Table 1.

Characteristics of adolescent contacts of the index TB cases and of the controls.

Exposure variables	Control class (N = 6130)		Index TB class (N = 6263)		P-value chi-square test
	n	%	N	%
School type
Middle school	2233	36.43	2333	37.25	0.352
High school	3897	63.57	3930	62.75
School location
Urban district	1881	30.69	1891	30.19	0.33
County	4249	69.31	4372	69.81
School residential
Ambulatory	475	7.7	607	9.69	<0.001
Boarding	5655	92.3	5656	90.31
Gender
Female	3142	51.26	3153	50.34	0.318
Male	2988	48.74	3110	49.66
Age, years
≤15	1792	29.23	1847	29.49	0.768
>15	4338	70.77	4416	70.51
Ethnicity
Others	2494	40.69	2456	39.21	0.098
Han	3636	59.31	3807	60.79
Birth place
City	763	12.45	991	15.82	<0.001
Rural	5367	87.55	5272	84.18
BCG scar
Present	4399	71.76	4403	70.3	0.076
Absent	1731	28.24	1860	29.7