Work-related asthma in Montreal, Quebec: population attributable risk in a community-based study.

BACKGROUND: Occupational exposures are an important cause of adult-onset asthma but the population attributable risk percentage (PAR%) has been less frequently studied. OBJECTIVES: To examine the distribution and determinants of adult asthma in six centres across Canada using data gathered in a community-based study. METHODS: Data were gathered in a community survey of 2959 adults using the European Community Respiratory Health Survey Protocol. A subsample of 498 subjects completed detailed health and occupational questionnaires, methacholine challenge tests and allergy skin tests. Asthma was defined in three ways: current wheeze, asthma symptoms and/or medication, and airway hyperresponsiveness. Occupational exposures were classified as sensitizers or irritants. Associations between asthma and occupational exposures were examined using logistic regression analysis. Model selection was based on the findings for current wheeze, and the same model was applied to the other definitions of asthma. RESULTS: Fifty-six per cent of subjects reported ever having had occupational exposure to sensitizers, and 9.8% to irritants. Current wheeze was associated with exposure to irritants (PAR% 4.54%), and airway hyperresponsiveness was associated with exposure to sensitizers (PAR% 30.7%). Neither a history of childhood asthma, atopy, nor confining the analysis to adult-onset asthma affected these associations. Analysis of effect modification suggested two types of work-related asthma: one due to exposure to occupational sensitizers, and the other due to exposure to irritants. CONCLUSIONS: Detailed assessment of past and current exposures is essential in the investigation of work-related asthma. Childhood asthma reactivated or aggravated by work exposures is not easy to distinguish from asthma induced by work, a misclassification that could lead to an underestimation of work-induced asthma. This should be taken into account in jurisdictions in which persons with work-aggravated asthma are not eligible for workers' compensation.

Cross-shift peak expiratory flow changes are unassociated with respirable coal dust exposure among South African coal miners.

BACKGROUND: The objectives of this study were to determine whether cross-shift changes in peak expiratory flow rate (PEFR) were related to respirable dust exposure in South African coalminers. METHODS: Fifty workers were randomly selected from a cohort of 684 miners from 3 bituminous coalmines in Mpumalanga, South Africa. Peak expiratory efforts were measured prior to the commencement of the shift, and at the end of the shift on at least two occasions separated by at least 2 weeks, with full shift personal dust sampling being conducted on each occasion for each participant. Interviews were conducted, work histories were obtained and cumulative exposure estimates were constructed. Regression models examined the associations of cross-shift changes in PEFR with current and cumulative exposure, controlling for shift, smoking and past history of tuberculosis. RESULTS: There were marginal differences in cross-shift PEFR (ranging from 0.1 to 2 L/min). Linear regression analyses showed no association between cross-shift change in PEFR and current or cumulative exposure. The specific shift worked by participants in the study showed no effect. CONCLUSIONS: Our study showed no association between current respirable dust exposure and cross-shift changes in PEFR. There was a non-significant protective effect of cumulative dust exposure on the outcome, suggesting the presence of a "healthy worker survivor effect" in this data.

Airflow obstruction in young adults in Canada.

OBJECTIVE: Airflow obstruction is relatively uncommon in young adults, and may indicate potential for the development of progressive disease. The objective of the present study was to enumerate and characterize airflow obstruction in a random sample of Canadians aged 20 to 44 years. SETTING: The sample (n=2962) was drawn from six Canadian sites. DESIGN: A prevalence study using the European Community Respiratory Health Survey protocol was conducted. Airflow obstruction was assessed by spirometry. Bronchial responsiveness, skin reactivity to allergens and total serum immunoglobulin E were also measured. Logistic regression was used for analysis. RESULTS: Airflow obstruction was observed in 6.4% of the sample, not associated with sex or age. The risk of airflow obstruction increased in patients who had smoked and in patients who had lung trouble during childhood. Adjusted for smoking, the risk of airflow obstruction was elevated for subjects with past and current asthma, skin reactivity to allergens, elevated levels of total immunoglobulin E and bronchial hyper-responsiveness. Of the subjects with airflow obstruction, 21% were smokers with a history of asthma, 50% were smokers without asthma, 12% were nonsmokers with asthma and 17% were nonsmokers with no history of asthma. Bronchial hyper-responsiveness increased the prevalence of airflow obstruction in each of these groups. CONCLUSION: Smoking and asthma, jointly and individually, are major determinants of obstructive disorders in young adults. Bronchial hyper-responsiveness contributes to obstruction in both groups.

Respirable coal dust exposure and respiratory symptoms in South-African coal miners: a comparison of current and ex-miners.

OBJECTIVES: Dose-response associations between respirable dust exposure and respiratory symptoms and between symptoms and spirometry outcomes among currently employed and formerly employed South-African coal miners were investigated. METHODS: Work histories, interviews, and spirometry and cumulative exposure were assessed among 684 current and 212 ex-miners. RESULTS: Lower prevalences of symptoms were found among employed compared with ex-miners. Associations with increasing exposure for symptoms of phlegm and past history of tuberculosis were observed, whereas other symptom prevalences were higher in the higher exposure categories. Symptomatic ex-miners exhibited lower lung function compared to the nonsymptomatic. CONCLUSIONS: Compared with published data, symptoms rates were low in current miners but high in ex-miners. Although explanations could include the low prevalence of smoking and/or reporting/selection bias, a "survivor" and/or a "hire" effect is more likely, resulting in an underestimation of the dust-related effect.

Childhood predictors of smoking in adolescence: a follow-up study of Montreal schoolchildren.

BACKGROUND: The factors that cause children to become smokers in adolescence remain unclear. Although parental smoking and peer pressure may play a role, physiological factors such as lung volume have also been identified. METHODS: To investigate these and other possible childhood predictors of teenage smoking, we gathered follow-up data on 191 Montréal schoolchildren, aged 5-12 years (average 9.2 yr) when first examined. At an average age of 13.0 years, they answered further questions on their health and smoking behaviour and provided a second set of spirometric measurements. RESULTS: At the second survey, 80% of the children had entered high school and 44% had become smokers. Reaching puberty between the surveys was the most significant determinant of becoming a smoker: 56.4% of the 124 children postpubertal at the second survey had taken up smoking, versus 17.9% of the 67 who were still prepubertal (p = 0.001). We found salivary cotinine level, a measure of uptake of environmental tobacco smoke, to be an independent predictor of becoming a teenage smoker; even after adjustment for sex, socioeconomic status of parents, a crowding index, and the numbers at home of siblings, adult smokers and cigarettes smoked, it remained significant for both groups: postpubertal (odds ratio [OR] 1.2, 95% confidence interval [CI] 1.2-3.0) and prepubertal (OR 2.1, 95% CI 1.0- 4.5). The influence of forced vital capacity was marginally significant only in the postpubertal group (OR 5.0, 95% CI 0.88-28.3). INTERPRETATION: The proportion of nicotine absorbed from that available in environmental tobacco smoke during childhood is associated with subsequent smoking in adolescence. The more efficient absorption of nicotine seen in some children may be related to physiological factors such as lung capacity.

Differential respirable dust related lung function effects between current and former South African coal miners.

Dust-related dose-response decrements in lung function among coal miners have been reported in several studies, with varying magnitudes across populations. Few studies have compared differences between current and former coal miners. No studies on dose response relationships with lung function have been conducted in South African coal mines, one of the top three producers of coal internationally. The objectives of this study were (1) to describe the relationship between respirable dust exposure and lung function among current and former South African coal miners and to determine whether differential dust related effects were present between these employment categories; (2) to examine dust related dose response relationships, controlling for potential confounding by smoking and a history of tuberculosis (TB). Six hundred and eighty-four current and 188 ex-miners from three bituminous coal mines in Mpumalanga Province were studied. Interviews assessing work histories, smoking profiles and other risk factors were conducted. Work histories were also obtained from company records. Standardised spirometry was performed by trained technicians. Cumulative respirable dust exposure (CDE) estimates were constructed from company-collected sampling and measurements conducted by the researchers. Regression models examined the associations of CDE with per cent predicted FEV(1) and FVC, controlling for smoking, past history of TB and employment status. A statistically significant decline in FEV(1) of 1.1 and 2.2 ml/mg-year/m(3) was found in representative 40-year-old, 1.7-m tall current and former miners, respectively. Significant differences were found between the highest and medium exposure categories. Ex-miners had a lower mean per cent predicted lung function than current miners for each cumulative exposure category, suggesting a "healthy worker" effect. Past history of TB contributed to 21 and 14% declines in per cent predicted FEV(1) and FVC, respectively. Thus, in this cohort, a dose-related decline in lung function was associated with respirable dust exposure, with a magnitude of effect similar to that seen in other studies and important differences between current and former employees. A "healthy worker" effect may have attenuated the magnitude of this relationship. TB was a significant contributor to lung function loss.

Discordance between cross-sectional and longitudinal studies for the effect of dust on COPD: why?

Regression analyses for the effect of an environmental agent on lung function often give discordant results when derived from cross-sectional compared with longitudinal studies. To evaluate why this occurs, a normal population was created by computer, and modeled to simulate functional change during life. Thus, factors known to influence lung function measurement (including those that may cause COPD) were manipulated experimentally so that their contributions to any discordance could be assessed. Regression analyses showed that significant discordance could be induced if the oldest birth cohort failed to reach the same maximal level of function as the youngest (a "cohort effect"). This distorted the cross-sectional (but not longitudinal) estimate for the dominating effect of age and additionally influenced cross-sectional estimates for the effects of partially collinear variables such as cumulative exposure to hazardous environmental dust. Discordance also occurred if regression coefficients became imprecise through random measurement/reporting error, between-subject variability, and differing susceptibility, but then the differences (sometimes marked) between cross-sectional and longitudinal estimates were not significant. We conclude that modeling a population with known characteristics can provide a useful means of demonstrating that cross-sectional versus longitudinal discordance may be fundamental and unavoidable (though explicable), or merely a consequence of imprecision.

Geographic and gender variability in the prevalence of bronchial responsiveness in Canada.

OBJECTIVES: Geographic variability in reported prevalences of asthma worldwide could in part relate to interpretation of symptoms and diagnostic biases. Bronchial responsiveness measurements provide objective evidence of a common physiologic characteristic of asthma. We measured bronchial responsiveness using the standardized protocol of the European Community Respiratory Health Survey (ECRHS) in six sites in Canada, and compared prevalences across Canada with international sites. DESIGN: Samples of 3,000 to 4,000 adults aged 20 to 44 years were randomly selected in Vancouver, Winnipeg, Hamilton, Montreal, Halifax, and Prince Edward Island, and a mail questionnaire was completed by 18,616 individuals (86.5%). Preselected random subsamples (n = 2,962) attended a research laboratory for examination including more detailed questionnaires, lung function testing including methacholine challenge, and skin testing with 14 allergens. RESULTS: Prevalences of bronchial hyperresponsiveness, measured as cumulative dose of methacholine required to produce a 20% fall from the post-saline solution FEV1 < or = 1 mg, ranged from 4.9% (95% confidence interval [CI], 1.6 to 8.5) in Halifax to 22.0% (95% CI, 18.1 to 26.0) in Hamilton (median, 10.7%). In all Canadian sites, bronchial hyperresponsiveness was more prevalent in women than in men. Neither the geographic nor gender differences were accounted for by differences in age, smoking, skin test reactivity, or baseline FEV1. Geographic- and gender-related variability changed little when only bronchial hyperresponsiveness associated with asthma-like symptoms was considered. CONCLUSIONS: A wide variability in bronchial responsiveness can occur within one country, almost as wide as the range found across all international sites participating in the ECRHS study and not explained by differences in gender, smoking, skin test reactivity, and FEV1. While gender variability in the prevalence of bronchial responsiveness is likely due to hormonal and immunologic factors, geographic variability is likely to result from environmental factors.

Healthy worker effect in cohort studies on chronic bronchitis.

OBJECTIVES: Despite the recognition of selection biases arising from the healthy worker effect in occupational mortality studies, the possibility of similar effects in occupational cohort studies on respiratory symptoms is not well known. Two mechanisms are responsible for the healthy worker effect in respiratory cohort studies. One is health-based selection of workers into employment (healthy him effect), and the other is health-based differential losses to follow-up (healthy worker survivor effect). The aim of the present paper was to estimate the magnitude of the healthy worker survivor effect in cohort studies of symptoms of chronic bronchitis. METHODS: A meta-analysis of occupational cohort studies of symptoms of chronic bronchitis was performed that included published articles identified in searches of the Medline bibliographic databases between 1980 and March 2001 and the reference lists of the located articles. RESULTS: Eight cohort studies were identified using an a priori selection criterion. The pooled odds ratio of the prevalence of chronic bronchitis for subjects leaving the cohorts was 1.23 when these subjects were compared with those who remained under study (95% confidence interval 1.04-1A4). CONCLUSIONS: The prevalence of respiratory symptoms among exposed workers may he underestimated if the healthy worker survivor effect is not taken into account