Trends in the prevalence of Beijing children s asthma and allergies over 20 years Fang Qu 1, Yinping Zhang 1*, Jan Sundell 1 1 Institute of Built Environment, Department of Building Science, Tsinghua University, Beijing 10084, China * Corresponding email: zhangyp@tsinghua.edu.cn SUMMARY Data from a new cross-sectional study is compared with earlier data from 1990 to 2008 for the prevalence of asthma and allergies among children in Beijing. In 2011, a questionnaire survey was carried out in randomly selected kindergartens. 5880 children aged 1 to 8 years were investigated. The prevalence of children s asthma increased from 0.78% in 1990 to 6.02% in 2011. The prevalence of bronchial asthma was higher among boys than girls. The boys to girls prevalence ratio decreased with age. KEYWORDS asthma, epidemiology, allergies, surveys 1 INTRODUCTION Asthma is the most common chronic disease of childhood (Pendersen et al. 2011), affecting, for example, nearly 6.5 million children in the United States (US EPA, 2007). Asthma represents a challenge to public health systems and health care providers throughout the world (Malveaux, 2009; NCHS, 2002). The prevalence of asthma and allergies has been increasing in developed countries over recent decades, especially in children (Beasley et al. 1998; ISAAC, 1998; Kay, 2001; Peat et al. 1995). The prevalence of asthma has also increased in developing countries (Asher et al. 2006), including China and India, although the prevalence in the Chinese mainland has been lower than that of other countries (Lai et al. 1996). Although Beijing, the capital of China, is the nation's political and cultural center, there is little information on trends in Beijing s childhood asthma in the past two decades. Surveys in 1990 (NCGCA, 1993), 2000 (Ma et al. 2002) and 2008 (Zhao et al. 2010) found asthma rates of 0.78%, 2.05% and 3.15%, respectively. In this investigation, we conducted a cross-sectional questionnaire survey regarding housing and health among children aged 1-8 in Beijing in 2011. We compared asthma prevalence data from the previous studies to assess the increase in childhood asthma and allergies among children aged 1-8 in Beijing over 20 years of cross-sectional studies. It is anticipated that this study will be useful to public health policymakers. 2 METHODS The epidemiological cross-sectional questionnaire survey was similar to the questionnaire used in the DBH studies performed in Sweden, Bulgaria, and Texas (Larsson et al. 2009; Bornehag et al. 2005; Naydenov et al. 2005), but with additional questions adapted to Chinese housing characteristics. All preschool children in randomly selected kindergartens were invited to participate in the study. Kindergarten teachers distributed the questionnaires to parents in the period Jan-May 2011. The response rate to written questionnaires was about 65%. Asthma was defined as a yes response by children s parents or guardian to the question Has your child ever been diagnosed with asthma by a doctor?
The χ 2 test was used to compare asthma rates in different groups of children. P values of less than 0.05 were considered to be statistically significant. 3 RESULTS Table 1 compares the present dataset to previous datasets. Prevalence rates (%) of asthma with gender distribution for the 5880 participating children aged 1-8 years are summarized in Table 1. In all these investigations, the number of boys surveyed was slightly greater than that of girls. Asthma rates have increased in Beijing. The prevalence of asthma in 1990, 2000, 2008 and 2011 was 0.78%, 2.95%, 3.15%, 6.02%, respectively. Worldwide, asthma is more prevalent in boys than girls (Anthracopoulos et al. 2011). Similarly, a marked gender difference (P < 0.001) was found in Beijing children from 2000 to 2011. Asthma rates for boys and girls were 2.80% and 1.22% in 2000, and 4.09% and 2.05% in 2008. Compared with 2000 and 2008, the rates for boys and girls have increased to 7.55% and 4.34% in 2011. However, the ratio of asthma rates in boys to that in girls has declined somewhat. In 2000, 2008 and 2011, the ratios were 2.30:1, 2.00:1 and 1.74:1 respectively. Decreasing gender ratios have similarly been found in some studies (Devenny et al. 2004; Venn et al. 1998) but increasing ratios have been found in others (Anthracopoulos et al. 2007; Selnes et al., 2005). Table 2 shows that there have been significant increases in the prevalence of asthma in different age groups in Beijing during 1990 to 2011. Other allergic symptoms surveyed were wheeze, dry cough at night and eczema. The prevalence of such symptoms was assessed by an answer of yes to the following questions: Has your child had wheezing or whistling in the chest in the last 12 months? In the last 12 months, has your child had a dry cough at night for more than two weeks, apart from a cough associated with a cold or chest infection? Has your child ever had itchy skin that lasted more than 6 months? Table 3 shows that the prevalence of allergies in Beijing between 2008 and 2011 has increased. 4 DISCUSSION In the past twenty years, the prevalence of Beijing childhood asthma has been rising steadily. The prevalence of children s asthma in 2011 was almost seven times greater than in 1990. The lowest asthma rates are for 1 to 2 year-old children in Table 2. The rates do not increase greatly with increasing age for the 1990 or 2000 children. However, rates increase with age in the 2008 children, and even more dramatically in the 2011 children. Wheeze was the most common clinical manifestation, followed by persistent cough and recurrent respiratory infections (Bai et al. 2010). Table 3 shows the prevalence of wheeze, dry cough and eczema to be increasing trends. The cross-sectional surveys of 1990, 2000 and 2008 were conducted by a national cooperative group on childhood asthma in China, using the International Study of Asthma and Allergies in Childhood (ISAAC) group s questionnaire (Pearce et al. 1993). Our core questions were adopted from the ISAAC protocol, but also added questions to assess home environmental factors that might impact asthma and allergy rates. Thus, the present study establishes a baseline for studying the impact of home environmental factors on asthma and allergies. 5 CONCLUSIONS Asthma and allergies are the most frequent chronic childhood diseases. To analyze trends in children s asthma prevalence in Beijing, we compared the results of 4 surveys. These epidemiologic studies provide evidence of increasing rates of asthma and allergies in Beijing over the past two decades. The prevalence of Beijing children s asthma in the 1990, 2000, 2008 and 2011 surveys were 0.78%, 2.05%, 3.15% and 6.02%,respectively (P < 0.001).
Table 1 Prevalence (%) of Asthma in Children in Beijing from 1990 to 2011 Year 1990 2000 2008 2011 P value Number of children 10,947 10,163 10,372 5,880 Study Period 1990 Jun-Oct 2000 Oct 2008-Mar 2009 Jan-May 2011 Gender Boys, n (%) / 5,252 (51.7%) 5,455 (52.6%) 3,061 (52.1%) Girls, n (%) / 4,911 (48.3%) 4,917 (47.4%) 2,785 (47.4%) Ratio (B:G) / 1.07 1.11 1.1 Children with asthma, n (%) 86 (0.78) 208 (2.05) 324 (3.15) 354 (6.02) < 0.001 Boys with asthma / 147 (2.80) 223 (4.09) 231 (7.55) < 0.001 Girls with asthma / 61 (1.22) 101 (2.05) 121 (4.34) < 0.001 Ratio of Prevalence (Boys:Girls) / 2.30 2.00 1.74 Refs NCGCA, 1993 Ma et al. 2002 Zhao et al. 2010 & Bai et al. 2010. Present study 2011
Table 2 Relationship between Age and Prevalence (%) of Children's Asthma in Beijing during 1990 to 2011 Year Age yrs 1990 2000 2008 2011 1 / 1.39 0.55 / 2 0.80 1.24 1.76 1.61 3 1.21 1.86 4.47 4.83 4 1.61 2.18 4.33 6.04 5 1.37 2.63 5.00 6.40 6 1.26 1.51 4.86 7.44 7 1.00 2.55 3.93 6.49 8 0.42 3.14 3.70 / Refs Ma et al 2002 Ma et al 2002 Zhao et al 2010 Present study 2011 Table 3 Prevalence of Allergies in Beijing from 2008 to 2011 Year Symptoms 2008 2011 Chi-square Test n % n % P value Wheeze in last 12 months 575 5.54 858 14.59 < 0.001 Dry cough at night in last 12 months 903 8.71 1,118 19.01 < 0.001 Eczema > 6 months in duration 181 1.75 1,626 27.65 < 0.001 Refs Zhao et al 2010 Present study 2011 Compared with 1990 s data, the prevalence of children s asthma in 2011 was nearly seven times greater. The prevalence of wheeze, dry cough at night and eczema has also increased significantly. The prevalence of asthma and wheeze in boys has been much higher than that in girls. However, the boys to girls ratio in 2011 was less than that of 2008. In conclusion, the cross-sectional surveys suggested that the prevalence of childhood asthma and allergies in 2011 was significantly higher than in previous surveys in Beijing dating to 1990. Further investigations are necessary to determine the possible environmental factors which may have increased the prevalence of asthma and allergies in Chinese children in Beijing. ACKNOWLEDGEMENT We are grateful to the kindergarten teachers and the almost 6,000 children and their parents, who generously participated in the surveys. 6 REFERENCES Anthracopoulos M.B., Liolios E., Panagiotakos D.B., Triantou K., Priftis K.N. 2007. Prevalence of asthma among schoolchildren in Patras, Greece: four questionnaire surveys during 1978-2003. Archives of Disease in Childhood, 92(3), 209-212. Anthracopoulos M.B., Pandiora A., Fouzas S., Panagiotopoulou E., Liolios E., Priftis K.N. 2011. Sex-specific trends in prevalence of childhood asthma over 30 years in Patras, Greece. Acta Pædiatrica, 100(7), 1000-1005. Asher M.I., Montefort S., Bjorksten B., Lai C.K., Strachan D.P., Weiland S.K., et al. 2006. Worldwide time trends in the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and eczema in childhood: ISAAC phases one and three repeat multicountry cross-sectional surveys. Lancet, 368(9537), 733-743.
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