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

Objective--The prevalence of symptoms associated with the sick building syndrome (SBS) has recently been shown to decrease by 40% to 50% among office workers six months after they were exposed to a building with an improved ventilation system. The objective of the present study was to find whether the decrease in the prevalence of symptoms was maintained three years later. Methods--Workers from the same organisation occupied five buildings in 1991 and moved during that year to a single building with an improved ventilation system. All buildings had sealed windows with mechanical ventilation, air conditioning, and humidification. Workers completed a self administered questionnaire during normal working hours in February 1991 before moving, in February 1992 six months after moving, and in February 1995, three years after moving. The questionnaire encompassed symptoms of the eyes, nose and throat, respiratory system, skin, fatigue, and headache, as well as difficulty concentrating, personal, psychosocial, and workstation factors. During normal office hours of the same weeks, environmental variables were measured. Results--The study population comprised 1390 workers in 1991, 1371 in 1993, and 1359 in 1995, which represents 80% of the population eligible each year. The prevalence of most symptoms decreased by 40% to 50% in 1992 compared with 1991. This was similar in 1995. These findings were significant and remained generally similar after controlling for personal, psychosocial, and work related factors. Conclusion--In this study, the decrease of 40% to 50% in the prevalence of most symptoms investigated six months after workers were exposed to a new building with an improved ventilation system was maintained three years later. The results of the present follow up study provide further support for a real effect of exposure to a new building with an improved ventilation system on the prevalence of symptoms associated with the SBS.