Occupational Exposure and 25-Year Incidence Rate of Non-Specific Lung Disease: The Zutphen Study

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Abstract
Information gathered in the Zutphen Study, the Dutch contribution to the Seven Countries Study that started in the 1960s, was used for the present study. In 1960 878 men participated in the physical examination and they were followed for 25 years until 1 July 1985. During this follow-up, their morbidity status was verified regularly. With this information the occurrence of chronic non-specific lung disease (CNSLD) at a specific time was coded by one physician, using strict criteria. The CNSLD diagnosis was based on the following criteria: —episodes of respiratory symptoms such as regular cough and phlegm for longer than three months or episodes of wheezing and shortness of breath reported to the survey physician, or: —diagnosis of CNSLD, including chronic bronchitis or emphysema by a clinical specialist. Occupation in 1960 was coded and used to generate specific occupational exposures with a Job Exposure Matrix. Because the exact time of diagnosis of CNSLD was known, incidence densities could be calculated. For 804 men a complete set of data was available. A Poisson regression analysis was used to analyse the relationships between the incidence density and independent variables like age, calendar period, occupation and specific occupational exposures. Blue collar workers had a significantly elevated incidence density ratio {IDR) compared to white collar workers (1.82, 95% confidence limits (CL): 1.35, 2.46). Subgroups of blue collar workers, wood and paper workers, textile workers, and tailors, construction workers and transport workers had significantly elevated IDRs also. Of the specific exposures heavy metals, mineral dust and adhesives had a significantly elevated IDR. Thirty per cent of the population had at least one exposure to dusts, fumes or gases in their occupation and they had a significantly elevated IDR of 1.4 compared to non-exposed workers (95% CL: 1.07, 1.85). These results are in concordance with a previous cross-sectional analysis of a sample of the Zutphen population and confirm the relationship between occupational exposures and CNSLD incidence.

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