2. Materials and methods
2.1. Study population
Changchun and Yanji city of Jilin province (China) are selected as the research cities. Two primary schools are randomly selected from each city. The study population consisted of students from grade third to fifth enrolled in the four schools in October 2016, at least 200 students are selected for each grade, and the sampling method is cluster random sampling. We assess the impact of environmental factors on respiratory health in children (n =2419).
2.2. Exposure assessment
The environmental impact factors were assessed through the parental Questionnaire. Whether there is a stinky ditch, garbage station, heating company or noise in 100 meters around home; The distance from home to main traffic road; Whether decorated house within three years; Whether bought furniture within a year; Window opening in winter; Passive smoking (smoke inhaled every day for more than 15 minutes); Main heating mode; Main fuel for cooking; The presence or absence of pets; The use of fume exhauster, insecticide, anophelifuge, moth repellant, air freshener, disinfectant, and air cleaner were queried.
2.3. Health outcome assessment
Children’s health outcomes included recurrent respiratory tract infection, pneumonia, asthma, tracheitis/ bronchitis and rhinallergosis, also ascertained by the parental questionnaire. All diseases are clinically confirmed and have a clear diagnosis report. A subset of the study population underwent analysis of pulmonary function at designated hospital or medical examination center after children’s weight and standing height were obtained(n = 627). The contents of pulmonary function analysis included forced vital capacity(FVC), forced expiratory volume in 1 second (FEV1), peak expiratory flow velocity (PEF), forced expiratory flow at 25%FVC (V25) and forced expiratory flow at 75%FVC(V75).
2.4. Ethical Standards
The Ethics Committee of Jilin Provincial Center for Disease Control and Prevention approved this study. Written informed consent was obtained from each participant signed by their parents.
2.5. Quality Control
All investigators were trained before the investigation. In the survey, a questionnaire was set up to verify the questionable questionnaire on the day. If necessary, a reinvestigation was needed to correct the mistakes and leak out the vacancy. The data were parallel double entered and corrected according to the consistency test report. The measurement instruments used were calibrated according to the same standard.
2.6. Statistical analysis
The database was established by EPIDATA 3.1, and statistical analysis was carried out by SPSS 17.0 statistical software. The categorical variables were described as numbers and frequency and the continuous variables were described as \(\overset{\overline{}}{x}\ \)± s (mean ± standard deviation). The χ2 test and t-test and were adopted on comparison between two groups. The least significant difference (LSD) procedure and the One-Way ANOVA were used to compare the means of three groups. To Analyze the environmental impact factors of respiratory diseases, we use multivariate logistics regression analysis. A P -value < 0.05 (two-tailed) was considered to be statistically significant.