The South Karelia Air Pollution Study: changes in respiratory health in relation to emission reduction of malodorous sulfur compounds from pulp mills.

The authors assessed the health effects of emission reduction of malodorous sulfur compounds in a prospective cohort study with a controlled natural experiment. A total of 810 subjects (83%) participated in the follow up: 316 from the severely polluted, 306 from the moderately polluted, and 188 from the nonpolluted communities. In the severely polluted community, the annual ambient air concentration of total reduced sulfur compounds decreased from 11 microg/m3 to 6 microg/m3. Compared with the nonpolluted community, the relative decrease in acute respiratory infections, adjusted for a change in smoking habits, was 0.53 episodes/person-year (95% confidence interval = 0.22, 0.83) in the severely polluted community and 0.36 episodes/person-year (95% confidence interval = 0.06, 0.66) in the moderately polluted community. In addition, the frequency of nasal symptoms (p = .004) and cough (p = .037) decreased significantly. The results are consistent with the hypothesis that exposure to malodorous sulfur compounds increases the risk of acute respiratory infections and symptoms of the respiratory tract.