Asthma incidence in wood-processing industries in Finland in a register-based population study.

Objectives: This register-based population study determined incidence rates of clinically verified asthma among woodworkers, other blue-collar workers, and administrative personnel employed in wood-processing industries in Finland. Exposure to wood dust was under special scrutiny.

Methods: All Finns employed in wood-processing industries were followed for asthma incidence via record linkage in the years 1986-1998. Incident cases included people with asthma reimbursed for medication by the national health insurance or registered as having occupational asthma. Age-adjusted incidence rates and relative risks (RR) by gender were estimated for wood workers, other blue-collar workers, and administrative employees (referents) in wood industries.

Results: The relative risk of asthma was increased for all woodworkers among both genders [men: RR 1.5, 95% confidence interval (95% CI) 1.2-1.8; women: RR 1.5, 95% Cl 1.2-1.7]; a similarly elevated risk was also found for other blue-collar workers (men: RR 1.5, 95% Cl 1.2-1.8; women: RR 1.4, 95% Cl 1.2-1.6) in the same wood industries. Statistically increased relative risks were found for low and medium exposure to wood dust, but not for high exposure. Altogether 217 of the 4074 clinically verified asthma cases were reported as occupational asthma in the Finnish Register on Occupational Diseases.

Conclusions: The incidence rates for asthma were significantly increased both among the woodworkers and the other blue-collar workers in wood industries but without a clear dose-response. Cases recognized as occupational asthma accounted for only a small part of the total asthma excess, indicating that much of the work-related asthma excess remains unrecognized in these industries.