Prevalence of the sick building syndrome symptoms in office workers before and six months and three years after being exposed to a building with an improved ventilation system.

Aimed to find out if a decrease in sick building syndrome symptoms as the result of an improved ventilation system was still in force after three years. The buildings, both old and new, had sealed windows with mechanical ventilation, air conditioning, and humidification. The prevalence of most symptoms had originally decreased by 40% to 50%. The case was similar after three years.