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Household Air Pollution and Under-Five Mortality in Bangladesh (2004–2011)

Friday, 29th of April 2016

Int J Environ Res Public Health. 2015 Oct; 12(10): 12847–12862.

Household Air Pollution and Under-Five Mortality in Bangladesh (2004–2011)

Sabrina Naz,^1,* Andrew Page,¹ and Kingsley Emwinyore Agho²

Gary Adamkiewicz, Academic Editor

Excerpt below; full text is at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4627003/

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Household air pollution (HAP) is one of the leading causes of respiratory illness and deaths among children under five years in Bangladesh. This study investigates the association between HAP from cooking fuel and under-five mortality using Bangladesh Demographic and Health Survey (BDHS) datasets over the period 2004–2011 (n = 18,308 children), and the extent to which this association differed by environmental and behavioral factors affecting level of exposure. The association between HAP and neonatal (age between 0–28 days), infant (age between 0 and 11 months) and under–five (age between 0 and 59 months) mortality was examined using multilevel logistic regression models. HAP was not strongly associated with overall neonatal (OR = 1.49, 95% CI = 1.01–2.22, p = 0.043), infant (OR = 1.27, 95% CI = 0.91–1.77, p = 0.157) or under-five mortality (OR = 1.14, 95% CI = 0.83–1.55, p = 0.422) in the context of overall decreasing trends in under-five mortality. The association was stronger for households with an indoor kitchen using polluting fuels, and in women who had never breastfed. Reductions in exposure to pollution from cooking fuel, given it is a ubiquitous and modifiable risk factor, can result in further declines in under-five mortality with household design and behavioural interventions.

Keywords: Household air pollution, indoor air pollution, under-five mortality, cooking fuels, Bangladesh

Household air pollution (HAP) from cooking fuel is a substantial cause of respiratory illness and death and remains a major public health concern in the developing world [1,2]. Globally, more than three billion people depend on solid fuels (wood, animal dung, crop residues, charcoal and coal) for cooking and heating and, in the case of rural populations, approximately 90% households use biomass fuels as their primary source of domestic energy [3,4,5]. Polluted indoor air is associated with a range of health damaging pollutants such as fine particles, carbon monoxide (CO₂), nitrogen oxides (NO₂), sulphur dioxide (SO₂), benzene, butadiene, formaldehyde, polyaromatic hydro-carbons and a number of other chemicals [6,7].

The poorest populations of the world are most vulnerable to the effects of household air pollution (HAP), with approximately 4.3 million deaths worldwide has been attributable to HAP in 2012 [8]. HAP has a disproportionately adverse effect on the health of women and children under five years of age, particularly acute respiratory infections (ARI) [4,9] as women are predominantly responsible for cooking in developing societies which usually occurs indoors with fuel burnt in open, poor functioning stoves [4,10]. In addition, children are more vulnerable to air pollution than adults because of their higher oxygen consumption rate for which they inhale more pollutants and also for the fact that their airways are narrower which results more irritation for greater airway obstruction [11,12]. However, young children are at greater risk of exposure from cooking fuel than older children as they spend more time indoors [2,10,13].

Bangladesh is a developing and overpopulated low land country located in South Asia. Nearly, 31% of people in peri-urban and rural areas live in poverty [14]. Approximately 86% of the population still rely primarily on solid fuels as a domestic source of energy, particularly in rural households [14]. Around 3.6% of the total burden of disease in the country has been attributable to HAP and 21% of deaths among children <5 years are associated with ARI [15,16]. Over the past decades, under-five mortality in Bangladesh has dropped by 72% from 144 deaths per 1,000 live births in 1990 to 41 in 2012 [17]. Despite this, pneumonia is still the leading single cause of under-five deaths in Bangladesh, accounting for one-fifth of all deaths [14].

Previous studies in Bangladesh have examined the effects of HAP on respiratory diseases among young children, but have been limited to surveys of limited geographic areas, or hospital based data sources for specific regional populations [18,19,20,21,22,23]. To date, no study for Bangladesh has examined the effect of HAP on nationally representative under-five mortality, and no studies have examined changes over time or investigated the role of environmental and behavioral factors that might affect the level of exposure to HAP (for example, place of residence, breastfeeding status and location of kitchen). Accordingly, the objective of this study was to investigate trends in the association between HAP and under-five mortality, and assess how this is affected by key environmental and behavioral factors using nationally representative data over the period 2004–2011.

2.1. Data Sources

The data in this study were extracted from the most recent Bangladesh Demographic and Health Survey (BDHS) datasets for the years 2004, 2007 and 2011. The BDHS are nationally representative household surveys conducted every three to four years since 1993 under the authority of the National Institute of Population Research and Training (NIPORT) of the Ministry of Health and Family Welfare, implemented by Mitra and Associates in Dhaka (Bangladesh) with technical assistance from ICF international of Calverton, Maryland, USA, as a part of its Demographic and Health Surveys Program [14,24,25]. The BDHS data were collected by interviewing ever-married women (aged 10–49 years) and men (aged 15–54 years) using a stratified sample of households based on a two-stage cluster design [14,24,25]. A total of 40,439 ever-married women of reproductive age (14,320 from urban and 26,119 from rural areas) were included in the three datasets with a response rate of 98.3% in women across the three datasets (2004, 2007 and 2011). This study was based on information relating to 18,308 singleton live-born children, of whom 923 died in the 5-years prior to the survey. An index period of five years was to minimize recall bias of child birth and death information self-reported by the mother. (Descriptive characteristics of participating women are provided in aTable S1).

2.1.1. Under-Five Mortality

The analysis was carried out for three age groups: neonatal, infant and under-five mortality, using the following definitions:

(1) Neonatal mortality: The number of deaths during the first 28 days of life (0–28 days). Defined as, Number of neonatal deaths/Total number of live births

(2) Infant mortality: The number of deaths during the first year of life (0–11 months). Defined as, Number of infant deaths/Total number of live births

(3) Under-five mortality: The number of deaths before the fifth birthday (0–59 months). Defined as, Number of under-five deaths/Total number of live births

The outcome variables were considered dichotomous for the analysis, where “age at death” was either yes (=1), denoting death occurred during any of these three periods of age, or no (=0), denoting the child survived during the age-period.

2.1.2. Type of Cooking Fuel

The main exposure variable was type of cooking fuel used in the household. The respondents were asked, “What type of fuel does your household mainly use for cooking?” and in response 12 types of cooking fuel were reported. In the analysis, these fuels were grouped into two categories on the basis of exposure to cooking fuel: “clean fuels” (electricity, liquid petroleum gas, natural gas, and biogas) and “polluting fuels” (kerosene, coal/lignite, charcoal, wood, straw/shrubs/grass, agricultural crops, and animal dung). BDHS analyses have previously classified cooking fuel as “solid” and “non-solid” fuels, where kerosene was categorized in the non-exposed (i.e. “clean fuel”) group [14,24,25]. However, many previous studies have reported kerosene as a polluting fuel and have found significant associations between under-five mortality and respiratory illness among children and kerosene fuel use [26,27,28]. For this reason, kerosene was categorized in the polluting fuels group.

2.1.3. Potential Confounders

A household wealth index (categorized as “high income”, “middle income” or “low income”), mother´s education (categorized as “secondary or higher”, “primary” or “no education”) and mother´s working status (“working” or “not working”) were included as markers of socio-economic status, and have previously been identified as potential confounders [27,28,29,30,31,32,33]. The household wealth index was constructed using principal components analysis, with weights for the wealth index calculated by giving scores to the asset variables such as ownership of transport, durable goods and facilities in the household [14,24,25,34]. “Low income” referred to the bottom 40% of households, “middle income” referred to the middle 40% of households, and “high income” referred to the top 20% of households, based on the approach described by Filmer and Pritchett [34]. Mother´s age (age < 20, 20–29, 30–39 or 40–49 years) and wall material of household (“cement/brick” or “non-cement/non-brick”) were also considered as potential confounders of the association between HAP and under-five mortality.

Place of residence (categorized as “urban” or “rural”), breastfeeding status (categorized as ever breastfed “yes” or “no”) of children and location of kitchen (categorized as “separate building/outdoors” or “in the house”) were also considered a priori factors that may indicate different levels of exposure to polluting fuels. While not necessarily a modifiable risk factor, place of residence is likely to play an important role in child survival as rural children have a higher risk of death from use of polluting fuels than urban counterparts [27,29,31,32,35,36], and an inside kitchen as an indicator of proximity to polluting fuel use has also been shown to be an important factor associated with greater exposure to HAP [18,20,21,22,29,32,37]. Additionally, breastfeeding has been shown to be a protective factor for under-five mortality, generally in infants [28,29,38,39,40,41], which may attenuate the higher risk associated with HAP exposure. Hence, analyses sought to determine whether the magnitude of the association between HAP and under-five mortality differed by past breastfeeding status.

2.2. Statistical Analysis

The association between type of cooking fuels and under-five mortality was investigated using a series of multilevel logistic regression models adjusted for the potential confounders of household wealth, place of residence, mother´s age, mother´s education, mother´s working status, breastfeeding status and wall material of house. Changes in neonatal, infant and under-five mortality rates from HAP over time were also investigated using a trend analysis across 2004, 2007 and 2011 BDHS data by specifying “period” as a continuous variable. To identify the overall effect of HAP from cooking fuels with neonatal, infant and under-five mortality, pooled analyses were also conducted. The extent of divergence or convergence between the slopes of period specific trends within each variable over the study period (2004–2011) was assessed by testing the interaction between period and a given confounding variable using likelihood ratio tests.

Stratified analyses were also conducted by urban and rural areas, breastfeeding status and by location of kitchen (for 2007–2011 only, where information on location of kitchen was available) to determine whether the magnitude of the effect of the exposure on outcomes differed across levels of these variables. Geographical region (“urban” or “rural”), breastfeeding status (ever breastfed “ yes” or “no”) and location of kitchen (“separate building/outdoors” or “in the house”) were each also combined with type of cooking fuel as composite ordinal variables to investigate different level of exposure to HAP for under-five mortality outcomes.

The “Svy” command was used for calculating weighted cumulative incidence estimates of mortality to adjust for the cluster sampling survey design. Multilevel logistic regression models were conducted by using the “xtlogit” command and for likelihood ratio test for interaction “lrtest” command was used. All analyses were carried out in STATA version 13.1 (Stata Corp: College Station, TX, USA).

2.3. Ethics

The DHS project sought and obtained the required ethical approvals from ethics committees in Bangladesh before the surveys were conducted. Informed consent was obtained from study participants before they were allowed to participate in the surveys. The survey data sets used in this study were completely anonymous with regard to participate identity.

The under-five mortality rate decreased from 6.5% in 2004 to 4.4% in 2011, infant mortality rate from 5.5% in 2004 to 4.0% in 2011, and the neonatal mortality rate from 3.6% in 2004 to 3.0% in 2011 (Figure 1). Use of polluting fuels for cooking was associated with a higher risk of neonatal mortality (OR = 1.49, 95% CI = 1.01–2.22, p = 0.043) than infant (OR = 1.27, 95% CI = 0.91–1.77, p = 0.157) and under-five mortality (OR = 1.14, 95% CI = 0.83–1.55, p = 0.422) after adjusting for household wealth, place of residence, mother´s age, mother´s education, mother´s working status, breastfeeding status and wall material of house (Table 1).