There are few incidence studies on sick building syndrome (SBS). We studied two-year change of SBS in Chinese pupils in relation to parental asthma/allergy (heredity), own atopy, classroom temperature, relative humidity (RH), absolute humidity (AH), crowdedness, CO2, NO2, and SO2. A total of 1993 participated at baseline, and 1143 stayed in the same classrooms after two years. The prevalence of mucosal and general symptoms was 33% and 28% at baseline and increased during follow-up (P<0.001). Twenty-seven percent reported at least one symptom improved when away from school. Heredity and own atopy were predictors of SBS at baseline and incidence of SBS. At baseline, SO2 was associated with general symptoms (OR = 1.10 per 100 μg/m3), mucosal symptoms (OR = 1.12 per 100 μg/m3), and skin symptoms (OR = 1.16 per 100 μg/m3). NO2 was associated with mucosal symptoms (OR = 1.13 per 10 μg/m3), and symptoms improved when away from school (OR = 1.13 per 10 μg/m3). Temperature, RH, AH, and CO2 were negatively associated with prevalence of SBS. Incidence or remission of SBS was not related to any exposure, except a negative association between SO2 and new skin symptoms. In conclusion, heredity and atopy are related to incidence and prevalence of SBS, but the role of the measured exposures for SBS is more unclear.Practical Implications
We found high levels of CO2 indicating inadequate ventilation and high levels of SO2 and NO2, both indoors and outdoors. All schools had natural ventilation, only. Relying on window opening as a tool for ventilation in China is difficult because increased ventilation will decrease the level of CO2 but increase the level of NO2 and SO2 indoors. Prevalence studies of sick building syndrome (SBS) might not be conclusive for causal relationships, and more longitudinal studies on SBS are needed both in China and other parts of the world. The concept of mechanical ventilation and air filtration should be introduced in the schools, and when planning new schools, locations close to heavily trafficked roads should be avoided.