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

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Residential characteristics and household risk factors and respiratorydiseases 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, Chinab Department of Occupational and Environmental Health, School of Public Health, China Medical University, Shenyang, Liaoning Province 110001, Chinac Department of Epidemiology, School of Public Health, Saint Louis University, Saint Louis, MO 63104, USAd Department of Biostatistics, School of Public Health, Saint Louis University, Saint Louis, MO 63104, USAe Guangdong Provincial Institute of Public Health, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou, Guangdong Province 510300, Chinaf Department of Epidemiology, School of Public Health, Sun Yat-sen University, Guangzhou 510080, Chinag Department of Ambient Air Pollution Monitor, Shenyang Environmental Monitoring Center, Shenyang, Liaoning Province 110014, Chinah Department of Environmental and Occupational Health School of Public Health, Saint Louis University, Saint Louis, MO 63104, USA

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.

⁎ Corresponding author at: Department of EpidemiologLouis University, Salus Center/Room 473, 3545 LafayetteUSA. Tel.: +1 314 977 8158; fax: +1 314 977 3234.

E-mail address: zqian2@slu.edu (Z.(M.) Qian).

0048-9697/$ – see front matter © 2013 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.scitotenv.2013.05.063

a b s t r a c t

a r t i c l e i n f o

Article history:

Received 3 January 2013Received in revised form 2 May 2013Accepted 13 May 2013Available online 29 June 2013

Editor: Xuexi Tie

Keywords:Residential characteristicsIndoor environmental risk factorsWomenRespiratory diseasesChina

Background: Few studies have assessed the impact of residential home characteristics and home environmentalrisk factors on respiratory diseases in Chinese women. Therefore, this study sought to determine the associationbetween residential home features, domestic pets, home renovation and other indoor environmental riskfactors 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 25districts of seven cities in Liaoning Province, Northeast China. Information on respiratory health, residentialcharacteristics, and indoor air pollution sources was obtained by a standard questionnaire from the AmericanThoracic 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 airpollution 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 wasassociated 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 increasedlikelihood of respiratory morbidity among Chinese women.

© 2013 Elsevier B.V. All rights reserved.

y, School of Public Health, SaintAvenue, Saint Louis, MO 63104,

rights reserved.

1. Introduction

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

390 G.-H. Dong et al. / Science of the Total Environment 463–464 (2013) 389–394

few decades, in recent years developing countries have witnessed anincrease 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 indicatedthat indoor air pollution is a key environmental risk factor contributingto 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 betweenchronic airflow obstruction in adults in developing countries, includ-ing China, with exposure to indoor air pollution resulting from thecombustion 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 Chinaover the past decade have been marked by massive constructionand modernization projects as well as increased individual wealth.This economic boom has fueled new construction of large apartmentcomplexes in addition to an increased demand for home renovation.During renovation, Chinese home dwellers' potential exposure to in-door air pollution is elevated either from the demolition process orfrom the new materials (Dong et al., 2008, 2011a). Meanwhile, withthe improvement of the standard of living in China, the levels ofindoor pollution from coal smoke have decreased rapidly as morepeople move to new homes supplied with gas and/or electric power(Dong et al., 2011b). Nonetheless, exposures to domestic pets andtobacco smoke remain a potential source of indoor air pollutants formany Chinese residents. Few research have investigated the healtheffects of indoor air pollution related to various features of the residen-tial home environment (e.g., pet ownership, history of home renova-tion, humidifier use, and proximity to the road, factory, smokestack)on respiratory symptoms or diseases in Chinese women. Women inChina are often in charge of domestic duties such as cooking whichincreases their exposure to air pollutants more than men. Therefore,the objective of the present study was to identify associations betweenindoor air pollution and respiratory diseases in urban adult Chinesewomen.

2. Methods

2.1. Site selection and subject recruitment

The study participants were 31,049 mothers of schoolchildren whohad participated in a parallel cross-sectional study of the effects of out-door and indoor air pollution on respiratory health among children(Dong et al., 2013). The mothers resided in seven cities of the northeastChina, i.e. Shanyang, Dalian, Anshan, Fushun, Benxi, Liaoyang andYingkou, and each was asked to fill out a questionnaire. The sevencities were chosen to ensure varying levels of environmental pollu-tion, socio-economic conditions, and types of manufacturing indus-tries. There were five districts in Shenyang, four districts in Dalianand Fushun, and three districts in Anshan, Benxi, Liaoyang andYingkou (25 districts in total). An elementary school (n = 25) andtwo kindergartens (n = 50) were randomly selected from eachdistrict under the condition that the district was within 1 km of anenvironmental monitoring station. Children at these institutionswere asked to give a questionnaire handout and attached endorsedconsent form to their parents or guardians to complete. All proce-dures were approved and in compliance with the ethical standardsof the responsible committee on human experimentation of theChina Medical University as well as the principles outlined in theHelsinki Declaration. Consent forms were obtained from partici-pants who completed and returned the questionnaire.

There were a total of 35,527 children from 25 elementary schoolsand 50 kindergartens, of whom 31,649 had their mothers completethe questionnaire, yielding an overall response rate of 89.1%. The par-ticipation rate varied from 81.3% in Yingkou to 94.7% in Dalian and

was not correlated with disease prevalence. 869 mothers were exclud-ed from the study, including 600who had less than 3 years of residenceand 269 who had missing and/or “Not applicable” responses.

2.2. Questionnaire survey

A self-administered questionnaire collected information on theresidential history, type of dwelling (flat, terraced, semi-detachedor detached), details of renovations of dwelling within the past2 years (if any), sources of heat and light, fuels for cooking, the lo-cation of kitchen, types of ventilators, women's respiratory ill-nesses and symptoms and other medical history, education levelsand smoking status of each member of the household in April2009. The questionnaire was adapted from the American ThoracicSociety (ATS) questionnaire. After reviewing the questionnaire,parents/guardians were invited to a Parents' Night to learn detailedinformation about the survey, including the objectives of the studyand instructions on filling out the questionnaire. Parents whowished to complete the questionnaire at home were asked tohave their child return the completed questionnaire in an envelopeto the teacher. A standardized protocol was strictly followed fordata entry and data management across all study sites (Qian etal., 2000; Dong et al., 2013).

The primary outcomes of interest are respiratory medical condi-tions. We focused on three types of respiratory diseases — asthma,chronic bronchitis, and allergic rhinitis. Asthma was defined by thequestion “Has a doctor ever diagnosed the mother with asthma?”);chronic bronchitis was defined by the question “Has a doctor ever diag-nosed the mother with chronic bronchitis?”; and allergic rhinitis wasdefined by the question “Has a doctor ever diagnosed the mother withallergic rhinitis?”. Environmental tobacco smoke (ETS) exposure wasdefined by the answer “Yes” to the question “Does anyone who livingin the same house smoke cigarettes daily in this home?” Home renova-tion refers to the following activities in a homewithin the past 2 years:installation of polyvinyl chloride (PVC) flooring, hardwood floor, wall-paper, latex paints or plastic wall materials, new furniture, or syntheticcarpet; the application of oil-based paints, or others (window or doorreplacement, aluminum and iron grills; roofing; plumbing; or electricalwork).

2.3. Statistical methods

Descriptive analysis was used to characterize the study sample. Datawere tested for normality (using the Shapiro–Wilk W-test) and homo-geneity (using Bartlett's test for unequal variances). In each group, themean ± SD was calculated for continuous variables, and frequencieswere calculated for categorical variables. Chi square test statisticswere calculated to assess associations between categorical variables.The associations between indoor air pollution and respiratory diseaseswere estimated by logistic regression models. Prevalence odds ratios(POR) and their 95% confidence intervals (95%CI) were calculated forindoor air pollution exposure adjusted by covariables of age, sex, andstudy district. The data were analyzed by the GLIMMIX procedureusing the SAS software (version 9.2; SAS Institute, Cary, N.C., USA) toaccount for the cluster structure of the data. All statistical tests weretwo-tailed, and p values less than 0.05 were considered statisticallysignificant.

3. Results

Among the 30,780 mothers with valid responses, the prevalencerates of asthma, bronchitis and allergic rhinitis were 0.71%, 1.20% and1.97%, respectively (Table 1). Higher prevalence of respiratory diseasewas associated with a parental history of respiratory diseases, types ofhome, number of rooms in the house, with proximity to a main roador an industrial factory or smokestack.

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

N AsthmaN(%)

ChronicbronchitisN(%)

AllergicrhinitisN(%)

Environmental tobacco smokeNo 15,733 83(0.53) 147(0.93) 254(1.61)Yes 15,047 135(0.90)a 222(1.48)a 351(2.33)a

Home renovation in the past 2 yearsNo 20,300 137(0.67) 251(1.24) 345(1.70)Yes 10,480 81(0.77) 118(1.13)a 260(2.48)a

Household petsNo 25,952 173(0.67) 285(1.10) 511(1.97)Yes 4828 45(0.93)a 84(1.74)a 94(1.95)

Number of pets0 25,952 173(0.67) 285(1.10) 511(1.97)1 3849 37(0.96)a 65(1.69)a 69(1.79)≥2 979 8(0.82) 19(1.94)a 25(2.55)

Type of petsCat 1273 5(0.39) 26(2.04)a 27(2.12)Dog 1632 18(1.10)a 31(1.90)a 31(1.90)Birds 837 6(0.72) 16(1.91)a 12(1.43)Farm animals 563 4(0.71) 8(1.42) 16(2.84)Others 1001 14(1.40)a 13(1.30) 18(1.80)

Window left open in winterNo 12,516 102(0.81) 175(1.40) 252(2.01)Yes 18,264 116(0.64) 194(1.06)a 353(1.93)

Humidifier useNo 26,209 182(0.69) 310(1.18) 512(1.95)Yes 4571 36(0.79) 59(1.29) 93(2.03)

Indoor coal combustion heating

391G.-H. Dong et al. / Science of the Total Environment 463–464 (2013) 389–394

The prevalence rate of respiratory diseases by indoor environmentalrisk factors is provided in Table 2.Womenexposed to ETShad significant-ly 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 whowere not exposed to ETS. Women living in homes renovated recentlyhad a lower prevalence of chronic bronchitis (1.13 vs 1.24) but a higherprevalence of allergic rhinitis (2.48% vs. 1.70%) than those living innon-renovated homes. Women who were exposed to pets had higherprevalence 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 ofasthma for women exposed to a single pet at home was higher thanthose who had no pet at home and the prevalence of chronic bronchitisseemed to increase with the number of pets. Womenwhowere exposedto dogs had higher prevalence rates of asthma and chronic bronchitisthan those who were not, and women who were exposed to cats had ahigher prevalence of bronchitis than those who were not. Furthermore,indoor coal combustion, ventilator use, smoke from cooking, and mold/mildewor cockroaches in the home in the past 12 monthswere associat-ed with increased rates of respiratory morbidities, whereas the preva-lence of chronic bronchitis was lower (1.06% vs. 1.40%) for womenliving in homes with windows left open in winter.

All statistically significant associations are indicated in bold typefacein Table 3. After controlling for potential confounders, home renovationin the past 2 yearswas significantly associatedwith an increased odds ofallergic rhinitis (POR = 1.39; 95%CI 1.17–1.64). Pet ownership was sig-nificantly 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 1Distribution of respiratory diseases by house types, locations and demographics amongChinese women in Liaoning Province, Northeast China (n = 30,780).

N AsthmaN(%)

ChronicbronchitisN(%)

AllergicrhinitisN(%)

Total 30,780 218(0.71) 369(1.20) 605(1.97)City

Shenyang 8662 67(0.77) 80(0.92) 159(1.84)Dalian 4901 35(0.71) 68(1.39) 110(2.24)Anshan 4158 26(0.63) 49(1.18) 62(1.49)Fushun 3254 27(0.83) 63(1.94) 63(1.94)Benxi 2641 23(0.87) 39(1.48) 69(2.61)Liaoyang 3174 19(0.60) 26(0.82) 52(1.64)Yingkou 3990 21(0.53) 44(1.10) 90(2.26)

Education levelbHigh school 8353 66(0.79) 117(1.40) 134(1.60)≥High school 22,427 152(0.68) 252(1.12)⁎ 471(2.10)⁎

Parental history of atopya

No 29,342 168(0.58) 312(1.06) 482(1.64)Yes 1438 49(3.41)⁎ 57(3.96)⁎ 123(8.55)⁎

Parental history of bronchitisNo 30,057 193(0.64) 319(1.06) 553(1.84)Yes 723 25(3.46)⁎ 50(6.92)⁎ 52(7.19)⁎

House typeApartment 27,926 188(0.67) 326(1.17) 563(2.02)Othersb 2854 30(1.05)⁎ 43(1.51) 42(1.47)⁎

Room number in homeb3 14,286 95(0.66) 137(0.96) 312(2.18)≥3 16,494 123(0.75) 232(1.41)⁎ 293(1.78)⁎

House near major roadNo 18,885 115(0.61) 191(1.01) 327(1.73)Yes 11,895 103(0.87)⁎ 178(1.50)⁎ 278(2.34)⁎

House near a factoryNo 28,233 191(0.68) 330(1.17) 552(1.96)Yes 2547 27(1.06)⁎ 39(1.53) 53(2.08)

House near a smokestackNo 25,798 172(0.67) 292(1.13) 478(1.85)Yes 4982 46(0.92)⁎ 77(1.55)⁎ 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.

No 28,759 195(0.68) 327(1.14) 569(1.98)Yes 2021 23(1.14)a 42(2.08)a 36(1.78)

Ventilator useNo 5189 51(0.98) 88(1.70) 83(1.60)Yes 25,591 167(0.65)a 281(1.10)a 522(2.04)a

Smoke from cookingNo 29,885 210(0.70) 349(1.17) 582(1.95)Yes 895 8(0.89) 20(2.23)a 23(2.57)

Mold/mildew in the past 12 monthsNo 27,554 194(0.70) 312(1.13) 521(1.89)Yes 3226 24(0.74) 57(1.77)a 84(2.60)a

Cockroaches in the past 12 monthsNo 17,115 93(0.54) 168(0.98) 275(1.61)Yes 13,665 125(0.91) 201(1.47)a 330(2.41)a

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 increasedodds of chronic bronchitis (OR = 1.70; 95%CI: 1.12–2.56). Residing inhomes along a main road was associated with an increased likelihoodof 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 ofchronic bronchitis (POR = 1.44; 95%CI: 1.07–1.94). In addition, expo-sure to cockroaches in the past 12 months and mold/water damagein the homewere both associated with an increased likelihood of respi-ratory diseases. There was no significant association between theprevalence of respiratory diseases and ETS exposure, indoor coal com-bustion, ventilator use, and smoke from cooking.

4. Discussion

In the present study, several indoor environmental factors wereassociated with increased prevalence of one or more of the studied re-spiratory illnesses in urban Chinese women. Specifically, we observed:(1) pet ownership, humidifier use, and presence of three or morerooms in the homewere associatedwith increased prevalence of chronicbronchitis, (2) home renovation was associated with increased preva-lence of allergic rhinitis, and (3) residing close to a main road, which re-flects exposure to outdoor air pollution, and the presence of mold and

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

Asthma Chronicbronchitis

Allergic rhinitis

House near major road 1.34 (1.02, 1.76) 1.34 (1.09, 1.66) 1.24 (1.05, 1.46)House near factory 1.44 (0.86, 2.42) 0.74 (0.48, 1.15) 0.74 (0.52, 1.05)House near chimney 1.24 (0.87, 1.79) 1.19 (0.89, 1.58) 1.29 (1.04, 1.60)Three or more rooms inhouse

1.04 (0.78, 1.39) 1.37 (1.09, 1.72) 0.85 (0.72, 1.02)

Environmental tobaccosmoke

1.32 (0.96, 1.80) 1.22 (0.96, 1.56) 1.17 (0.97, 1.41)

Home renovation withinthe past 2years

1.23 (0.92, 1.64) 0.98 (0.78, 1.24) 1.39 (1.17, 1.64)

Household pets 1.18 (0.84, 1.66) 1.40 (1.09, 1.81) 0.92 (0.73, 1.16)Number of petsb

1 1.25 (0.87, 1.81) 1.38 (1.05, 1.83) 0.88 (0.68, 1.14)≥2 0.95 (0.46, 1.97) 1.48 (0.91, 2.41) 1.05 (0.69, 1.60)

Type of petsb

Cat 0.51 (0.21, 1.25) 1.70 (1.12, 2.56) 0.98 (0.66, 1.46)Dog 1.24 (0.74, 2.08) 1.39 (0.93, 2.06) 0.93 (0.64, 1.36)Birds 0.96 (0.42, 2.19) 1.62 (0.97, 2.72) 0.66 (0.37, 1.18)Farm animals 0.74 (0.27, 2.04) 0.94 (0.45, 1.94) 1.20 (0.71, 2.03)Others 2.07 (1.18, 3.64) 1.13 (0.64, 2.01) 0.82 (0.51, 1.33)

Window left open inwinter 0.83 (0.63, 1.11) 0.83 (0.67, 1.03) 0.92 (0.78, 1.10)Humidifier use 1.27 (0.87, 1.86) 1.44 (1.07, 1.94) 1.01 (0.80, 1.28)Coal combustion 1.14 (0.64, 2.05) 1.52 (0.98, 2.36) 1.07 (0.70, 1.64)Ventilator use 0.79 (0.53, 1.16) 0.82 (0.61, 1.10) 1.08 (0.82, 1.41)Smoke from cooking 0.93 (0.44, 1.93) 1.51 (0.93, 2.44) 1.05 (0.68, 1.64)Mold or mildew presencein the past 12 months

0.70 (0.42, 1.17) 1.50 (1.05, 2.15) 1.37 (1.04, 1.81)

Cockroaches in the past12 months

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, housetype, and city of residence.

b Reference category = no pet ownership.

392 G.-H. Dong et al. / Science of the Total Environment 463–464 (2013) 389–394

cockroaches in the home, were also associatedwith respiratory diseases.ETS exposurewas not associatedwith any respiratory disease of interest.

It has been controversial as to whether or not pet ownership pre-vents specific allergic sensitization or reduces the risk of respiratorydiseases. There has been little literature about the effect of pet owner-ship on adult respiratory health. Results from existing studies wereinconsistent. Health effect of exposure to pet allergens may also beinfluenced by the type of pet and where the pets are kept. Forinstance, in some cultures children may sleep in the same bed withtheir pets, whereas in other cultures pets are kept out of homeswith children. While some studies indicated dog ownership as a pre-dictor for increased house dust endotoxin levels (El Sharif et al., 2004;Gehring et al., 2004; Waser et al., 2005), contrary observations havebeen reported (Lau et al., 2005). Cat-keeping had also been associatedwith increased levels of endotoxin in the home, but to a varyingdegree 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 outdoorswith an increased risk of sensitization to allergens. In China, pets aremore popular in rural areas than in urban areas and are usually keptoutdoors. In urbanChinese areas,most people live in apartments in con-crete residential buildings and pets are usually kept indoors. In ourstudy of urban Chinese women, we observed that exposure to catswas associated with an increase likelihood of chronic bronchitis(POR = 1.70; 95%CI: 1.12–2.56, Table 3), and exposure to other petswas also associated with an increase odds of asthma (POR = 2.07;95%CI: 1.18–3.64, Table 3). In otherwords, pet ownershipwas a risk fac-tor for respiratory diseases among urban Chinesewomen. The inconsis-tent findings from prior research on pet ownershipmay be due to recallbias, variation in the duration of pet ownership, proximity of the pets tothe home dwellers, and the age of disease onset.

We also observed a positive association between recent home reno-vation and allergic rhinitis in urban Chinese women. Recent home

renovation has been associated with increased levels of formaldehydeand volatile organic compounds (VOCs) and indoor air pollutants(Raw et al., 2004). Substantial evidence indicated that painters had anincreased risk for developing asthma and asthma-related and other re-spiratory symptoms (Wieslander et al., 1994; Mastrangelo et al., 1995).Residential paints are likely to off-gas VOCs with use in home renova-tion and the effects of these acute exposures are difficult to estimate,although off-gassing chemicals have been found several months afterapplication (Jaakkola et al., 2004). Another study has shown thatcough, shortness of breath, conjunctivitis and rhinitis were significantlyhigher in students (mean age: 20.7 years) exposed to home renovationthan those who were not (Arbak et al., 2004). In their case–controlstudy of adults, Jaakkola et al. (2006) reported a strong association ofhome renovation with an increased risk of allergic rhinitis. This sup-ports preventive health measures to mitigate indoor environmentalpollutant exposure, including effective ventilation, during periods ofhome renovation.

Consistent to prior research, we observed that the humidifier usewas significantly associated with increased odds of bronchitis, and thepresence of mold or mildew in the homewas associatedwith increasedodds of both bronchitis and allergic rhinitis. It is likely that these tworisk factorsmay be interrelated, as high levels of humidity andmoisturein the homemay increase the prevalence of bacterial and fungal species.Several other studies have reported the association between humidifieruse and bacterial contamination, promotion of mold and mildewgrowth 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 withrespiratory diseases after controlling for confounders, which was sim-ilar to the findings from the Four Chinese Cities Study (Zhang et al.,2002). In contrast to our study findings, earlier studies have reportedan association of burning coal at home with decreased lung capacityand 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 measurementerror in respondents' different perceptions of indoor coal combustion.For example, it has been assumed that coal is dirty compared to othertypes of fuel and, with effective dilution ventilation, indoor air pollut-ants from coal combustion could be diluted and removed from thehouse.

Similar to the findings from previous studies (Norbäck et al., 2011;Thomas et al., 2012; Weichenthal et al., 2011), we found that housesnear the main road and the presence of visible mold and water dam-age in the home were potential risk factors for respiratory diseases.We found no significant association of ETS with studied respiratorydiseases after adjusted other co-variables. However, our findingswere limited to females only. It has been noted that adult female pop-ulations are relatively insensitive to the effects of ETS in populationsurveys regarding respiratory health (Dong et al., 2011a,b; Syvaneset al., 2004; Martinez et al., 1988). Results from ECYHS (Syvanes etal., 2004) showed that, ETS exposure was associated with respiratorysymptoms in men only. In boys, exposure to ETS had increased bron-chial responsiveness (BR) (OR = 4.3; 95%CI 1.4–12.9) (Martinez etal., 1988). A possible explanation of the differences between menand women in their association of ETS exposure with respiratorydiseases might be due to the gender differences in the developmentof their airways (Polgar and Weng, 1979; Becklake and Kauffmann,1999).

In our previous study, approximately 51–71% of households usedcoal for heating or cooking (Qian et al., 2000). Urban China is undergo-ing rapid economic and environmental transition. Residential energyconsumption characteristics have changed substantially as natural gasand electricity have largely replaced solid fuels in urban Chinese house-holds. Thus, the composition and concentration of both indoor andoutdoor air pollution have changed. Exposure to indoor household airpollution appears to have decreased on the whole, whereas exposure

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to some outdoor air pollutants may have increased. This change inexposure characteristics is noteworthy, and previous exposure maywell have contributed to the observed respiratory health outcomes ofthis study. However, due to the cross-sectional nature of the study, itis not possible to address temporality and differentiate between periodsof varying exposure sources and characteristics. Although the observedrespiratory health outcomes of this study likely represent accumulatedexposure, we could address only presently observed risk factors.

Surprisingly, fewer than 25% of tested residential associations werestatistically significant. One possible explanation is openwindows, espe-cially during the summer season when high level ambient air pollutantscould diffuse or be blown into the homes. Thus, ambient air pollutionmight be dominant, making indoor pollution emission sources less sig-nificant. It has beenwidely accepted that proximity to a roadway resultsin greater exposure to ambient air pollution, especially exposure to vehi-cle exhaust. The observed significant associations between house nearmajor road and all health outcomes also support that dominant healtheffects of ambient air pollution might exist.

The reported prevalence of asthma, chronic bronchitis, and allergicrhinitis was low (Table 1). It was possible that a considerable numberof cases may have not been reported due to the self-reporting natureof data collection employed in this study. Assuming equal methodolog-ical errors between high and low exposure groups, the result would begreater similarity between groups and estimated PORs biased toward thenull. Thus, effect estimates in the present study may be conservative.

Several limitations of this study should be noted. First, the studydesign was a cross-sectional which precludes any causal inferencesbetween exposure and outcome. Second, because responses wereobtained through a questionnaire, recall bias could not be ruled out.However, the majority of the exposures were related to physicalcharacteristics of resident homes rather than the more prone to recallbiased behaviors or rare events. Misclassification bias was also a po-tential issue since the exposure and disease histories were self-reported. If present, it is likely non-differential which would biasthe point estimate toward the null value. Residual confoundingmight also be present including lack of data on the seasonal patternsin the effect of indoor air pollution on respiratory diseases.

In conclusion, respiratory diseases were related to indoor environ-mental 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. Furtherresearch is needed to address the etiologic relationships and publichealth implications of these findings. This study, along with the furtherstudies which address the aforementioned limitations, should beconducted in other environments with different populations. If evi-dence continues to support our findings, preventive measures aretherefore called for to reduce the impact of these risk factors to protectrespiratory health. Prevention and remediation of potential indoorenvironmental pollutants may be a beneficial practice to reduce risksof respiratory disorders.

Conflict of interest

Authors report no conflict of interest. Authors are alone responsiblefor the content and writing of the paper.

Acknowledgments

The authors would like to thank everyone who participated in thesurvey for their invaluable time and contribution. This work was fundedby the China Environmental Protection Foundation (CEPF2008-123-1-5).

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