Table 1 Demographics of the study population of boys (N = 15,673) and girls (N = 15,376) in seven cities of Northeast China

Asthma and asthma related symptoms

Doctor-diagnosed asthma

1179 (7.5)

856 (5.6)^*

2035 (6.6)

 Current asthma

410 (2.6)

288 (1.9)^*

698 (2.3)

 Current wheeze

1082 (6.9)

883 (5.7)^*

1965 (6.3)

 Persistent cough

1538 (9.8)

1439 (9.4)

2977 (9.6)

 Persistent phlegm

761 (4.9)

660 (4.3)^*

1421 (4.6)

Allergic predisposition

 Family history of allergic

1124 (7.2)

1153 (7.5)

2277 (7.3)

 Family history of asthma

1227 (7.8)

1185 (7.7)

2412 (7.8)

 Family history of allergic/asthma

2134 (13.6)

2106 (13.7)

4240 (13.7)

 Personal allergic history

3393 (21.7)

3006 (19.6)^*

6399 (20.6)

 Personal hay fever history

2101 (13.4)

1368 (8.9)^*

3469 (11.2)

Environmental factors exposures

 Exposure to pets during pregnancy

627 (4.0)

523 (3.4)^*

1150 (3.7)

 Exposure to pets in the first years of life

878 (5.6)

968 (6.3)

1846 (6.0)

 Avoidance to pet exposure

141 (0.9)

108 (0.7)

249 (0.8)

Current exposure to pets

 Yes

2339 (14.9)

2569(16.7)^*

4908(15.8)

Number of pets

 1

1886 (12.0)

2027 (13.2)

3913 (12.6)

 ≥2

453 (2.9)

542 (3.5)

995 (3.2)

 Dogs

878 (5.6)

999 (6.5)^*

1877 (6.0)

 Cats

736 (4.7)

830 (5.4)^*

1566 (5.0)

 Birds

455 (2.9)

507 (3.3)

962 (3.1)

 Farm animals

282 (1.8)

384 (2.5)^*

666 (2.1)

 Other pets

533 (3.4)

523 (3.4)

1056 (3.4)

ETS exposure^†

7779 (49.6)

7537 (49.0)

15316 (49.3)

House decoration in recent two years

5342 (34.1)

5223 (34.0)

10565 (34.0)

Breast feeding

13517 (86.2)

13464 (87.6)^*

26981 (86.9)

Number of room <3

8484 (54.1)

8183 (53.2)

16667 (53.7)

Home coal use

1055 (6.7)

1016 (6.6)^*

2071 (6.7)

Commercial health insurance

4059 (25.9)

2260 (14.7)^*

6319 (20.4)

Education level of parents < high school

4361 (27.8)

4123 (26.8)^*

8484 (27.3)