Introduction and objectives:
Microbiological control agents (MBCA) are widely used in greenhouses, replacing chemical pesticides. The presented study aims to describe health effects of exposure to three types commonly used: Bacillus thuringiensis, Verticillium lecanii, and Trichoderma harzenianum covering seven different products in greenhouse workers with emphasis on sensitization and respiratory effects.

Methods:
579 persons aged 17-67 years culturing ornamental flowers were included. They were followed for three years with annual examinations including interview about exposure and symptoms, lung function, including bronchial (histamine) challenge test, and blood samples. Direct and indirect exposure for each person and year was estimated by information from respondents and employers. IgE in serum against the 7 products of MCBA was analyzed using an enzyme immunoassay technique.

Results:
65%, 40%, and 78% were exposed to B. thuringiensis, V. lecanii and T. harzenianum, respectively, while 6, 3 and 3% were handling the products. IgE against B. thuringiensis was seen in 53% of the samples and with prevalence rate ratios among exposed increasing from 1.20 (CI95%:1.01-1.42) to 1.43 (CI95%:1.09-1.87) over the 3-year period. There was no relation between exposure to any MBCA and neither prevalence nor incidence of respiratory symptoms and there was no effect on lung function or bronchial responsiveness.

Conclusions:
Use of B. thuringiensis in greenhouses may give rise to sensitization while no effect on the occurrence of respiratory symptoms or lung function was observed. The persons had a relatively long exposure. Therefore, a healthy worker effect may have influenced the results.