Follow-up study of workers in a nylon carpet yarn plant after remedial actions taken against a contaminated humidification system

Objective: To investigate the effectiveness of remedial actions taken against a contaminated humidification system, after an outbreak of humidifier disease in a nylon carpet yam plant. Methods: Two and 6 years after modification, a follow-up investigation of a strati tied (age, smoking habits) sample of exposed (n = 75) and non-exposed (n = 56) workers was carried out. Outcome-parameters were. respiratory symptoms, spirometry, skin tests and serology with various humidifier fungi. In addition, the yearly incidence of work-disability because of chronic respiratory disease during the years before, and 11 years after the modification was compared. Results: At follow-up, exposed workers, who remained at the same workplace no longer had significantly more frequent chronic respiratory symptoms. The prevalence of positive serology was still higher (P <0.05) in exposed workers after 2 years, but at the 6 year follow-up investigation, the difference was no longer significant. Prevalence of positive skin tests after 2 years no longer differed from that of the non-exposed workers. Slopes (ml/years) of the graphs of forced vital capacity (FVC) and one-second forced expiratory volume (FEV1) during the 6 year follow-up after the first investigation did not differ between exposed and nonexposed workers, both before and after adjustment for age, smoking habits and results of skin tests and serology before modification. Before modification, exposed workers with a positive late skill test had a lower FVC than non-exposed workers. After 6 years of follow-up their FVC was still lower, but the difference was no longer significant. There were no indications of selective loss to follow-up. After remedial actions no new cases of humidifier disease occurred. Moreover, the yearly incidence of work-disability in this plant because of chronic respiratory disease, decreased from 1.30% to 0.27% compared with a decrease from 0.30% to 0.12% in other synthetic fibre plants. Conclusion: Follow-up investigation of exposure-effects demonstrated the effectiveness of remedial actions takes against a contaminated humidification system.