Residential characteristics and household risk factors and respiratory diseases in Chinese women: The Seven Northeast Cities (SNEC) Study

Science of the Total Environment 463–464 (2013) 389–394

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Residential characteristics and household risk factors and respiratory diseases in Chinese women: The Seven Northeast Cities (SNEC) Study Guang-Hui Dong a,b, Zhengmin (Min) Qian c,⁎, Jing Wang d, Edwin Trevathan c, Wenjun Ma e, Weiqing Chen f, Pamela K. Xaverius c, Skye Buckner-Petty c, Asheesh Ray c, Miao-Miao Liu a, Da Wang a, Wan-Hui Ren g, Brett Emo h, Jen-Jen Chang c a

Department of Biostatistics and Epidemiology, School of Public Health, China Medical University, Shenyang, Liaoning Province 110001, China Department of Occupational and Environmental Health, School of Public Health, China Medical University, Shenyang, Liaoning Province 110001, China c Department of Epidemiology, School of Public Health, Saint Louis University, Saint Louis, MO 63104, USA d Department of Biostatistics, School of Public Health, Saint Louis University, Saint Louis, MO 63104, USA e Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, Guangdong Province 510300, China f Department of Epidemiology, School of Public Health, Sun Yat-sen University, Guangzhou 510080, China g Department of Ambient Air Pollution Monitor, Shenyang Environmental Monitoring Center, Shenyang, Liaoning Province 110014, China h Department of Environmental and Occupational Health School of Public Health, Saint Louis University, Saint Louis, MO 63104, USA b

H I G H L I G H T S • • • •

Relatively few significant associations were observed. Pet ownership was associated with increased odds of asthma and chronic bronchitis. Home renovation was associated with increased odds of allergic rhinitis in women. Humidifier use was associated with increased odds of chronic bronchitis in women.

a r t i c l e

i n f o

Article history: Received 3 January 2013 Received in revised form 2 May 2013 Accepted 13 May 2013 Available online 29 June 2013 Editor: Xuexi Tie Keywords: Residential characteristics Indoor environmental risk factors Women Respiratory diseases China

a b s t r a c t Background: Few studies have assessed the impact of residential home characteristics and home environmental risk factors on respiratory diseases in Chinese women. Therefore, this study sought to determine the association between residential home features, domestic pets, home renovation and other indoor environmental risk factors with respiratory health outcomes of Chinese women. Methods: This cross-sectional study included a study sample of 30,780 Chinese women aged 23 to 49 from 25 districts of seven cities in Liaoning Province, Northeast China. Information on respiratory health, residential characteristics, and indoor air pollution sources was obtained by a standard questionnaire from the American Thoracic Society. Multivariable logistic regression was used to estimate prevalence odds ratios (POR) and 95% confidence interval (95%CI). Results: The odds of respiratory diseases were higher for those who lived near the main road, or near ambient air pollution sources. Pet-keeping was associated with increased odds of chronic bronchitis (POR = 1.40; 95%CI: 1.09–1.81) and doctor-diagnosed asthma (POR = 2.07; 95%CI: 1.18–3.64). Additionally, humidifier use was associated with increased odds of chronic bronchitis (POR = 1.44; 95%CI: 1.07–1.94). Home renovation in recent 2 years was associated with increased likelihood of allergic rhinitis (POR = 1.39; 95%CI 1.17–1.64). Conclusion: Home renovation and residential home environmental risk factors were associated with an increased likelihood of respiratory morbidity among Chinese women. © 2013 Elsevier B.V. All rights reserved.

1. Introduction

⁎ Corresponding author at: Department of Epidemiology, School of Public Health, Saint Louis University, Salus Center/Room 473, 3545 Lafayette Avenue, Saint Louis, MO 63104, USA. Tel.: +1 314 977 8158; fax: +1 314 977 3234. E-mail address: [email protected] (Z.(M.) Qian). 0048-9697/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scitotenv.2013.05.063

Chronic respiratory diseases, including asthma, bronchitis, emphysema, and chronic obstructive pulmonary disease (COPD), have been a major cause of death and disability across all age groups (Bousquet et al., 2007; Glasgow, 2008; Peabody et al., 2005; Yusuf, 2009). Despite a declining trend in respiratory diseases in many countries over the past

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few decades, in recent years developing countries have witnessed an increase in the prevalence of respiratory diseases (Anandan et al., 2010; Bjerg et al., 2011; Chkhaidze et al., 2009; de Marco et al., 2011; Laurendi et al., 2012). Contemporary research studies have indicated that indoor air pollution is a key environmental risk factor contributing to this burden of respiratory disease (Desalu et al., 2010; Ingale et al., 2011; Kurmi et al., 2010; Laurendi et al., 2012; Regalado et al., 2006; Rumchev et al., 2007). Numerous studies have documented an association between chronic airflow obstruction in adults in developing countries, including China, with exposure to indoor air pollution resulting from the combustion of unprocessed solid fuels, such as biomass and charcoal, used for cooking and heating (Perez-Padilla et al., 2010; Kurmi et al., 2012). However, the rapid change and development within China over the past decade have been marked by massive construction and modernization projects as well as increased individual wealth. This economic boom has fueled new construction of large apartment complexes in addition to an increased demand for home renovation. During renovation, Chinese home dwellers' potential exposure to indoor air pollution is elevated either from the demolition process or from the new materials (Dong et al., 2008, 2011a). Meanwhile, with the improvement of the standard of living in China, the levels of indoor pollution from coal smoke have decreased rapidly as more people move to new homes supplied with gas and/or electric power (Dong et al., 2011b). Nonetheless, exposures to domestic pets and tobacco smoke remain a potential source of indoor air pollutants for many Chinese residents. Few research have investigated the health effects of indoor air pollution related to various features of the residential home environment (e.g., pet ownership, history of home renovation, humidifier use, and proximity to the road, factory, smokestack) on respiratory symptoms or diseases in Chinese women. Women in China are often in charge of domestic duties such as cooking which increases their exposure to air pollutants more than men. Therefore, the objective of the present study was to identify associations between indoor air pollution and respiratory diseases in urban adult Chinese women. 2. Methods

was not correlated with disease prevalence. 869 mothers were excluded from the study, including 600 who had less than 3 years of residence and 269 who had missing and/or “Not applicable” responses. 2.2. Questionnaire survey A self-administered questionnaire collected information on the residential history, type of dwelling (flat, terraced, semi-detached or detached), details of renovations of dwelling within the past 2 years (if any), sources of heat and light, fuels for cooking, the location of kitchen, types of ventilators, women's respiratory illnesses and symptoms and other medical history, education levels and smoking status of each member of the household in April 2009. The questionnaire was adapted from the American Thoracic Society (ATS) questionnaire. After reviewing the questionnaire, parents/guardians were invited to a Parents' Night to learn detailed information about the survey, including the objectives of the study and instructions on filling out the questionnaire. Parents who wished to complete the questionnaire at home were asked to have their child return the completed questionnaire in an envelope to the teacher. A standardized protocol was strictly followed for data entry and data management across all study sites (Qian et al., 2000; Dong et al., 2013). The primary outcomes of interest are respiratory medical conditions. We focused on three types of respiratory diseases — asthma, chronic bronchitis, and allergic rhinitis. Asthma was defined by the question “Has a doctor ever diagnosed the mother with asthma?”); chronic bronchitis was defined by the question “Has a doctor ever diagnosed the mother with chronic bronchitis?”; and allergic rhinitis was defined by the question “Has a doctor ever diagnosed the mother with allergic rhinitis?”. Environmental tobacco smoke (ETS) exposure was defined by the answer “Yes” to the question “Does anyone who living in the same house smoke cigarettes daily in this home?” Home renovation refers to the following activities in a home within the past 2 years: installation of polyvinyl chloride (PVC) flooring, hardwood floor, wallpaper, latex paints or plastic wall materials, new furniture, or synthetic carpet; the application of oil-based paints, or others (window or door replacement, aluminum and iron grills; roofing; plumbing; or electrical work).

2.1. Site selection and subject recruitment 2.3. Statistical methods The study participants were 31,049 mothers of schoolchildren who had participated in a parallel cross-sectional study of the effects of outdoor and indoor air pollution on respiratory health among children (Dong et al., 2013). The mothers resided in seven cities of the northeast China, i.e. Shanyang, Dalian, Anshan, Fushun, Benxi, Liaoyang and Yingkou, and each was asked to fill out a questionnaire. The seven cities were chosen to ensure varying levels of environmental pollution, socio-economic conditions, and types of manufacturing industries. There were five districts in Shenyang, four districts in Dalian and Fushun, and three districts in Anshan, Benxi, Liaoyang and Yingkou (25 districts in total). An elementary school (n = 25) and two kindergartens (n = 50) were randomly selected from each district under the condition that the district was within 1 km of an environmental monitoring station. Children at these institutions were asked to give a questionnaire handout and attached endorsed consent form to their parents or guardians to complete. All procedures were approved and in compliance with the ethical standards of the responsible committee on human experimentation of the China Medical University as well as the principles outlined in the Helsinki Declaration. Consent forms were obtained from participants who completed and returned the questionnaire. There were a total of 35,527 children from 25 elementary schools and 50 kindergartens, of whom 31,649 had their mothers complete the questionnaire, yielding an overall response rate of 89.1%. The participation rate varied from 81.3% in Yingkou to 94.7% in Dalian and

Descriptive analysis was used to characterize the study sample. Data were tested for normality (using the Shapiro–Wilk W-test) and homogeneity (using Bartlett's test for unequal variances). In each group, the mean ± SD was calculated for continuous variables, and frequencies were calculated for categorical variables. Chi square test statistics were calculated to assess associations between categorical variables. The associations between indoor air pollution and respiratory diseases were estimated by logistic regression models. Prevalence odds ratios (POR) and their 95% confidence intervals (95%CI) were calculated for indoor air pollution exposure adjusted by covariables of age, sex, and study district. The data were analyzed by the GLIMMIX procedure using the SAS software (version 9.2; SAS Institute, Cary, N.C., USA) to account for the cluster structure of the data. All statistical tests were two-tailed, and p values less than 0.05 were considered statistically significant. 3. Results Among the 30,780 mothers with valid responses, the prevalence rates of asthma, bronchitis and allergic rhinitis were 0.71%, 1.20% and 1.97%, respectively (Table 1). Higher prevalence of respiratory disease was associated with a parental history of respiratory diseases, types of home, number of rooms in the house, with proximity to a main road or an industrial factory or smokestack.

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The prevalence rate of respiratory diseases by indoor environmental risk factors is provided in Table 2. Women exposed to ETS had significantly higher prevalence rates of asthma (0.90% vs. 0.53%), chronic bronchitis (1.48% vs. 0.93%), and allergic rhinitis (2.33% vs. 1.61%) than those who were not exposed to ETS. Women living in homes renovated recently had a lower prevalence of chronic bronchitis (1.13 vs 1.24) but a higher prevalence of allergic rhinitis (2.48% vs. 1.70%) than those living in non-renovated homes. Women who were exposed to pets had higher prevalence of asthma (0.93% vs. 0.67%) and chronic bronchitis (1.74% vs. 1.10%) than those who were not exposed to pets. The prevalence of asthma for women exposed to a single pet at home was higher than those who had no pet at home and the prevalence of chronic bronchitis seemed to increase with the number of pets. Women who were exposed to dogs had higher prevalence rates of asthma and chronic bronchitis than those who were not, and women who were exposed to cats had a higher prevalence of bronchitis than those who were not. Furthermore, indoor coal combustion, ventilator use, smoke from cooking, and mold/ mildew or cockroaches in the home in the past 12 months were associated with increased rates of respiratory morbidities, whereas the prevalence of chronic bronchitis was lower (1.06% vs. 1.40%) for women living in homes with windows left open in winter. All statistically significant associations are indicated in bold typeface in Table 3. After controlling for potential confounders, home renovation in the past 2 years was significantly associated with an increased odds of allergic rhinitis (POR = 1.39; 95%CI 1.17–1.64). Pet ownership was significantly associated with an increased likelihood of chronic bronchitis (POR = 1.40; 95%CI: 1.09–1.81). The category of “Others” in type of

Table 1 Distribution of respiratory diseases by house types, locations and demographics among Chinese women in Liaoning Province, Northeast China (n = 30,780).

Total City Shenyang Dalian Anshan Fushun Benxi Liaoyang Yingkou Education level bHigh school ≥High school Parental history of atopya No Yes Parental history of bronchitis No Yes House type Apartment Othersb Room number in home b3 ≥3 House near major road No Yes House near a factory No Yes House near a smokestack No Yes

N

Asthma N(%)

Chronic bronchitis N(%)

Allergic rhinitis N(%)

30,780

218(0.71)

369(1.20)

605(1.97)

8662 4901 4158 3254 2641 3174 3990

67(0.77) 35(0.71) 26(0.63) 27(0.83) 23(0.87) 19(0.60) 21(0.53)

80(0.92) 68(1.39) 49(1.18) 63(1.94) 39(1.48) 26(0.82) 44(1.10)

159(1.84) 110(2.24) 62(1.49) 63(1.94) 69(2.61) 52(1.64) 90(2.26)

8353 22,427

66(0.79) 152(0.68)

117(1.40) 252(1.12)⁎

134(1.60) 471(2.10)⁎

29,342 1438

168(0.58) 49(3.41)⁎

312(1.06) 57(3.96)⁎

482(1.64) 123(8.55)⁎

30,057 723

193(0.64) 25(3.46)⁎

319(1.06) 50(6.92)⁎

553(1.84) 52(7.19)⁎

27,926 2854

188(0.67) 30(1.05)⁎

326(1.17) 43(1.51)

563(2.02) 42(1.47)⁎

14,286 16,494

95(0.66) 123(0.75)

137(0.96) 232(1.41)⁎

312(2.18) 293(1.78)⁎

18,885 11,895

115(0.61) 103(0.87)⁎

191(1.01) 178(1.50)⁎

327(1.73) 278(2.34)⁎

28,233 2547

191(0.68) 27(1.06)⁎

330(1.17) 39(1.53)

552(1.96) 53(2.08)

25,798 4982

172(0.67) 46(0.92)⁎

292(1.13) 77(1.55)⁎

478(1.85) 127(2.55)⁎

⁎ p b 0.05. a Parental atopy was defined as a history of maternal or paternal asthma, allergic eczema, allergic conjunctivitis or allergic rhinitis. b Dormitory or any other unspecified house type.

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Table 2 Percentage of Chinese women who had respiratory diseases by indoor environmental factors in Liaoning Province, Northeast China (n = 30,780). N

Environmental tobacco smoke No Yes Home renovation in the past 2 years No Yes Household pets No Yes Number of pets 0 1 ≥2 Type of pets Cat Dog Birds Farm animals Others Window left open in winter No Yes Humidifier use No Yes Indoor coal combustion heating No Yes Ventilator use No Yes Smoke from cooking No Yes Mold/mildew in the past 12 months No Yes Cockroaches in the past 12 months No Yes a

Asthma N(%)

Chronic bronchitis N(%)

Allergic rhinitis N(%)

15,733 83(0.53) 147(0.93) 254(1.61) 15,047 135(0.90)a 222(1.48)a 351(2.33)a 20,300 137(0.67) 10,480 81(0.77)

251(1.24) 345(1.70) 118(1.13)a 260(2.48)a

25,952 173(0.67) 285(1.10) 511(1.97) 4828 45(0.93)a 84(1.74)a 94(1.95) 25,952 173(0.67) 285(1.10) 511(1.97) 65(1.69)a 69(1.79) 3849 37(0.96)a 979 8(0.82) 19(1.94)a 25(2.55) 1273 1632 837 563 1001

5(0.39) 18(1.10)a 6(0.72) 4(0.71) 14(1.40)a

26(2.04)a 31(1.90)a 16(1.91)a 8(1.42) 13(1.30)

27(2.12) 31(1.90) 12(1.43) 16(2.84) 18(1.80)

12,516 102(0.81) 18,264 116(0.64)

175(1.40) 252(2.01) 194(1.06)a 353(1.93)

26,209 182(0.69) 4571 36(0.79)

310(1.18) 59(1.29)

512(1.95) 93(2.03)

28,759 195(0.68) 327(1.14) 569(1.98) 2021 23(1.14)a 42(2.08)a 36(1.78) 5189 51(0.98) 88(1.70) 83(1.60) 25,591 167(0.65)a 281(1.10)a 522(2.04)a 29,885 210(0.70) 895 8(0.89)

349(1.17) 582(1.95) 20(2.23)a 23(2.57)

27,554 194(0.70) 3226 24(0.74)

312(1.13) 521(1.89) 57(1.77)a 84(2.60)a

17,115 93(0.54) 13,665 125(0.91)

168(0.98) 275(1.61) 201(1.47)a 330(2.41)a

Control b 0.05 compared to “No” or reference group.

pets was associated with an increased odds of asthma (OR = 2.07; 95%CI: 1.18–3.64), and cat exposure was associated with an increased odds of chronic bronchitis (OR = 1.70; 95%CI: 1.12–2.56). Residing in homes along a main road was associated with an increased likelihood of asthma (POR = 1.34; 95%CI: 1.02–1.76), chronic bronchitis (POR = 1.34; 95%CI: 1.09–1.66), and allergic rhinitis (POR = 1.24; 95%CI: 1.05–1.46). Humidifier use was associated with increased odds of chronic bronchitis (POR = 1.44; 95%CI: 1.07–1.94). In addition, exposure to cockroaches in the past 12 months and mold/water damage in the home were both associated with an increased likelihood of respiratory diseases. There was no significant association between the prevalence of respiratory diseases and ETS exposure, indoor coal combustion, ventilator use, and smoke from cooking. 4. Discussion In the present study, several indoor environmental factors were associated with increased prevalence of one or more of the studied respiratory illnesses in urban Chinese women. Specifically, we observed: (1) pet ownership, humidifier use, and presence of three or more rooms in the home were associated with increased prevalence of chronic bronchitis, (2) home renovation was associated with increased prevalence of allergic rhinitis, and (3) residing close to a main road, which reflects exposure to outdoor air pollution, and the presence of mold and

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Table 3 Adjusted PORs and their 95% confidence intervals for indoor environmental risk factors associated with respiratory diseases among Chinese women.a

House near major road House near factory House near chimney Three or more rooms in house Environmental tobacco smoke Home renovation within the past 2years Household pets Number of petsb 1 ≥2 Type of petsb Cat Dog Birds Farm animals Others Window left open in winter Humidifier use Coal combustion Ventilator use Smoke from cooking Mold or mildew presence in the past 12 months Cockroaches in the past 12 months

Asthma

Chronic bronchitis

Allergic rhinitis

1.34 1.44 1.24 1.04

1.34 0.74 1.19 1.37

1.24 0.74 1.29 0.85

(1.02, 1.76) (0.86, 2.42) (0.87, 1.79) (0.78, 1.39)

(1.09, 1.66) (0.48, 1.15) (0.89, 1.58) (1.09, 1.72)

(1.05, 1.46) (0.52, 1.05) (1.04, 1.60) (0.72, 1.02)

1.32 (0.96, 1.80)

1.22 (0.96, 1.56)

1.17 (0.97, 1.41)

1.23 (0.92, 1.64)

0.98 (0.78, 1.24) 1.39 (1.17, 1.64)

1.18 (0.84, 1.66) 1.40 (1.09, 1.81) 0.92 (0.73, 1.16) 1.25 (0.87, 1.81) 1.38 (1.05, 1.83) 0.88 (0.68, 1.14) 0.95 (0.46, 1.97) 1.48 (0.91, 2.41) 1.05 (0.69, 1.60) 0.51 1.24 0.96 0.74 2.07 0.83 1.27 1.14 0.79 0.93 0.70

(0.21, 1.25) (0.74, 2.08) (0.42, 2.19) (0.27, 2.04) (1.18, 3.64) (0.63, 1.11) (0.87, 1.86) (0.64, 2.05) (0.53, 1.16) (0.44, 1.93) (0.42, 1.17)

1.70 1.39 1.62 0.94 1.13 0.83 1.44 1.52 0.82 1.51 1.50

(1.12, 2.56) (0.93, 2.06) (0.97, 2.72) (0.45, 1.94) (0.64, 2.01) (0.67, 1.03) (1.07, 1.94) (0.98, 2.36) (0.61, 1.10) (0.93, 2.44) (1.05, 2.15)

0.98 0.93 0.66 1.20 0.82 0.92 1.01 1.07 1.08 1.05 1.37

(0.66, 1.46) (0.64, 1.36) (0.37, 1.18) (0.71, 2.03) (0.51, 1.33) (0.78, 1.10) (0.80, 1.28) (0.70, 1.64) (0.82, 1.41) (0.68, 1.64) (1.04, 1.81)

1.41 (1.04, 1.92) 1.25 (0.99, 1.59) 1.37 (1.14, 1.65)

a POR adjusted for parental history of atopy and bronchitis, education level, house type, and city of residence. b Reference category = no pet ownership.

cockroaches in the home, were also associated with respiratory diseases. ETS exposure was not associated with any respiratory disease of interest. It has been controversial as to whether or not pet ownership prevents specific allergic sensitization or reduces the risk of respiratory diseases. There has been little literature about the effect of pet ownership on adult respiratory health. Results from existing studies were inconsistent. Health effect of exposure to pet allergens may also be influenced by the type of pet and where the pets are kept. For instance, in some cultures children may sleep in the same bed with their pets, whereas in other cultures pets are kept out of homes with children. While some studies indicated dog ownership as a predictor for increased house dust endotoxin levels (El Sharif et al., 2004; Gehring et al., 2004; Waser et al., 2005), contrary observations have been reported (Lau et al., 2005). Cat-keeping had also been associated with increased levels of endotoxin in the home, but to a varying degree compared with dog ownership (El Sharif et al., 2004; Gehring et al., 2004; Platts-Mills et al., 2005). Roost et al. (1999) reported an association of keeping cats outdoors with an increased risk of sensitization to allergens. In China, pets are more popular in rural areas than in urban areas and are usually kept outdoors. In urban Chinese areas, most people live in apartments in concrete residential buildings and pets are usually kept indoors. In our study of urban Chinese women, we observed that exposure to cats was associated with an increase likelihood of chronic bronchitis (POR = 1.70; 95%CI: 1.12–2.56, Table 3), and exposure to other pets was also associated with an increase odds of asthma (POR = 2.07; 95%CI: 1.18–3.64, Table 3). In other words, pet ownership was a risk factor for respiratory diseases among urban Chinese women. The inconsistent findings from prior research on pet ownership may be due to recall bias, variation in the duration of pet ownership, proximity of the pets to the home dwellers, and the age of disease onset. We also observed a positive association between recent home renovation and allergic rhinitis in urban Chinese women. Recent home

renovation has been associated with increased levels of formaldehyde and volatile organic compounds (VOCs) and indoor air pollutants (Raw et al., 2004). Substantial evidence indicated that painters had an increased risk for developing asthma and asthma-related and other respiratory symptoms (Wieslander et al., 1994; Mastrangelo et al., 1995). Residential paints are likely to off-gas VOCs with use in home renovation and the effects of these acute exposures are difficult to estimate, although off-gassing chemicals have been found several months after application (Jaakkola et al., 2004). Another study has shown that cough, shortness of breath, conjunctivitis and rhinitis were significantly higher in students (mean age: 20.7 years) exposed to home renovation than those who were not (Arbak et al., 2004). In their case–control study of adults, Jaakkola et al. (2006) reported a strong association of home renovation with an increased risk of allergic rhinitis. This supports preventive health measures to mitigate indoor environmental pollutant exposure, including effective ventilation, during periods of home renovation. Consistent to prior research, we observed that the humidifier use was significantly associated with increased odds of bronchitis, and the presence of mold or mildew in the home was associated with increased odds of both bronchitis and allergic rhinitis. It is likely that these two risk factors may be interrelated, as high levels of humidity and moisture in the home may increase the prevalence of bacterial and fungal species. Several other studies have reported the association between humidifier use and bacterial contamination, promotion of mold and mildew growth in a warm, humid indoor environment (Dales et al., 2008; Jaakkola et al., 2002; Fisk et al., 2010; Mendell et al., 2011). Our results showed no association of indoor coal combustion with respiratory diseases after controlling for confounders, which was similar to the findings from the Four Chinese Cities Study (Zhang et al., 2002). In contrast to our study findings, earlier studies have reported an association of burning coal at home with decreased lung capacity and increased respiratory mortality and morbidity (Peabody et al., 2005; Barry et al., 2010; Kurt et al., 2011; Kodgule and Salvi, 2012). The inconsistency in findings may be partly due to measurement error in respondents' different perceptions of indoor coal combustion. For example, it has been assumed that coal is dirty compared to other types of fuel and, with effective dilution ventilation, indoor air pollutants from coal combustion could be diluted and removed from the house. Similar to the findings from previous studies (Norbäck et al., 2011; Thomas et al., 2012; Weichenthal et al., 2011), we found that houses near the main road and the presence of visible mold and water damage in the home were potential risk factors for respiratory diseases. We found no significant association of ETS with studied respiratory diseases after adjusted other co-variables. However, our findings were limited to females only. It has been noted that adult female populations are relatively insensitive to the effects of ETS in population surveys regarding respiratory health (Dong et al., 2011a,b; Syvanes et al., 2004; Martinez et al., 1988). Results from ECYHS (Syvanes et al., 2004) showed that, ETS exposure was associated with respiratory symptoms in men only. In boys, exposure to ETS had increased bronchial responsiveness (BR) (OR = 4.3; 95%CI 1.4–12.9) (Martinez et al., 1988). A possible explanation of the differences between men and women in their association of ETS exposure with respiratory diseases might be due to the gender differences in the development of their airways (Polgar and Weng, 1979; Becklake and Kauffmann, 1999). In our previous study, approximately 51–71% of households used coal for heating or cooking (Qian et al., 2000). Urban China is undergoing rapid economic and environmental transition. Residential energy consumption characteristics have changed substantially as natural gas and electricity have largely replaced solid fuels in urban Chinese households. Thus, the composition and concentration of both indoor and outdoor air pollution have changed. Exposure to indoor household air pollution appears to have decreased on the whole, whereas exposure

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to some outdoor air pollutants may have increased. This change in exposure characteristics is noteworthy, and previous exposure may well have contributed to the observed respiratory health outcomes of this study. However, due to the cross-sectional nature of the study, it is not possible to address temporality and differentiate between periods of varying exposure sources and characteristics. Although the observed respiratory health outcomes of this study likely represent accumulated exposure, we could address only presently observed risk factors. Surprisingly, fewer than 25% of tested residential associations were statistically significant. One possible explanation is open windows, especially during the summer season when high level ambient air pollutants could diffuse or be blown into the homes. Thus, ambient air pollution might be dominant, making indoor pollution emission sources less significant. It has been widely accepted that proximity to a roadway results in greater exposure to ambient air pollution, especially exposure to vehicle exhaust. The observed significant associations between house near major road and all health outcomes also support that dominant health effects of ambient air pollution might exist. The reported prevalence of asthma, chronic bronchitis, and allergic rhinitis was low (Table 1). It was possible that a considerable number of cases may have not been reported due to the self-reporting nature of data collection employed in this study. Assuming equal methodological errors between high and low exposure groups, the result would be greater similarity between groups and estimated PORs biased toward the null. Thus, effect estimates in the present study may be conservative. Several limitations of this study should be noted. First, the study design was a cross-sectional which precludes any causal inferences between exposure and outcome. Second, because responses were obtained through a questionnaire, recall bias could not be ruled out. However, the majority of the exposures were related to physical characteristics of resident homes rather than the more prone to recall biased behaviors or rare events. Misclassification bias was also a potential issue since the exposure and disease histories were selfreported. If present, it is likely non-differential which would bias the point estimate toward the null value. Residual confounding might also be present including lack of data on the seasonal patterns in the effect of indoor air pollution on respiratory diseases. In conclusion, respiratory diseases were related to indoor environmental risk factors including recent home renovation, pet ownership, humidifier use, presence of mold, cockroach infestation in the home, and residence near roadways and air pollution point sources. Further research is needed to address the etiologic relationships and public health implications of these findings. This study, along with the further studies which address the aforementioned limitations, should be conducted in other environments with different populations. If evidence continues to support our findings, preventive measures are therefore called for to reduce the impact of these risk factors to protect respiratory health. Prevention and remediation of potential indoor environmental pollutants may be a beneficial practice to reduce risks of respiratory disorders. Conflict of interest Authors report no conflict of interest. Authors are alone responsible for the content and writing of the paper. Acknowledgments The authors would like to thank everyone who participated in the survey for their invaluable time and contribution. This work was funded by the China Environmental Protection Foundation (CEPF2008-123-1-5). References Anandan C, Nurmatov U, van Schayck OC, Sheikh A. Is the prevalence of asthma declining? Systematic review of epidemiological studies. Allergy 2010;65(2):152–67.

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