Isocyanate-induced asthma is the most prevalent occupational asthma in Korea. The main purpose of this study was to estimate the etiologic fraction of isocyanate-related asthma in isocyanateexposed (EFe) workers and to measure the magnitude of preventable occupational asthma.

Asthma admissions from 2000 to 2005 were analyzed in a cohort containing 10,861 isocyanate-exposed workers and 324,618 isocyanate non-exposed workers who underwent the specialized health examination from January, 2000 to December, 2004. The cohorts of Isocyanate and noise-exposed workers were established using the same data base of Korea Occupational Safety and Health Agency (KOSHA). Asthma admissions were investigated by matching the National Health Insurance Claim Data (NHICD). The standardized rate ratio (SRR) of admission was estimated by Poisson regression method to allow unbiased comparisons across exposure and other variables such as age and sex. The etiologic fraction for the isocyanate-exposed (EFe) workers was calculated using this formula (Efe=SRR-1/SRR).

Twenty-eight asthma admissions among the isocyanate-exposed workers and 321 non-exposed workers were observed during 2000~2005. The crude admission rate was 57.2 per 100,000 person-years for the isocyanate-exposed workers and 25.0 for the noise-exposed workers. Compared to the noiseexposed workers, the isocyante-exposed workers had significantly higher asthma admission (SRR=2.80 95%CI=1.89~4.14). The etiologic fraction for the isocyanate-exposed (EFe) workers was 64%.

This study was limited by the restriction to admission cases and the short follow-up periods. Any difference of admission accessibility between the isocyanate-exposed and non-exposed workers will lead to either over- or under-estimation of the biased etiologic fraction for the isocyanateexposed workers. The etiologic fraction for the isocyanate-exposed workers was 64% indicated that 64% of the asthma cases occurred in the isocyanate-exposed workers are preventable through occupational health management.