Study sites
Jinshan District is in the southwest suburb of Shanghai Municipality, with a population of 520,404, nearly half of which are urban population in 2016. The area is 44 km long from east to west and 26 km wide from north to south. It includes 11 townships with a total area of 613 km2. Jinshan District is the only districts in Shanghai where the economy is dominated primarily by chemical industries and agriculture. Based on the location of the chemical industrial zones (Shanghai chemical industry zone in CJ, Shanghai petrochemical industry zone in SH, and Jinshan second industrial zone in JSW) in Jinshan, the 11 townships were divided into CIA and nonchemical industrial areas (non-CIA) (Figure 1a). CIA include three townships, CJ, JSW, and SH. Non-CIA include eight townships: FJ, LvX, LX, SY, ZY, ZJ, TL, and JSGYQ.
Subjects
General surveys including questionnaires and measurements were conducted on the first-grade school children enrolled in 2015 during the fall semester in all the 28 primary schools within the 11 townships in Jinshan District, Shanghai. Measurements were completed between May and June 2016, while all the questionnaire surveys were finished in September 2016.
Questionnaires
The questionnaires consisted of the following three main parts: (1) general demographic information of first-grade school children, (2) health status of first-graders, and (3) children’s environmental exposures including indoor pollution and surrounding potential pollution sources within 300 m of the residence.
The basic demographic information investigated included school, class, townships, sex, date of birth, birth weight, birth outcome, parents’ occupations, and parents’ educational levels.
The health problems included diseases diagnosed by physicians in the previous year and acute symptoms experienced at least once in the last month. Diseases were defined as follows: (1) respiratory diseases (RD): recurrent respiratory infection, pneumonia, asthma, tracheitis, allergic rhinitis, or other respiratory diseases; (2) digestive diseases: gastritis, peptic ulcer, acute diarrhea, gastroesophageal reflux, or other digestive diseases; and (3) skin diseases: pruritus, eczema, urticaria, conjunctivitis, trachoma, or other skin diseases. Acute symptoms were defined as follows: (1) respiratory symptoms: throat irritation, nasal obstruction, discomfort, cough, expectoration, shortness of breath, or other respiratory symptoms; (2) eye symptoms: eye irritation or other eye symptoms; (3) neurological symptoms: headache, dizziness, weakness, insomnia, memory loss, inattention, abnormal sensation, limb pain, or other neurological symptoms; (4) digestive symptoms: anorexia, nausea and vomiting, stomachache, or other digestive symptoms; and (5) skin symptoms: itch, eczema, alopecia, or other skin symptoms.
Indoor pollution included household smoking, pollutants from indoor decorations, or pollutants after purchasing furniture the previous year, use of air eliminators, and use of heaters during winter. Surrounding sources included traffic trunks, barbecue restaurants, and nonchemical enterprises. The investigators explained the questionnaires consistently to all participants, and the participating students filled out the questionnaire with the help of their parents.
Measurements
Measurements included physical examinations and hematological tests. The subjects were asked to take off their shoes and wear light clothes before measurement, and an ultrasonic height and weight meter was used to measure these parameters. Fasting was also required before obtaining blood samples, and all the blood samples were collected and analyzed by physicians in clinical pathology-accredited laboratories. Complete blood count (CBC) parameters were examined (Table A2).
Data processing
Weight status was classified as underweight (≤13.4 kg/m2 for girls, ≤13.9 kg/m2 for boys), normal weight (13.5–17.1 kg/m2 for girls, 14.0–17.3 kg/m2 for boys), overweight (17.2–18.8 kg/m2 for girls, 17.4–19.1 kg/m2 for boys), and obesity (≥18.9 kg/m2 for girls, ≥19.2 kg/m2 for boys) using body mass index (BMI) cutoff points, following the method of the Working Group for Obesity in China (WGOC) for 7-year-old children [12]. Moreover, BMI was calculated.
To eliminate the strong correlation between parents’ educational background, we used a new variable, parents’ educational level (the higher educational level received by any parent), rather than separately analyzing the father and the mother’s educational level. Additionally, because few parents have completed junior high school or below, junior high school or below and senior high school were combined into one variable to avoid extreme values and guarantee the stability of models.
Statistical analysis
We first summarized the demographic statistics and CBC parameters of first-graders. Subsequently, we used t-test for continuous variables such as height and χ2 test for categorical variables such as sex to analyze the differences between non-CIA and CIA. Then, we assessed the geographical distribution and detected high-risk clusters of prevalence of diseases and birth status in first-graders based on school locations using the Kulldorff method of spatial scan statistic based on a discrete Poisson model with maximum spatial cluster size of 30% of population at risk using SaTScan (version 9.6, Martin Kulldorff and Information Management Services Inc). Mapping was performed in QGIS Desktop (version 3.0.3, https://www.qgis.org/).
Finally, the logistic regression model was used to measure the differences in the prevalence of diseases and acute symptoms between CIA and non-CIA. We included all the variables with value p>0.1 under the univariate analysis into the multivariate logistic regression model, and the “backward elimination” method was used to screen the potential risk variables. Potential confounding variables were considered during the modeling process including sex, parents’ educational levels and occupations, indoor pollutant exposures, and outdoor environmental exposures within 300 m of the residence. Adjusted odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were calculated. All statistical analyses were performed using R 3.5.3 (R Project for Statistical Computing, http://cran.r-project.org).