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Association between indoor air pollution measurements and

respiratory health in women and children in Lao PDR

Introduction

There is a well-established association between ambientair pollution and adverse health outcomes in developedand developing countries (WHO 2001, 2002; Schwartz,1994). Owing to the substantially longer time periodsspent indoors where dispersal of pollutants may bepoor, indoor air pollution can pose many hundreds oftimes greater exposure than outdoor air pollution(Bruce et al., 2000). Indoor air pollution is of partic-ular concern for women and children in developing

countries (Bruce et al., 2000; Smith and Mehta, 2003;Ezzati, 2005; Rinne et al., 2007), where up to 90% ofrural households cook and heat using unprocessedbiomass such as dung, crop residues, wood andcharcoal (Bruce et al., 2000). A number of studieshave identified indoor use of biomass fuel as a majorcontributor to indoor air pollution (Zhang and Smith,1999; Wornat et al., 2001; Oanh et al., 1999; Daiseyet al., 1989; Fischer and Koshland, 2007), which isclaimed to account for 2.2–2.8 million deaths annuallyin developing countries (Tuckett et al., 1998). Indeed,

Abstract This article presents the results of a study on the association betweenmeasured air pollutants and the respiratory health of resident women and chil-dren in Lao PDR, one of the least developed countries in Southeast Asia.The study, commissioned by the World Health Organisation, included PM10, COand NO2 measurements made inside 181 dwellings in nine districts within twoprovinces in Lao PDR over a 5- month period (12/05–04/06), and respiratoryhealth information (via questionnaires and peak expiratory flow rate (PEFR)measurements) for all residents in the same dwellings. Adjusted odds ratios werecalculated separately for each health outcome using binary logistic regression.There was a strong and consistent positive association between NO2 and CO foralmost all questionnaire-based health outcomes for both women and children.Women in dwellings with higher measured NO2 had more than triple of the oddsof almost all of the health outcomes, and higher concentrations of NO2 and COwere significantly associated with lower PEFR. This study supports a growingliterature confirming the role of indoor air pollution in the burden of respiratorydisease in developing countries. The results will directly support changes inhealth and housing policy in Lao PDR.

K. Mengersen1, L. Morawska2,H. Wang2, N. Murphy1,F. Tayphasavanh3, K. Darasavong3,N. S. Holmes2

1School of Mathematical Sciences, QueenslandUniversity of Technology, Brisbane, Qld, Australia,2International Laboratory for Air Quality and Health,Queensland University of Technology, Brisbane, Qld,Australia, 3Ministry of Health, Vientiane, Laos

Key words: Indoor air pollution; Developing countries;Respiratory health outcome; Pulmonary disease;Exposure; Statistical association.

L. MorawskaInternational Laboratory for Air Quality and HealthQueensland University of Technology2 George Street, BrisbaneQld 4001, AustraliaTel.: +61 7 3138 2616Fax: +61 7 3138 9079e-mail: [email protected]

Received for review 28 October 2009. Accepted forpublication 2 July 2010.

Practical ImplicationsThis is the first study that investigated indoor air quality and its impact within residential dwellings in Lao PDR,which is one of the poorest and least developed countries in south-east Asia, with a life-expectancy of 56 years in 2008.While there have been other studies published on indoor air quality in other developing countries, the situation inLaos is different because the majority of houses in Laos used wood stoves, and therefore, emissions from woodburning are the dominant sources of indoor air pollution. In other countries, and studies, while emission from woodburning was investigated, wood was rarely the main or the only fuel used, as the houses used in addition (or solely)dung, kerosene or coal. The study quantified, for the first time, concentrations in houses two provinces in Laos PDRand shed light on the impact of human activities and urban design on pollutant concentrations and respiratory health.This study contributes to the accumulation of evidence to provide more reliable estimates of risk and a more informedbasis for decision-making by concerned governments and communities.

Indoor Air 2011; 21: 25–35www.blackwellpublishing.com/inaPrinted in Singapore. All rights reserved

� 2010 John Wiley & Sons A/S

INDOOR AIRdoi:10.1111/j.1600-0668.2010.00679.x

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the household use of solid fuels has been claimed as thelargest single environmental cause of ill health (Smithet al., 2005).Poor indoor air quality in general and the use of

biomass fuels for cooking and heating in particular havebeen shown to be associated with reduced lung functionwhich, in turn, has been linked to short- and long-termrespiratory and cardiac illnesses, particularly in womenand children (Smith et al., 2005; Desai et al., 2004; Karaet al., 2003; Ozbay et al., 2001; Rudan et al., 2008;Dherani et al., 2008; Liu et al., 2007; Diaz et al., 2007).Carbon monoxide (CO), nitrogen dioxide (NO2), par-ticulate matter (PM) and other chemicals have beenconfirmed in relationships between biomass fuel andadverse respiratory health (Rinne et al., 2007; Dionisioet al., 2008; Franklin, 2007; Rumchev et al., 2007; Liuet al., 2008; Koistinen et al., 2008; Kumar et al., 2007).Biological mechanisms for the effect of biomass smokeon lower respiratory infections in children, and math-ematical modelling of intake of pollutants from episodicemissions have also been considered (Grigg, 2007;Nazaroff, 2008). These associations are potentiallymodified by biological contaminants such as dust, pets,damp and mould, as well as other chemical contami-nants such as tobacco smoke, off-gassing emissions,other carcinogens, gender and age (Wigle et al., 2007;Dales et al., 2008). The instruments used for determin-ing respiratory health, which include clinical measuressuch as hospital admission, questionnaire-based assess-ment, or direct measurements such as forced expiratoryvolume, may also impact on the observed results (Eptonet al., 2008).This article reports on a study of the association

between measured air pollutants in residences in LaoPDR, and the reported respiratory health and mea-sured lung function of women and children who livedin these residences. The study also evaluates thecontribution of relevant indoor air activities, includingtime spent near a cooking place and near a fire, dustinside and outside, smoking and drying clothes inside.This is part of a larger epidemiological and measure-ment study, detailed in Methods. The Lao populationis distinguished by a number of factors that impactsubstantially on this association. The population is themost rural in south-east Asia, and wood is almostuniversally used for cooking. However, the climate ismore temperate than many other countries in whichsimilar studies have been conducted, and the majorityof houses are well ventilated because of their construc-tion from wood or bamboo (see Figure 1).

Methods

Study design

The study was comprised of a case–control studyembedded in a cross-sectional study and was designed

in collaboration with thirteen representatives of theLao Ministry of Health, the National Statistics Centreand the Science, Technology and EnvironmentalAgency. Participants in the study were chosen accord-ing to a cluster design comprising two provinces, ninedistricts within these provinces and 20 hospitals orhealth centres within the districts. Six districtsfrom Vientiane province (Phonhong, Mad, Feuang,Thoulakhom, Kasy and Vangvieng) and three fromBorikhamxay province (Bolikhanh, Khamkeut andPakkading) were chosen to meet the prerequisites ofwide representation of ethnic groups, wide range ofhousing characteristics, high prevalence of respiratoryillness, accessibility and adequate staff resources. Foreach province, a list of hospitals, health centres,villages and village population within each districtwas obtained from the National Statistics Centre. Atotal of 20 health centres were selected as follows: 12from Vientiane province (Thoulakhom (3), Phonhong(1), Kasy (1), Vangvieng (3), Feuang (3), Mad (1)) and8 from Bolikhamxay province (Bolikhanh (2), Pakk-ading (2), Khamkeut (4)).For each health centre (or group of centres), four

children admitted for acute respiratory illness, aged 1–4 years sequentially from 1st October 2005, wereenrolled in the study. No more than two such childrenwere enrolled from any one village. One to twochildren were randomly selected from the same village(in a different house), matched by age, ethnic groupand location of kitchen. The houses in which thesechildren resided were included in the study. For eachhouse in the study, experimental measurements ofindoor air quality were taken. For each householdmember, lung function measurements and question-naire information related to indoor air factors, expo-sure and respiratory and cardiovascular health weregathered; details are provided in Sections Question-naire and Indoor air pollutants measurement below.

Fig. 1 An example of a typical Laos house

Mengersen et al.

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The study was designed to be conducted in the coolseason during which indoor exposure and respiratoryillness are potentially highest.

Questionnaire

A questionnaire was delivered to a representative ofeach household enrolled in the study. The survey wasconducted in 356 houses, including the 199 houses, inwhich the air-quality measurements were performed.The questionnaire was based on the American Tho-racic Society Questionnaire, the World Health Survey,World Bank approach, ISAAC questionnaire andWestern Australia Heart Survey, and critically evalu-ated by two international experts. Separate questionswere developed for children aged 1–4 years, youth aged5–14 years and adults. They were then tailored to localconditions and interests by the 13-member local team,many of whom have medical degrees and are profes-sionals in public health and environmental practice.The questionnaire was translated into Lao and pilotedin Pong Song.A small team of local health experts was selected to

administer the questionnaire to all households in thestudy. The team participated in the questionnairedevelopment, a prestudy training workshop and thepilot exercise.The questionnaire comprised six parts: interviewer

information, completed by the chief interviewer; a childhealth questionnaire for each child aged 1–4 years inthe household, completed by a parent or primary carer;a child health questionnaire for each child aged 5–14 years in the household, completed by a parent orprimary carer; an adult health questionnaire for eachadult in the household, completed by the adultsthemselves where possible or by a close relative orhead of the household; a household characteristicsquestionnaire, completed by the head of the household;and a town/village questionnaire, completed for eachcommunity by the community head, community healthworker or the head of the household.Questions on household characteristics focused on

indoor combustion sources, other exposures such assmoking and dust, and ventilation. Health questionsfocused on symptoms, medical diagnoses and hospi-talization associated with acute respiratory infectionsin the past 2 weeks, the past month and in the pastyear. Direct and indirect indoor, outdoor and occupa-tional exposures to pollutants were also solicited.

Indoor air pollutants measurement

Measurements of pollutants were conducted between23rd December 2005 and 14th April 2006. Measure-ments were made within the living area in eachdwelling for a period of 12 h, from 06:00 to 18:00from December to April (corresponding to the dry

season) during which cooler outdoor temperatureswere expected to result in higher indoor exposure andincidence of respiratory illness.Particle mass (PM10), nitrogen dioxide (NO2) and

carbonmonoxide (CO)weremeasuredwithin the housesusing a portable Escort ELF sampling pump (MSA),connected to a cyclone (PM10), long duration colourdetectionCO tubes (Draeger) andNO2 adsorption tubes(SKC 224-40-02). The cyclone contained preweighed0.8- lm pore PVC filters (MSA) through which the flowrate was adjusted to 1.7 l/min. After equilibrated in adesiccator (20�C, 65%RH), the filters were weighed on amicrobalance (Mettler Toledo), with an upper limit of3 g and 0.002 mg readability. The CO detection tubeswere designed for measurement of time-weighted aver-ageCOconcentration.The chemicals in the tubes changein colour in response to the presence of CO gas in thesample. By knowing the volume of sampled air, theamount of colour change can be translated into a veryaccurate measurement of the level of CO, described as apercentage of the total air or in parts per million (ppm).NO2 was sampled and analysed following the Occupa-tional Safety and Health Administration TechnicalManual (6014). In brief, NO2 was sampled by adsorp-tion onto two consecutive molecular sieve tubes treatedwith triethanolamine, which reacted with NO2 to formnitrite and nitrate ions. NO2 concentration was detectedusing aUV-Vis spectrometer (ThemoSpectronic) at k =540 nm to measure the sum of nitrite and nitrate ions.The location of instruments was chosen based on the

following constraints: (i) representative of the mainliving area of house; (ii) away from the sources; (iii)away from the windows and the doors; and (iv) safe forthe instrumentation and people.

Lung function measurement

Peak expiratory flow rate (PEFR, measured in l/min)was chosen as the indicative measure of lung functionin this study, because of its ability to detect moderateor severe airway obstruction, the simplicity of admin-istration, the portability of the measuring instrumen-tation and its applicability for a wide cross-section ofthe population.PEFR measurements were taken for each available

member of the household in which air pollutantmeasurements were made. Measurements were con-ducted by the same trained medical and health staff whoadministered the questionnaires, using a hand-heldPEFRmeter. The comparative unreliability of measure-ments obtained for children<5 years old was mitigatedto some extent by the careful conduct of the trained staff.

Statistical analysis

Statistical analysis of the association between indoorair pollutants and respiratory health was undertaken

Indoor air and respiratory health in Lao PDR

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using two types of respiratory health measures. Thefirst was based on the questionnaire responses and thesecond was based on lung function measurements.Analysis of respiratory health outcomes based on

questionnaire data focused on reported events in thepast 2 weeks and the past month for children 1–4 years, and the past month and the past 12 months forchildren aged 5–14 years and for women aged15+ years. Exploratory statistical analyses comprisedsummary statistics, plots and t-tests. Adjusted oddsratios were calculated for each health outcome sepa-rately using binary logistic regression, with the loga-rithm of the pollutant measurements as explanatoryvariables. Models were fit with and without a constant,and adjustment for age and gender of the children wasalso considered. Results are reported for modelswithout a constant or adjustment. Multivariate anal-yses of variance based on general linear models werealso performed to assess the main effects and interac-tions of housing characteristics on the three pollutantstogether, both within each province and for the twoprovinces combined.For the analysis of the association between indoor

air pollutant measurements and measured lung func-tion, children were categorized into three age groups(1–4 years, 5–9 years, 10–14 years) in the light of thedifferent amounts of time spent in the home and theirability to satisfactorily perform PEFR measurements.Analyses were also conducted for children aged 5–14 years. PEFR measurements were dichotomized intolow and high categories, with thresholds based onapproximate age-specific mean values of all studyparticipants. Air pollutant measurements were dichot-omized using thresholds based approximately on themedian measurement: 768 lg/m3 for NO2, 0.34 ppmfor CO and 1020 lg/m3 for PM10. The selection ofrelevant activities of daily living was undertaken on thebasis of exploratory data analysis. Various dichotomiesof the variables �time spent by a cooking place� and�time spent by a fire� were considered (<1 h, <2 h forchildren; <4 h for adults). Adjusted odds ratios forlow PEFR were calculated using binary logisticregression with potential explanatory variables com-prising the selected activities of daily living and thethree measured air pollutants.

Results

Summary statistics

Of the 199 houses in which measurements were made,approximately 90% of the data (181 houses) wasanalysed; exclusions were because of data missing atrandom and other random problems, including inabil-ity to unambiguously match the tube or filter with thecorresponding data sheet. Mean indoor PM10 and NO2

concentrations were significantly higher in Vientiane

(PM10 = 1275 ± 98 lg/m3, 95% CI 1081–1469 lg/m3; NO2 = 1210 ± 94 lg/m3, 95% CI 1023–1396 lg/m3) than in Bolikhamxay (PM10 = 1183 ± 99 lg/m3,95% CI 984–1382 lg/m3; NO2 = 561 ± 45 lg/m3,95% CI 471–651 lg/m3), but CO concentrations weresignificantly higher in Bolikhamxay (CO = 0.430 ±0.032 ppm, 95% CI 0.367–0.494 ppm compared toCO = 0.490 ± 0.059 ppm, 95% CI 0.372–0.609 ppmrespectively). A summary of the proportion of subjectsexceeding the nominated thresholds of each indoor airpollutant is given in Figure 2.Summaries of the health outcomes that were

included in the analysis of the association betweenindoor air pollutant measurements and questionnaire-based respiratory health are provided in Tables 1–3,respectively. The selection of relevant daily activitieswas undertaken prior to the study design, based oncollaborator input, as well as published literature, andwas subsequently confirmed on the basis of exploratorydata analysis. They comprised of seven potentialexplanatory variables for children aged 1–14 years(Table 4) and eight variables for adults (Table 5).Tables 4 and 5 also show the sample sizes (frequency,percentage) for subjects with both lung function andpollutant measurements.A summary of the PEFR measurements for the study

subjects included in the analysis is provided inFigure 3. The figure also shows the approximate age-specific mean values of all study participants, on whichthe dichotomy into high and low values was based.

Association between indoor air pollutants and questionnaire-basedresponses

There was a strong and consistent association betweenNO2 and CO for almost all health outcomes for bothwomen and children. Tables 6–8 provide a summary of

0

20

40

60

80

100

120

Low High Low High Low High

NO2 CO PM10

Indoor Pollutant

Freq

uenc

y

1–4 yrs 5–9 yrs 10–14 yrs

Fig. 2 Number of subjects with measurements below and abovethe nominated thresholds of each indoor air pollutant. Mea-surements below the threshold are denoted as �low� and thoseabove the threshold as �high�. Thresholds for NO2, CO andPM10 were 0.40 mg/m3, 0.34 ppm and 1.02 mg/m3, respectively

Mengersen et al.

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odds ratios and 95% confidence intervals for thoseoutcomes that were statistically significant at the 10%level. With a few exceptions, these results indicatepositive associations between raised pollutant levelsand increased respiratory illness.Children aged 1–4 years in dwellings with higher

levels of CO and NO2 were more than twice as likelyto suffer from stinging or watering eyes with orwithout pus, not because of colds in the last year. Thepositive odds ratios ranged between 1.31 and 3.31 forNO2 and 1.29 and 2.37 for CO. PM10 was onlyassociated with pneumonia in the past year. Thesepositive associations largely persisted after adjustmentfor age and gender of the children. The adjustmentsalso accounted for the apparent protective effect ofincreased NO2 for cold and fever, and of CO for coldin the past 2 weeks.

Children aged 5–14 years had significantly increasedodds ratios associated with NO2 for the followinghealth outcomes: difficulty in breathing, cough notcaused by colds with and without faster breathing,chest whistling caused by physical movement or withno physical movement not because of colds, waking inthe night because of wheezing and coughing, notbecause of colds, runny nose not because of colds, eyesthat sting and water or are itchy, itchy eyes with orwithout pus not because of colds, itchy rash or eczema,middle ear infection and pneumonia. The correspond-ing odds ratios ranged from 1.64 to 2.79 for symptomsin the past month, and 1.34 to 6.96 for symptoms in thepast year. With the exception of itchy rash or eczema,

Table 1 Summary of questionnaire-based respiratory health outcomes in children aged1–4 yearsb

Questiona Response In past 2 weeks In past month

Ill with a cold No 174 (36.3%) 125 (26.3%)Yes 305 (63.7%) 350 (73.7%)

Ill with a fever No 254 (53.1%) 191 (40.0%)Yes 224 (46.9%) 287 (60.0%)

Ill with a cough No 196 (41.7%) 144 (30.6%)Yes 274 (58.3%) 327 (69.4%)

Wake in the night with coughor wheezing not caused bycolds

No 206 (58.0%) 235 (51.8%)Yes 149 (42.0%) 219 (48.2%)

Runny nose not caused bycolds

No 285 (61.0%) 264 (56.1%)Yes 182 (39.0%) 207 (43.9%)

Breathing difficulty at anytime

No 345 (75.7%) 310 (67.0%)Yes 111 (24.3%) 153 (33.0%)

Breathing difficulty, notcaused by colds or otherillness

No 66 (62.9%) 53 (51.5%)Yes 39 (37.1%) 50 (48.5%)

Stinging or watering eyeswithout pus, not caused by

colds

No 404 (85.8%) 390 (82.5%)Yes 67 (14.2%) 83 (17.5%)

Stinging or watering eyeswith pus, not caused bycolds

No 436 (92.6%) 424 (89.5%)Yes 35 (7.4%) 50 (10.5%)

Itchy rash or eczema No 398 (83.8%) 381 (80.4%)Yes 77 (16.2%) 93 (19.6%)

Ever diagnosed with bronchitis No 286 (61.4%)Yes 180 (38.6%)

Ever had a tonsillectomy No 465 (98.7%)Yes 6 (1.3%)

Diagnosed with a middle earinfection in the last

12 months

No 453 (94.6%)Yes 26 (5.4%)

Ever diagnosed with a middleear infection

No 448 (93.9%)Yes 29 (6.1%)

Diagnosed with pneumonia inthe last 12 months

No 306 (65.5%)Yes 161 (34.5%)

Ever diagnosed withpneumonia

No 310 (65.8%)Yes 161 (34.2%)

aThe above variables represent respiratory symptoms in the last 2 weeks and in the last1 month.bEach dependent variable includes three categories, �No�, �Yes� and �Don�t remember�.Those cases with �Don�t remember� were not included in the respective analysis.

Table 2 Summary of questionnaire-based respiratory health outcomes in children aged5–14 yearsb

Questiona Response In past month In past year

Ill with a cold No 207 (62.2%) 126 (38.0%)Yes 126 (37.8%) 206 (62.0%)

Difficulty in breathing caused bycolds

No 39 (31.7%) 183 (55.8%)Yes 84 (68.3%) 145 (44.2%)

Difficulty in breathing, not causedby colds

No 248 (87.3%) 264 (81.7%)Yes 36 (12.7%) 59 (18.3%)

Morning cough No 226 (68.3%) 178 (53.6%)Yes 105 (31.7%) 154 (46.4%)

Cough not caused by colds, withbreathing faster than usual withshort rapid breaths

No 283 (85.5%) 263 (80.4%)Yes 48 (14.5%) 64 (19.6%)

Cough not caused by colds, withno change in breathing

No 295 (89.7%) 285 (86.6%)Yes 34 (10.3%) 44 (13.4%)

Chest whistling because ofphysical movement

No 290 (94.2%) 287 (92.6%)Yes 18 (5.8%) 23 (7.4%)

Chest whistling with no physicalmovement, not because of colds

No 297 (96.1%) 287 (93.2%)Yes 12 (3.9%) 21 (6.8%)

Waking in the night from wheezingor coughing, not because of colds

No 288 (88.1%) 273 (83.7%)Yes 39 (11.9%) 53 (16.3%)

Runny nose not caused by colds No 272 (82.9%) 266 (80.4%)Yes 56 (17.1%) 65 (19.6%)

Eyes that sting or water, or areitchy

No 301 (92.3%) 302 (91.0%)Yes 25 (7.7%) 30 (9.0%)

Itchy eyes without pus, not causedby colds

No 8 (32.0%) 308 (93.1%)Yes 17 (68.0%) 23 (6.9%)

Itchy eyes with pus, not caused bycolds

No 10 (41.7%) 311 (94.0%)Yes 14 (58.3%) 20 (6.0%)

Itchy rash or eczema No 297 (90.0%) 285 (85.8%)Yes 33 (10.0%) 47 (14.2%)

Headaches No 235 (71.9%) 198 (60.6%)Yes 92 (28.1%) 129 (39.4%)

Ever diagnosed with asthma No 295 (89.4%)Yes 35 (10.6%)

Ever diagnosed with bronchitis No 279 (86.9%)Yes 42 (13.1%)

Ever had a tonsillectomy No 321 (99.1%)Yes 3 (0.9%)

Diagnosed with pneumonia in thelast 12 months

No 306 (93.3%)Yes 22 (6.7%)

Diagnosed with a middle earinfection in the last 12 months

No 305 (92.4%)Yes 25 (7.6%)

aThe above variables represent respiratory symptoms in the last 1 month and in the last12 months.bEach dependent variable includes three categories, �No�, �Yes� and �Don�t remember�.Those cases with �Don�t remember� were not included in the respective analysis.


29

all of these symptoms were also adversely associatedwith CO. These odds ratios were noticeably larger thanthe corresponding values for NO2. Waking in the nightfrom wheezing or coughing not because of colds anditchy rash or eczema were the only outcomes that wassignificantly associated with PM10.Significant adverse associations were also found for

women. Women in dwellings with higher measuredNO2 had more than double the odds of almost all ofthe health outcomes considered. As with the youngchildren, CO was more modestly associated withadverse health outcomes in the past month and thepast 12 months, although the risk was consistent andhighly statistically significant.As expected, the aforementioned effects were

ameliorated by the inclusion of a constant in theregression models. For example, among women,

Table 4 Potential explanatory variables, children aged 1–14 years

Factor Category Codea

Frequency

1–4 years 5–14 years

Sex Male 0 103 (56%) 53 (46%)Female 1 81 (44%) 62 (54%)

Time spent by acooking placeper day

<2 h 0 112 (61%) 80 (70%)More than 2 h 1 72 (39%) 35 (30%)

Time spent bya fire per day

<2 h 0 126 (68%) 85 (74%)More than 2 h 1 58 (32%) 30 (26%)

Amount of dustoutside

Never or Sometimesa lot

0 78 (42%) 53 (46%)

Always a lot 1 106 (58%) 62 (54%)Amount of dust

insideNever or Sometimes

a lot0 91 (49%) 60 (52%)

Always a lot 1 93 (51%) 55 (48%)Do you dry clothes

inside?Never 0 58 (32%) 40 (35%)Sometimes or Often 1 126 (68%) 75 (65%)

Does anyone whocurrently lives inyour house smoketobacco?

No 0 54 (29%) 78 (68%)Yes 1 130 (71%) 37 (32%)

Restricted to children who have a NO2, CO or peak expiratory flow rate recorded.a0 denotes reference category.

Table 3 Summary of questionnaire-based respiratory health outcomes in women aged15+ yearsb

Questiona ResponseIn the pastmonth In the past year

Tightness in the chest No 292 (75.5%) 262 (68.2%)Yes 95 (24.6%) 122 (31.8%)

Morning cough No 295 (77.0%) 237 (61.6%)Yes 88 (23.0%) 148 (38.4%)

Shortness of breath No 291 (76.0%) 253 (66.1%)Yes 92 (24.0%) 130 (33.9%)

Morning phlegm No 293 (76.1%) 252 (65.6%)Yes 92 (23.9%) 132 (34.4%)

Chest whistling because ofphysical movements

No 335 (89.3%) 323 (85.4%)Yes 40 (10.7%) 55 (14.6%)

Chest whistling or wheezing withno physical movement, notbecause of colds

No 344 (91.5%) 328 (88.2%)Yes 32 (8.5%) 44 (11.8%)

Waking in the night from wheezingor coughing, not because of colds

No 317 (83.0%) 299 (77.9%)Yes 65 (17.0%) 85 (22.1%)

Dry cough not caused by colds No 321 (83.4%) 303 (78.7%)Yes 64 (16.6%) 82 (21.3%)

Runny nose not caused by colds No 351 (91.2%) 332 (86.5%)Yes 34 (8.8%) 52 (13.5%)

Itchy eyes, itchy rash or eczema No 335 (86.8%) 315 (81.8%)Yes 51 (13.2%) 70 (18.2%)

Diagnosed with asthma by adoctor or other health worker

No 354 (93.7%)Yes 24 (6.4%)

Diagnosis with bronchitis by adoctor or other health worker

No 351 (92.6%)Yes 28 (7.4%)

Diagnosis with tuberculosis No 374 (96.4%)Yes 14 (3.6%)

Diagnosed with lung cancer No 350 (97.8%)Yes 8 (2.2%)

aThe above variables represent respiratory symptoms in the last 1 month and in the last12 months.bEach dependent variable includes three categories, �No�, �Yes� and �Don�t remember�.Those cases with �Don�t remember� were not included in the respective analysis.

Table 5 Potential explanatory variables, women aged 15+ years

Factor Category Codea Frequency

Time spent by acooking place per day

<4 h 0 67 (48.2%)More than 4 h 1 72 (51.8%)

Time spent bya fire per day

<4 h 0 47 (33.8%)More than 4 h 1 92 (66.2%)

Amount of dustoutside

Never or Sometimes a lot 0 65 (47.5%)Always a lot 1 72 (52.5%)

Amount of dustinside

Never or Sometimes a lot 0 72 (52.5%)Always a lot 1 65 (47.5%)

Do you dry clothesinside?

Never 0 38 (27.8%)Sometimes or Often 1 99 (72.2%)

Does anyone whocurrently lives inyour house smoketobacco?

No 0 97 (70.8%)Yes 1 40 (29.2%)

Do you personallysmoke?

Yes, former or current 1 12 (8.6%)No 0 127 (91.4%)

Are you exposed toother people�ssmoke in the home?

Often 1 52 (37.4%)Sometimes or Never 0 87 (62.6%)

Restricted to women who have a NO2, CO or peak expiratory flow rate recorded.a0 denotes reference category.

0

50

100

150

200

250

300

350

400

1 yr 2 yr 3 yr 4 yr 5–9

yrs

10–14

yrs

20–29

yrs

30–39

yrs

40–49

yrs

50+

yrs

PEFR

Fig. 3 Mean peak expiratory flow rate (PEFR) measurements±1 s.d. for specified age groups. Threshold PEFR measure-ments were chosen to be 25, 75, 85, 115, 155, 215, 265, 255, 235and 195, respectively

Mengersen et al.

30

positive associations persisted between NO2 andcough, PM10 and cough and asthma, and CO andchest whistling with and without physical movements,asthma, tuberculosis and lung cancer.

Association between indoor air pollutants and lung functionmeasurements

Among children aged 1–4 years, of the ten potentialexplanatory variables, only the concentration of PM10

was statistically significantly associated with lowerPEFR (P = 0.026). The corresponding odds ratiowas 2.04 (95% CI 1.09–3.84), indicating a doublingof the risk of below average PEFR in children residingin households with PM10 above 1020 lg/m3. Morethan half of the children in the study (52%) lived indwellings in which the recorded concentrations ofPM10 were at least this high (Table 1).No significant associations with lower than average

PEFR were observed for children aged 5–9 years and10–14 years. However, the analysis of children aged 5–14 years revealed significantly increased odds ratiosassociated with >2 h per day by a fire (OR 7.24, 95%CI 1.35–38.84).Among women aged 15+ years, of the 11 potential

explanatory variables, only higher concentrations ofNO2 and CO were significantly associated with lowerPEFR (P = 0.001 and P = 0.029, respectively). Theodds ratio for CO was 2.29 (95% CI 1.09–4.84),representing more than double the risk of lower thanaverage PEFR among women residing in householdswith more than 0.34 ppm. More than half of thewomen in the study (52%) lived in dwellings in which

the recorded concentrations of CO were at least thishigh (Table 3). Conversely, the odds ratio for NO2 was0.232 (95% CI 0.099–0.544).Among women, there was a nonsignificant but

suggestive (P = 0.098) increase in risk of lower thanaverage PEFR associated with drying clothes inside(OR = 1.91, 95% CI 0.89–4.13). A similar associationwas observed among children aged 1–4 years in alogistic regression analysis using the same variables asin Table 1 but with the time spent by a fire categorizedby more or <1 h (P = 0.062, OR = 1.89, 95% CI0.97–3.71). In this analysis, PM10 persisted in being theonly other statistically significant variable associatedwith reduced PEFR (P = 0.019, OR = 2.11, 95% CI1.13–3.96).Among the children aged 1–4 years, there was a

nonsignificant but suggestive (P = 0.098) reduction inrisk of lower than average PEFR associated with thepresence of a smoker in the household (OR = 0.58,95% CI 0.31–1.11). In contrast, raised but not signif-icant odds ratios for household smoking were observedamong older children and women (OR = 2.005, 95%CI 0.67–6.03 for children aged 5–9 years; OR = 1.94,95% CI 0.38–9.93 for children aged 10–14 years;OR = 1.77, 95% CI 0.73–4.30 for women). The reasonwhy respiratory symptoms increased with age forchildren is not clear and further, targeted investigationsare required to address this point.

Discussion

The global burden of death and diseases associatedwith acute respiratory infections, especially in

Table 6 Statistically significanta odds ratios and 95% confidence intervals for questionnaire-based respiratory outcomes in children aged 1–4 years

Question Pollutant

In the last 2 weeks In the last month

OR (95% CI) P-value OR (95% CI) P-value

A cold at any time CO 0.76 (0.59, 0.98) 0.0354NO2 0.67 (0.49, 0.91) 0.0097

Ill with a fever at any time NO2 0.72 (0.54, 0.95) 0.0215 1.31 (0.99, 1.74) 0.0596Waking in the night with wheezing or cough not caused by colds CO 1.31 (1.00, 1.73) 0.0535

NO2 0.75 (0.53, 1.05) 0.0887Runny nose not caused by colds CO 1.33 (1.04, 1.70) 0.0234

NO2 1.63 (1.19, 2.23) 0.0025Suffer from difficulty in breathing at any time CO 1.47 (1.11, 1.93) 0.0071 1.29 (0.99, 1.68) 0.0602

NO2 1.34 (0.98, 1.83) 0.0706 1.86 (1.33, 2.60) 0.0003Stinging or watering eyes without pus, not caused by colds CO 1.74 (1.25, 2.42) 0.0011 2.15 (1.43, 3.24) 0.0003

NO2 1.98 (1.38, 2.85) 0.0002 2.40 (1.56, 3.68) 0.0001Stinging or watering eyes with pus, not caused by colds CO 2.96 (1.77, 4.96) 0.0000 2.37 (1.50, 3.74) 0.0002

NO2 2.58 (1.62, 4.13) 0.0001 3.31 (2.00, 5.48) 0.0000Itchy rash or eczema CO 1.41 (1.06, 1.88) 0.0198 1.49 (1.10, 2.01) 0.0089

NO2 1.84 (1.31, 2.58) 0.0004 1.96 (1.37, 2.79) 0.0002Bronchitis* CO 0.68 (0.49, 0.95) 0.0250

NO2 0.54 (0.34, 0.84) 0.0071Pneumonia* NO2 1.46 (1.09, 1.95) 0.0105

PM10 1.42 (0.99, 2.02) 0.0540

*The health outcomes of bronchitis and pneumonia were diagnosed in the past year.aP < 0.10.


31

developing countries, is well acknowledged (WHO,2002). This study confirms the role of indoor airpollution in this burden of disease in one of the world�sleast developed countries, Lao PDR.Unlike most studies that attempt to quantify this

burden, the analyses reported here are based on directmeasurements of air pollutants in dwellings included inthe study, and two measures of respiratory health ofresidents of these dwellings: self-reported symptomsobtained by questionnaire, and direct lung functionmeasurements taken by trained Ministry of Healthstaff. The measurements conducted within the 12- hperiod (one day) were assumed to be representative oftypical living indoor air concentrations. While thequestionnaire itself did not include questions to checkthis assumption, the interviewers were instructed to askwhether any unusual activities or occurrences tookplace, which could have had an impact on air quality.There were also asked to assess the situation them-selves and report any observation in the first part of thequestionnaire (Part A: Interviewer Information). Thecomments provided by the interviewers were reviewed,and based on their comments the conditions of all

houses during the measurements were consideredrepresentative.The results of the questionnaire study confirm

statistically significantly increased odds ratios for manyreported respiratory symptoms, associated variouslywith each of NO2, CO and PM10. While some adverseassociations were evident for children aged 1–4 years,the range and magnitude of the associations increasedfor children aged 5–14 years and for women. Theassociations were strongest for NO2 and more modestfor CO among children aged 1–4 years and women;this pattern was reversed for children aged 5–14 years.Associations with PM10 were limited in children andnot significant for any of the reported respiratoryoutcomes in women. Except for wood burning, thedifference between PM10 and CO might result fromadditional PM10 emission sources (i.e. dust re-suspen-sion and smoking) that existed in the study area. Tobetter target PM emissions from wood smoke in thefuture, and to distinguish them from resuspended dust,it would be more appropriate to measure particlenumber concentration, as the majority of particlesemitted from wood burning are in the submicrometer

Table 7 Statistically significant* odds ratios and 95% confidence intervals for questionnaire-based respiratory outcomes in children aged 5–14 years

Question Pollutant

In the last month In the last year


Difficulty in breathing, caused by colds NO2 0.39 (0.18, 0.85) 0.0184Difficulty in breathing, not caused by colds CO 7.70 (2.74, 21.6) 0.0001 1.97 (1.16, 3.35) 0.0119

NO2 1.55 (0.98, 2.44) 0.0619Morning cough CO 1.45 (1.00, 2.10) 0.0498Cough not caused by colds, with breathing faster

than usual and with short rapid breathsCO 3.45 (1.74, 6.85) 0.0004 5.04 (2.20, 11.5) 0.0001NO2 1.34 (0.81, 2.23)

Cough not caused by colds, no change in breathing CO 6.21 (2.45, 15.7) 0.0001 13.6 (3.84, 48.1) 0.0001NO2 1.64 (0.93, 2.87) 0.0859 1.83 (0.97, 3.45) 0.0636

Chest whistling because of physical movement CO 3.40 (1.48, 7.81) 0.0040 7.79 (2.56, 23.7) 0.0003NO2 2.36 (1.26, 4.41) 0.0073 1.77 (0.95, 3.29) 0.0722

Chest whistling with no physical movement, not because of colds CO 15.2 (3.39, 68.1) 0.0004 4.17 (1.65, 10.6) 0.0026NO2 2.79 (1.21, 6.46) 0.0165 2.58 (1.32, 5.05) 0.0056PM10

Waking in the night from wheezing or coughing, not because of colds CO 2.98 (1.52, 5.87) 0.0015 4.45 (1.91, 10.4) 0.0006NO2 2.06 (1.16, 3.66) 0.0136PM10 1.79 (1.02, 3.16) 0.0426

Runny nose not caused by colds CO 3.09 (1.61, 5.91) 0.0007 3.06 (1.55, 6.03) 0.0012NO2 1.57 (0.96, 2.55) 0.0723

Eyes that sting or water, or are itchy CO 3.81 (1.72, 8.44) 0.0010 18.6 (4.40, 78.7) 0.0001NO2 2.03 (1.16, 3.57) 0.0135 2.17 (1.07, 4.41) 0.0317

Itchy eyes without pus, not caused by colds CO 10.5 (2.94, 37.3) 0.0003NO2 4.30 (1.75, 10.6) 0.0015

Itchy eyes with pus, not caused by colds CO 7.38 (2.40, 22.6) 0.0005NO2 4.06 (1.76, 9.37) 0.0010

Itchy rash or eczema CO 3.32 (1.53, 7.18) 0.0024NO2 2.42 (1.31, 4.45) 0.0047 2.26 (1.40, 3.66) 0.0009PM10 1.67 (1.00, 2.77) 0.0493

Headaches CO 1.49 (1.00, 2.23) 0.0525Diagnosed with middle ear infection CO 24.9 (4.43, 140) 0.0003

NO2 6.96 (1.92, 25.2) 0.0032Diagnosed with pneumonia CO 16.3 (4.01, 65.9) 0.0001

NO2 2.33 (1.14, 4.76) 0.0206

*P < 0.10.

Mengersen et al.

32

range (although this would still not allow researchersto distinguish between wood and tobacco smoke, as thesize of particles originating from these two sources aresimilar). However, like many other studies conductedin developing courtiers, the high cost of particlecounters and issues with access to power (there wasno electricity in many of the houses, and the particlecounters available could not operate on a battery for12 h) meant that this was not possible in this study.The questionnaire study also identified a significant

association (P < 0.05) between reduced PEFR andmore than 2 h per day by a fire among children aged 5–14 years. In the analysis of older children (5–14 years),the odds ratio associated with more than 2 h spent by afire was significantly raised (P = 0.021, OR = 7.24,95% CI 1.35–38.84) and when the three pollutantswere omitted from the model, positive associationsbetween more than 2 h spent by a fire and reducedPEFR were observed among children aged 1–4 years(P = 0.063, OR = 1.64, 95% CI 0.97–2.77), childrenaged 5–9 years (P = 0.034, OR = 1.60, 95% CI 1.08–8.03) and children aged 5–14 years (P = 0.006,OR = 3.42, 95% CI 1.43–8.18).Mixed results were obtained for analysis of the direct

lung function measurements. After adjusting the PEFRthreshold for age and accounting for activities of dailyliving, higher concentrations of PM10 and CO were

found to be significantly associated with lower thanaverage lung function among children 1–4 years andwomen 15+ years, respectively. On the contrary,higher concentrations of NO2 were found to besignificantly inversely associated with lower PEFRamong the women; this result is not immediatelyinterpretable in the light of the other positive associ-ations observed in this study, but may be in partattributed to the strong positive correlation betweenNO2 and CO and is supported in part by similar resultsand commentary in some other studies (Koistinenet al., 2008; Beckett et al., 2006).Although the lung function study was conducted by

trained staff, many of whom were medical doctors, it isacknowledged that these results should be consideredin the light of the limitations of the PEFR measureitself and the practical issues of administration of thestudy. Despite these constraints, however, the studyprovided a unique opportunity to gain insight into theassociation between direct measures of both lungfunction and indoor air pollutants and gave positivesupport for the corresponding indirect associationsobtained through the questionnaire study.The moderate nature of the observed risks in the

questionnaire study, as indicated by the size andsignificance of the corresponding odds ratios, is in linewith the published literature (Bruce et al., 2000; Smith

Table 8 Statistically significant* odds ratios and 95% confidence intervals for questionnaire-based respiratory outcomes in women aged 15+ years

Question Pollutant

In the last month In the last year


Tightness in the chest CO 1.55 (1.12, 2.14) 0.0078 1.28 (0.96, 1.70) 0.0883NO2 1.55 (1.06, 2.28) 0.0249 1.69 (1.16, 2.46) 0.0060

Morning cough CO 1.44 (1.04, 2.01) 0.0304NO2 2.42 (1.54, 3.81) 0.0001

Shortness of breath CO 1.40 (1.03, 1.92) 0.0341 1.35 (1.01, 1.81) 0.0439NO2 2.04 (1.35, 3.10) 0.0008 1.64 (1.12, 2.39) 0.0109

Morning phlegm NO2 1.74 (1.20, 2.54) 0.0038 1.38 (0.98, 1.95) 0.0679Chest whistling because of physical movements CO 1.93 (1.25, 2.98) 0.0032 2.04 (1.30, 3.19) 0.0019

NO2 3.20 (1.80, 5.70) 0.0001 2.72 (1.60, 4.64) 0.0002Chest whistling with no physical movement, not because of colds CO 2.76 (1.54, 4.95) 0.0006 2.21 (1.35, 3.63) 0.0017

NO2 4.14 (2.04, 8.42) 0.0001 3.48 (1.87, 6.50) 0.0001Waking in the night from wheezing or coughing, not caused by colds CO 1.66 (1.16, 2.38) 0.0061 1.35 (1.00, 1.83) 0.0503

NO2 2.07 (1.32, 3.24) 0.0015 1.94 (1.30, 2.91) 0.0013Dry cough not caused by colds CO 1.84 (1.25, 2.72) 0.0019 1.52 (1.09, 2.13) 0.0144

NO2 1.94 (1.24, 3.03) 0.0035 2.22 (1.43, 3.45) 0.0004Runny nose not caused by colds CO 2.65 (1.58, 4.44) 0.0002 2.16 (1.39, 3.36) 0.0007

NO2 2.07 (1.24, 3.43) 0.0050 2.07 (1.29, 3.33) 0.0026Itchy eyes, itchy rash or eczema CO 1.79 (1.23, 2.60) 0.0022 1.53 (1.10, 2.14) 0.0118

NO2 1.88 (1.23, 2.89) 0.0038 1.96 (1.29, 2.97) 0.0017Diagnosed with asthma CO 2.69 (1.53, 4.72) 0.0006

NO2 3.60 (1.90, 6.82) 0.0001Ever diagnosed with bronchitis CO 1.66 (1.15, 2.40) 0.0070

NO2 2.45 (1.53, 3.93) 0.0002Diagnosed with tuberculosis CO 5.20 (2.35, 11.5) 0.0000

NO2 2.79 (1.48, 5.26) 0.0014Diagnosed with lung cancer CO 6.02 (2.34, 15.5) 0.0002

NO2 3.88 (1.79, 8.43) 0.0006

*P < 0.10.


33

and Mehta, 2003; Ezzati, 2005; Smith et al., 2005;Desai et al., 2004; Kara et al., 2003; Ozbay et al.,2001). Appropriate adjustment for confounding factorsin epidemiological studies such as the one reported hereis acknowledged to be problematic (Schwartz, 1994).Although controlling for age (and gender whererelevant) is almost universally agreed, the inclusion ofother factors and competing risks in a multivariatemodel can substantially change the observed risksassociated with particular exposures (Bruce et al.,2000). The implication of this problem for this studyis that all reported estimates of odds ratios must beconsidered in the light of the other variables in themodel.The WHO Child Health Epidemiology Reference

Group has provided methodological guidelines for thedesign, conduct and reporting of epidemiologicalstudies of acute lower respiratory infections in under-5s in developing countries (Lanata et al., 2004). Mostof these apply directly, or can be extended to thereporting of respiratory illness in women in thesecommunities. The strength of this study is that it hasaccess to almost all of the study setting characteristics

and has adhered to almost all of the study designconsiderations that were listed by the Reference Groupas determinants of study quality. Although it suffersfrom drawbacks common to all studies of this type, itscontribution to the accumulation of evidence willprovide more reliable estimates of risk and a moreinformed basis for decision-making by concernedgovernments and communities.

Acknowledgements

This study was funded by the World Health Organi-sation (WHO) with financial and resource supportfrom ILAQH, QUT. We thank Dr Ogawa Hisahsifrom the WHO Western Pacific Regional Office for hisvision and support for this study. Involvement of theresearch staff at the Ministry of Health, Lao PDR forconducting the measurements and survey is greatlyappreciated. Advice by Eva Rehfuess from WHO,Public Health and Environment, Geneva and MrsKirstie Jagoe at the Department of Public Health,University of Liverpool, in relation to the study designand questionnaire matters is greatly appreciated.

References

Beckett, W.S., Gent, J.F., Naeher, L.P.,Belanger, K., Triche, E.W., Bracken,M.B. and Leaderer, B.P. (2006) Peakexpiratory flow rate variability is notaffected by home combustion sources in agroup of non-smoking women, Arch.Environ. Occup. Health, 61, 176–182.

Bruce, N., Perez-Padilla, R. and Albalak, R.(2000) Indoor air pollution in developingcountries: a major environmental andpublic health challenge, Bull. WorldHealth Organ., 78, 1078–1092.

Daisey, J.M., Spengler, J.D. and Kaarakka,P. (1989) A comparison of the organicchemical composition of indoor aerosolsduring woodburning and non-wood-burning periods, Environ. Int., 15, 435–442.

Dales, R., Liu, L., Wheeler, A.J. and Gilbert,N.L. (2008) Quality of indoor residentialair and health, Can. Med. Assoc. J., 179,147–152.

Desai, M.A., Mehta, S. and Smith, K.R.(2004) Indoor Smoke from Solid Fuels:Assessing the Environmental Burden ofDisease at National and Local Levels., inEnvironmental Burden of Disease SeriesNo. 4. Geneva, World Health Organiza-tion (Editor).

Dherani, M., Pope, D., Mascarenhas, M.,Smith, K.R., Weber, M. and Bruce, N.(2008) Indoor pollution from unprocessedsolid fuel use and pneumonia risk inchildren aged under five years: a system-atic review and meta-analysis, Bull. WorldHealth Organ., 86, 390–398.

Diaz, E., Bruce, N., Pope, D., Lie, R.T.,Diaz, A., Arana, B., Smith, K.R. andSmith-Siversten, T. (2007) Lung functionand symptoms among indigenous Mayanwomen exposed to high levels of indoorair pollution, Int. J. Tuberc. Lung Dis., 11,1372–1379.

Dionisio, K.L., Howie, S., Fornance, K.M.,Chimah, O., Adegbola, R.A. and Ezzati,M. (2008) Measuring the exposure ofinfants and children to indoor air pollu-tion from biomass fuels in The Gambia,Indoor Air, 18, 317–327.

Epton, M.J., Dawson, R.D., Brooks, W.M.,Kingham, S., Aberkane, T., Cavangh,J.E., Frampton, C.M., Hewitt, T., Cook,J.M., McLeod, S., McCartin, F.,Trought, K. and Brown, L. (2008) Theeffect of ambient air pollution on respi-ratory health of school children: a panelstudy, Environ. Health, 7, 1–11.

Ezzati, M. (2005) Indoor air pollution andhealth in developing countries, Lancet,366, 104–106.

Fischer, S. and Koshland, C.P. (2007) Dailyand peak 1 h indoor air pollution anddriving factors in a rural Chinese village,Environ. Sci. Technol., 41, 3121–3126.

Franklin, P. (2007) Indoor air quality andrespiratory health for children, Paediatr.Respir. Rev., 8, 281–286.

Grigg, J. (2007) Effect of biomass smoke onpulmonary host defence mechanisms,Paediatr. Respir. Rev., 8, 287–291.

Kara, M., Bulut, S., Tas, F., Akkurt, I. andSeyfikli, Z. (2003) Evaluation of pulmo-

nary changes due to biomass fuels usinghigh-resolution computed tomography,Eur. Radiol., 13, 2372–2377.

Koistinen, K., Kotzias, D., Kephalopolous,S., Schlitt, C., Carrer, P., Jantunen, M.,Kirchner, S., McLaughlin, J., Molhave,L., Fernandes, E.O. and Seifert, B. (2008)The INDEX Project: Executive summaryof a European Union project on indoorair pollutants, Allergy, 63, 810–819.

Kumar, R., Nagar, J.K., Kumar, H.,Kushwah, A.S., Meena, M., Kumar, P.,Raj, N., Singhal, M.K. and Gaur, S.N.(2007) Associations of indoor and out-door pollutant level with respiratoryproblems among children in an industrialarea of Delhi, India, Arch. Environ.Occup. Health, 62, 75–80.

Lanata, C.F., Rudan, I., Boschi-Pinto, C.,Tomaskovic, L., Cherian, T., Weber, M.and Campbell, H. (2004) Methodologi-cal and quality issues in epidemiologicalstudies of acute lower respiratoryinfections in children in developingcountries, Int. J. Epidemiol., 33, 1362–1372.

Liu, S., Zhou, Y., Wang, X., Wang, D., Lu,J., Zheng, J., Zhong, N. and Ran, P.(2007) Biomass fuels are the probable riskfactor for chronic obstructive respiratorydisease in rural South China, Thorax, 62,889–897.

Liu, Y., Lee, K., Perez-Padilla, R., Hudson,N.L. and Mannino, D.M. (2008) Outdoorand indoor air pollution and COPD-related diseases in high- and low-income

Mengersen et al.

34

countries, Int. J. Tuberc. Lung Dis., 12,115–127.

Nazaroff, W.W. (2008) Inhalation intakefraction of pollutants from episodic in-door emissions, Build. Environ., 43, 269–277.

Oanh, N.T.K., Reutergardh, L.B. and Dung,N.T. (1999) Emission of polycyclic aro-matic hydrocarbons and particulate mat-ter from domestic combustion of selectedfuels, Environ. Sci. Technol., 33, 2703–2709.

Ozbay, B., Uzun, K., Arslan, H. and Zehir, I.(2001) Functional and radiological impair-ment in women highly exposed to indoorbiomass fuels,Respirology, 6, 255–258.

Rinne, S.T., Rodas, E.J., Rinne, M.L.,Simpson, J.M. and Glickman, L.T. (2007)Use of biomass fuel is associated withinfant mortality and child health in trendanalysis, Am. J. Trop. Med. Hyg., 76,585–591.

Rudan, I., Boschi-Pinto, C., Biloglav, Z.,Mulholland, K. and Campbell, H. (2008)

Epidemiology and eitology of childhoodpneumonia, Bull. World Health Organ.,86, 408–416.

Rumchev, K., Spickett, J.T., Brown, H.L.and Mkhweli, B. (2007) Indoor air pol-lution from biomass combustion andrespiratory symptoms of women andchildren in a Zimbabwean village, IndoorAir, 17, 468–474.

Schwartz, J. (1994) Air pollution and dailymortality: a review and meta analysis,Environ. Res., 64, 36–52.

Smith, K.R. and Mehta, S. (2003) The bur-den of disease from indoor air pollution indeveloping countries: comparison of esti-mates, Int. J. Hyg. Environ. Health, 206,279–289.

Smith, K.R., Mehta, S. and Maeusezahl-Feuz, M. (2005) Indoor Air PollutionFrom Household Use of Solid Fuels,in Environmental and occupationalrisk factors. Geneva, WorldHealth Organization (Editor), 1435–1494.

Tuckett, C.J., Holmes, P. and Harrison,P.T.C. (1998) Airborne particles in thehome, J. Aerosol Sci., 29(S1), 293–294.

WHO (2001) World Health Report. Geneva,World Health Organisation.

WHO (2002) World Health Report: ReducingRisks, Promoting Healthy Life. Geneva,World Health Organisation.

Wigle, D.T., Arbuckle, T.E., Walker, M.,Wade, M.G., Liu, S. and Krewski, D.(2007) Environmental hazards: Evidencefor effects on child health, J. Toxicol.Environ. Health, Part B, 10, 3–39.

Wornat, M.J., Ledesma, E.B., Sandrowitz,A.K., Roth, M.J., Dawsey, S.M., Qiao,Y.-L. and Chen, W. (2001) Polycyclicaromatic hydrocarbons identified in sootextracts from domestic goal burningstoves of Henan Province, China, Envi-ron. Sci. Techn., 35, 1943–1952.

Zhang, J.F. and Smith, K.R. (1999) Emis-sions of carbonyl compounds from vari-ous cookstoves in China, Environ. Sci.Technol., 33, 2311–2320.


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