Table 1 Sociodemographic characteristics of the respondents

Gender

 Male

19,405

51.6

 Female

18,169

48.4

Age, years (Mean ± SD)

13.53 ± 2.53

 9~

3675

9.8

 10~

4195

11.2

 11~

4332

11.5

 12~

4349

11.6

 13~

4286

11.4

 14~

4279

11.4

 15~

4170

11.1

 16~

4443

11.8

 17~

3845

10.2

City

 Nanjing

16,572

44.1

 Huai’an

10,317

27.5

 Changzhou

10,685

28.4

Board at school

 Yes

14,408

38.3

 No

23,166

61.7

BMI (kg/m²) (Mean ± SD)

20.01 ± 3.94

 Non overweight or obese ^a

31,307

83.3

 Overweight ^a

4789

12.7

 Obese ^a

1478

3.9

Recent acute symptoms

 Feverish

  No

36,259

96.5

  Yes

1315

3.5

 Coughs

  No

14,087

37.5

  Yes

23,487

62.5

 Sore throat

  No

28,244

75.2

  Yes

9330

24.8

 Diarrhea

  No

28,291

75.3

  Yes

9283

24.7