Elsevier

The Lancet

Volume 370, Issue 9584, 28 July–3 August 2007, Pages 336-341
The Lancet

Articles
Exposure to substances in the workplace and new-onset asthma: an international prospective population-based study (ECRHS-II)

https://doi.org/10.1016/S0140-6736(07)61164-7Get rights and content

Summary

Background

The role of exposure to substances in the workplace in new-onset asthma is not well characterised in population-based studies. We therefore aimed to estimate the relative and attributable risks of new-onset asthma in relation to occupations, work-related exposures, and inhalation accidents.

Methods

We studied prospectively 6837 participants from 13 countries who previously took part in the European Community Respiratory Health Survey (1990–95) and did not report respiratory symptoms or a history of asthma at the time of the first study. Asthma was assessed by methacholine challenge test and by questionnaire data on asthma symptoms. Exposures were defined by high-risk occupations, an asthma-specific job exposure matrix with additional expert judgment, and through self-report of acute inhalation events. Relative risks for new onset asthma were calculated with log-binomial models adjusted for age, sex, smoking, and study centre.

Findings

A significant excess asthma risk was seen after exposure to substances known to cause occupational asthma (Relative risk=1·6, 95% CI 1·1–2·3, p=0·017). Risks were highest for asthma defined by bronchial hyper-reactivity in addition to symptoms (2·4, 1·3–4·6, p=0·008). Of common occupations, a significant excess risk of asthma was seen for nursing (2·2, 1·3–4·0, p=0·007). Asthma risk was also increased in participants who reported an acute symptomatic inhalation event such as fire, mixing cleaning products, or chemical spills (RR=3·3, 95% CI 1·0–11·1, p=0·051). The population-attributable risk for adult asthma due to occupational exposures ranged from 10% to 25%, equivalent to an incidence of new-onset occupational asthma of 250–300 cases per million people per year.

Interpretation

Occupational exposures account for a substantial proportion of adult asthma incidence. The increased risk of asthma after inhalation accidents suggests that workers who have such accidents should be monitored closely.

Introduction

Occupational asthma can be caused by more than 250 chemicals and about 15% of adult-onset asthma can be attributed to occupational exposure to pulmonary irritants.1, 2, 3, 4 Few such exposures have been assessed in prospective population-based studies designed to establish the incidence of asthma, rather than the cross-sectional prevalence.

Surveillance systems have played an important part in the identification of high-risk occupations and thus the prevention of occupational asthma. However the scope of these systems varies widely. Surveillance systems in the UK, USA, Australia, Belgium, and France each reported estimates of 20–40 new cases per million people every year, and higher estimates were recorded in British Columbia (Canada), Sweden, and Catalonia (Spain).5, 6, 7, 8, 9, 10, 11, 12 Finland has the highest estimate of all surveillance and reporting systems, at 174 cases per million people per year for 1989–95.13

Exposure-specific studies about occupational asthma have focused on substances, of high and low molecular-weight—eg, flour, enzymes, isocyanates, and latex.3, 14 Acute inhalation exposures are associated with reactive airways dysfunction syndrome.15, 16, 17 The population distribution of irritant-induced asthma and of asthma symptoms after inhalation accidents has thus far been investigated poorly.

A cross-sectional analysis of data from the European Community Respiratory Health Survey (ECRHS),18 an international population-based study done in 1990–95, noted increased odds ratios of asthma in several occupations, including farming, painting, and cleaning; the population attributable risk due to occupational factors was estimated as 9% of all cases of asthma in adults. Our follow-up ECRHS study was done about one decade later; we aimed to estimate the relative and attributable risks of new-onset asthma in relation to occupations, work-related exposures, and inhalation accidents.

Section snippets

Patients and procedures

Participants were 20–44 years of age at the time of ECRHS in 1990–95 and were randomly selected from the local populations of 28 centres in 13 countries. People who were included in ECRHS were recontacted and invited to take part in our follow-up survey (ECRHS-II) done in 1998–2003. Ethical approval was obtained for each centre from the appropriate institutional ethics committee, and written consent was obtained from each participant.

Complete occupational history between ECRHS and ECRHS-II was

Results

15 716 people took part in the original ECRHS study, of those 9175 responded to our ECRHS-II questionnaire. No differences were seen in the prevalence of occupational exposure associated with asthma risk at baseline between eligible people who responded and those who did not respond (p=0·54). Median time between completion of ECRHS and ECRHS-II was 8·9 years. 8476 participants took part in face-to-face interviews about occupational history; of these, 1639 were excluded because they had reported

Discussion

Our incidence data suggest that exposure to substances in the workplace causes more than 10% of all cases of adult-onset asthma. Occupations with the highest risk include nursing and cleaning. The highest risks were recorded for high-molecular-weight agents, but exposure to low-molecular-weight agents and irritants such as isocyanates, latex, and cleaning products also contribute substantially to the occurrence of occupational asthma.

Participants who had atopy at ECRHS and parental history of

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