Table 3.

School building characteristics and prevalence of SBS symptoms (N = 12)

Schools	Number of students	Building age (year)	Construction	Floor material	Ventilation type	Window panes	Heating energy	Humidity control	Mucosal symptoms	Skin symptoms	General symptoms
1	633	1	Ferroconcrete	Wood	Mechanical, exhaust	Paired glass	Natural gas	No	35 (6.7)	11 (2.1)	1 (0.2)
2	296	30	Ferroconcrete	PVC tiles	Natural	Single-glass, double-paned	Kerosene	No	11 (5.5)	4 (2.0)	1 (0.5)
3	906	35	Ferroconcrete	PVC tiles	Natural	Single-glass, double-paned	Natural gas	No	51 (8.7)	7 (1.2)	2 (0.3)
4	329	36	Ferroconcrete	PVC tiles	Natural	Single-glass, double-paned	Kerosene	No	17 (8.8)	2 (1.0)	2 (1.0))
5	494	46	Ferroconcrete	PVC tiles	Natural	Single-glass, double-paned	Natural gas	No	19 (7.6)	8 (3.2)	5 (2.0)
6	529	27	Ferroconcrete	PVC tiles	Mechanical, exhaust	Single-glass, double-paned	Kerosene	Yes	29 (7.7)	7 (1.8)	4 (1.1)
7	552	26	Ferroconcrete	PVC tiles	Natural	Single-glass, double-paned	Natural gas	No	23 (5.4)	9 (2.1)	7 (1.6)
8	113	30	Ferroconcrete	Wood	Mechanical, exhaust	Single-glass, double-paned	Electricity	No	3 (3.1)	0 (0.0)	0 (0.0)
9	677	18	Ferroconcrete	PVC tiles	Natural	Single-glass, double-paned	Natural gas	No	36 (7.2)	9 (1.8)	5 (1.0)
10	645	24	Ferroconcrete	PVC tiles	Natural	Single-glass, double-paned	Electricity	No	34 (7.3)	13 (2.7)	3 (0.6)
11	742	< 1	Prefabricate	Wood	Natural	Paired glass	Natural gas	No	11 (3.6)	10 (2.0)	4 (0.8)
12	477	14	Ferroconcrete	PVC tiles	Natural	Single-glass, double-paned	Natural gas	No	11 (6.9)	7 (2.3)	1 (0.3)

Based on chi-square test, no significant difference was observed in the prevalence of all SBS symptoms among schools