[Risks on asthma among city children in China:a nationwide case-control study].
OBJECTIVE
A case control study was designed to explore the risk factors of asthma for city children residing for more than half a year, in China.


METHODS
All physician-diagnosed asthma children enrolled in the 3(rd) nationwide survey (2010) in 43 typical cities of China were selected as the cases, and non-asthmatic children in the same survey were selected as control subjects if they were matched with the cases in age and sex. A revised questionnaire on the basis of ISAAC Phase Three Environmental Questionnaire was designed to investigate the risks of asthma among city children aged 0-14 years in China. Chi square analysis and generalized linear mixed models were performed to check the exposure difference between the cases and the controls.


RESULTS
43 out of the 44 city centers were qualified according to the results after reviewing both data from the survey and management. As a result, 26 950 subjects including 12 450 asthmatic children and 14 500 control subjects were enrolled in the case-control study. Except for the children of Han ethnicity, another 5 980 children (22.2%) of ethnic minorities and 31 children (0.1%)born in foreign countries were also included as the study subjects. After controlling for city centers as random effect, age, sex, race, problems related to allergy, family history of asthma or allergy, personal medication history of antibiotics, preterm delivery, under caesarean section, baby age for introducing protein-contained foods, environmental tobacco smoking, maternal occupation, indoor plantings, room decorations, dampness, and cooking fuel were proved to be risk factors of childhood asthma. Some differences were seen in the risks of asthma between new cases and current cases. The risk for exposure to indoor plants was different between new cases (OR = 2.09, 95%CI:1.30-3.36)and current cases (OR = 0.80, 95% CI:0.74-0.86). Risks on asthma were varied by age. Allergy, inflection, odor, and preterm delivery(OR = 1.72, 95%CI:1.42-2.08) appeared to be the key risks for asthma in children younger than 3 years. Apart from the risks, specifically for children younger than 3 years, the risks on asthma for children of 3 to 5 years would also include factors as: sex (OR = 1.18, 95%CI:1.03-1.35), low birth weight (OR = 1.69, 95%CI:1.17-2.44), and caesarean section (OR = 1.26, 95%CI:1.10-2.45). Apart from risks specifically for children younger than 6 years, age (OR = 0.97, 95%CI:0.95-0.99), race (OR = 1.61, 95%CI:1.26-2.06), and emigration (OR = 1.68, 95%CI:1.39-2.03) were proved to be associated with asthma for children aged 6-14 years.


CONCLUSIONS
Asthma risks for city children in China would include genetic factors, allergy, infection, and other environmental factors but called for further research in the country.
Institute for Environmental Health and Related Product Safety, Chinese Center for Disease Control and Prevention, Beijing 100050, China.
Qiang
Q
Wang
Institute for Environmental Health and Related Product Safety, Chinese Center for Disease Control and Prevention, Beijing 100050, China.
Chunyu
C
Xu
Institute for Environmental Health and Related Product Safety, Chinese Center for Disease Control and Prevention, Beijing 100050, China. Email: dongqunxu@126.com.
Dongqun
D
Xu
Center for Asthma Prevention and Education, Capital Institute of Pediatrics.
Chuanhe
C
Liu
Center for Asthma Prevention and Education, Capital Institute of Pediatrics. Email: chenyuzhi@gmail.com.
Yuzhi
Y
Chen
D000293:Adolescent; D001249:Asthma / Q000453:epidemiology*; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D002681:China / Q000453:epidemiology; D002947:Cities; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014505:Urban Population