| Bronchial asthma (asthma) is a common chronic inflammatory airway disease, mainly caused by T lymphocytes, mast cells, eosinophils and so on, moreover, lead to airway hyperresponsiveness and reversible airway obstruction. Asthma symptoms during night or early morning include recurrent grasp, dyspnea, stuff chest, cough, etc. The asthma is common and frequently encountered in pediatrics, and can seriously affect people of all the ages. It is estimated by WHO that there are about 300 million asthma patients in the worldwide and about 15 million asthma patients lost their labor every year. Mealwhile, there are 20 million asthma patients in China now. With the change of living environment and life style, the morbidity of asthma is increasing in past 50 years,which brings heavy burden of the social economic and enormous expense to national economy,and also become one of the serious public health problems. Therefore, a positive programme of asthma prevention is critical worldwide problem.The mechanism of asthma is complicated and largely attribute to genetic factors, allergens and environmental factors. Knowing the prevalence and related factors of asthma, can effectively make prevention strategy against asham for our country, so as to reduce the disease burden.To investigate the prevalence of asthma among children aged under 14 years old in China and related factors of asthma(air pollutants, personal behavior and life style, biological factors and several common gene polymorphisms that were associated with immunity), a series of Meta-analysis and systematic reviews were conducted in this study,which can overall evaluate the general aspect of prevalence of pediatric asthma, and further discusse related factors of asthma, and provide basis for prevention strategy against asthma in future research.PubMed, EMBASE, Science databases and several Chinese databases were systematic searched, to identify original articles regarding of the prevalence of asthma and the association study between asthma and air pollutants, personal behavior and life style, biological factors and several common gene polymorphisms that were associated with immunity. The retrieval language is Chinese and English. Publication time from 1990 to 2015. The inclusion criteria:(1) The content of the papers includes the prevalence of the pediatric asthma and related factors of asthma; (2) Observational study; (3) required data is valid; (4) article published; (5) Genotype distribution in consistent with Hardy-Weinberg equilibrium(HWE) in general population, the exclusion criteria:(1)The subjects are animals; (2)Reviews; (3)The research population cannot conform to the study purpose; (4)The literature cannot provide the required data directly or indirectly in the present study; (5)Experimental studies. The quality of literature is evaluated according to the proposed guidelines from Stroup. Analyses were performed using the software Stata version 10.0 and Review Manager 5.2. Heterogeneity was explored using the Q-statistic and I2 test. Two models of meta-analysis(the fixed-effects model (I2<50%) and the random-effects model(I2>50%))were applied for dichotomous outcomes according to the results of heterogeneity tests among individual studies:The pool ORs(Odds ratios) with their 95% CIs(confidential intervals) were used as effective targets.1. The studies showed that the prevalence rate of asthma were 2.4% (95% CI: 1.7%-3.2%), and boys in 2.6% (95% CI:1.9%-3.5%), girls in 1.7% (95% CI: 1.2%-2.4%).2. The association study between asthma and air pollutants:(1)The formaldehyde concentration in air exposure was higher in asthma group than that in the control group, mean deviation was 0.88(95% CI:0.77-1.00). (2)Elevated PM2.5 concentration increase childhood asthma outpatient visit in the day and second day, pool OR (95%CI) values were 1.03 (1.02-1.05) and 1.07 (1.00-1.14), respectively. However, elevated PM2.5 concentration has no influence on outpatient visit of children asthma in third and fifth day. (3)Elevated PM10 concentration increase childhood asthma outpatient visit frome the same day to fourth day, pool OR (95%CI) were 1.21 (1.16-1.27),1.05 (1.01-1.09), 1.073 (1.013-1.137) and 1.08 (1.05-1.12), respectively. (4)Elevated CO concentration has no influence on outpatient visit of children asthma on the same day, pool OR (95% CI) was 0.989 (0.968-1.009), but will make outpatient visit increasing in second, fourth and sixth day, pool OR (95% CI) was 1.039 (1.011-1.067),1.037 (1.003-1.072) and 1.052 (1.009-1.097), respectively. (5)Elevated air NO2 concentration will not affect the day children asthma outpatient visit number in the same day, pool OR (95%CI) was 1.016 (0.976-1.059), but will increase outpatient visit in the second and fourth day, pool OR (95%CI) was 1.027 (1.007-1.047) and 1.053 (1.017-1.091), respectively. (6)Elevated SO2 concentration does not affect children outpatient visit for asthma in the same, fourth and sixth day, pool OR (95%CI) was 1.032 (0.942-1.130),0.938 (0.876-1.004) and 0.975 (0.934-1.018), respectively, but will affect children outpatient visit in the second day, pool OR (95%CI) was 1.045 (1.07-1.073). (7)Elevated O3 concentration does not affect children outpatient visit number in the same, second and third day, pool OR (95%CI) were 1.022 (0.990-1.055),0.971 (0.919-1.027) and 1.02 (1.00-1.04), respectively, but the fourth days, pool OR (95%CI) was 1.043 (1.229-1.058).3. The association study between asthma and personal behavior and life style: There was a significant association between high BMI, passive smokingand asthma in children. The pool OR(95%CI) were 1.68 (1.46-1.94)and 1.51(1.35-1.69),. There was a significant difference for serum vitamin D level between bronchial asthma group and the control group (Z = 7.25, P<0.00001), the mean serum vitamin D level in asthma group (19.10ng/ml) was lower than in the control group,and 95% CI was (-24.26 to-13.94).4. The association study between asthma and biological factors:There was a significant association between HP and asthma (Z=2.04, P=0.04), OR(95%CI) was 0.84(0.71-0.99). Subgroup analysis revealed that there were statistically significant correlations between HP and asthma in non Asian population (Z=0.11, P=0.91), pooled OR(95%CI) was 1.03(0.59-1.82). There were statistically significant correlations between MP and asthma.(Z=21.67, P<0.00001), pooled OR(95%CI) was 3.69(3.28-4.15).The prevalence of asthma among Chinese children was higher, especially in coastal and developed cities, and the rate of asthma in boys was higher than in girls. Formaldehyde exposure was a risk factor for asthma in children. Air pollutants (PM2.5, PM10, CO, NO2, SO2 and O3) can predict outpatient visit number of children asthma. PM2.5 mainly affected children asthma acute attack. The effect of PM10 had a long time effect on asthma attack in children. CO, NO2, SO2 and O3 had a delayed effect on childhood asthma. There was a significant meaning to the prevention and control of asthmatic attack in children after understanding the relationship of time-effect between air pollutant concentration and children asthma attack. High body mass indexand passive smoking were risk factors for incidence of childhood asthma. Child obesity controland strengthening public smoking could guide the prevention of asthma in children. Serum vitamin D was protective factors for childhood asthma and might help reduce the incidence of asthma in children. HP was a protective effect for asthma among non-Asian populations. MP was a risk factor for asthma attacks. |
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