maximum of six centers (ie, Canada and Spain). This could have introduced clustering effects. Although we derived our estimates of wheeze at work and job change from the sample that was not enriched for those likely to have respiratory disease, we did use the entire sample in our risk estimates. Doing this increased study power by providing more persons with adverse outcomes but may have impacted external validity. In terms of international extrapolation, developing economies with large, occupationally exposed populations are not represented in this analysis. Finally, it should be kept in mind that this was a cross-sectional analysis in which exposure and job change were ascertained in retrospect. Longitudinal follow-up from the ECRHS now in progress may help to better elucidate the relationships of workplace exposures to respiratory symptoms, impairment, and disability.

In summary, these survey data indicate that work-related respiratory symptoms and disability vary widely. Yet, taken as a whole, this problem is common internationally and has an important exposure-related component in the workplace. Because workplace exposures are subject to control interventions, this source of morbidity and disability is an important potential target for prevention strategies.

	Appendix

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Principal Participants in the ECRHS Study
Coordinating Centre (London, UK): P. Burney, S. Chinn, C. Luczynska, D. Jarvis, and E. Lai; Australia: M. Abramson and J. Kutin (Melbourne); Belgium: P. Vermeire, and F. van Bastelaer (Antwerp South and Antwerp Central); Canada: M. Chan-Yeung, H. Dimich-Ward (Vancouver), J. Manfreda, N.R. Anthonisen (Winnipeg), M.R. Sears, H.C. Siersted (Hamilton), M.R. Becklake, P. Ernst (Montreal), D.M. Bowie (Halifax), L.E. Sweet, and L. Van Til (Prince Edward Island); France: J. Bousquet (Montpellier), F. Neukirch, R. Liard (Paris), I. Pin, C. Pison (Grenoble), and A. Taytard (Bordeaux); Estonia: R. Jogi (Tartu); Germany: H. Magnussen, D. Nowak (Hamburg), H.E. Wichmann, and J. Heinrich (Erfurt); Iceland: T. Gislason and D. Gislason (Reykjavik); Ireland: J. Prichard, S. Allwright, and D. MacLeod (Dublin); Italy: M. Bugiani, C. Bucca, C. Romano (Turin), R. de Marco, V. Lo Cascio, C. Campello (Verona), A. Marinoni, I. Cerveri, and L. Casali (Pavia); Netherlands: B. Rijcken and A. Kremer (Groningen, Bergen-op-Zoom, Geleen); New Zealand: J. Crane and S. Lewis (Wellington, Christchurch, Hawkes Bay); Norway: A. Gulsvik, E. Omenaas, and C. Svanes (Bergen); Spain: J. Antó, J. Sunyer, J. Soriano, A. Tobías, J. Roca, M. Kogevinas (Barcelona), N. Muniozguren, J. Ramos González, A. Capelastegui (Galdakao), J. Martinez-Moratalla, E. Almar (Albacete), J. Maldonado, A. Pereira, J. Sánchez (Huelva), F. Payo, and I. Huerta (Oviedo); Sweden: G. Boman, C. Janson, E. Bjornsson (Uppsala), L. Rosenhall, E. Norrman, B. Lundback (Umea), N. Lindholm, and P. Plaschke (Göteborg); Switzerland: U. Ackermann-Liebrich, N. Künzli, and A. Perruchoud (Basel); United Kingdom: M. Burr, J. Layzqll (Caerphilly), R. Hall (Ipswich), B. Harrison (Norwich), and J. Stark (Cambridge); United States: S. Buist, W. Vollmer, and M. Osborne (Portland).

	Acknowledgements

 
We are grateful to Colette Baya and Dr. Manuel Hallen for their help during the study and to Professor K. Vuylsteek and the members of the Comité d’Action Concerte (European Union) for their support.

	Footnotes

 
Abbreviations: CI = confidence interval; ECRHS = European Community Respiratory Health Survey; ETS = environmental tobacco smoke; JEM = job exposure matrix; PR = prevalence ratio; VGDF = vapors, gas, dust, or fumes

The coordination of this work was supported by the European Commission. The following grants helped to fund the local studies whose data was included in this analysis: Australia: Allen and Hanbury’s, Australia; Belgium: Belgian Science Policy Office and the National Fund for Scientific Research; Canada: Health Canada, Glaxo Canada, and Province of Prince Edward Island; Estonia: The Estonian Scientific Foundation (grant 1088) and Glaxo Welcome; Germany: Gesellschaft für Strahlen-und Umweltforschung and the Bundesminister für Forschung und Technologie, Bonn; Ita1y: Ministero dell’Università e della Ricerca Scientifica e Tecnologica, Consiglio Nazionale delle Ricerche, Regione Veneto grant Rícerca Sanitaria Fínalizzata No. 381/05.93; New Zealand: Asthma Foundation of New Zealand, Lotteries Grant Board, and the Health Research Council of New Zealand; Norway: Norwegian Research Council project No. 101422/310; Spain: Ministero Sanidad y Consumo Fondo de Investigaciones Sanitarias grants No. 91/0016060/00E-05E, 92/0319, and 93/0393, Hospital General de Albacete, Hospital General Juan Ramón Jiménez, and Consejeria de Sanidad Principado de Asturias; Sweden: The Swedish Heart Lung Foundation, the Swedish Medical Research Council, and the Swedish Association against Asthma and Allergy; United Kingdom: National Asthma Campaign, British Lung Foundation, Department of Health, and the South Thames Regional Health Authority; and United States: US Department of Health and Human Services, Public Health Service grant No. 2 S07 RR05521-28. The research for this article was supported in part by the Swedish Council for Worklife Research (Dr. Torén), Swedish Medical Research Council, the Swedish Heart and Lung Foundation, and the Swedish Association Against Asthma and Allergy.

Received for publication October 14, 2002. Accepted for publication January 8, 2003.

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