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Household air pollution and under-five mortality in India (1992–2006)

Friday, 29th of April 2016

Household air pollution and under-five mortality in India (1992–2006)

Sabrina Naz, Andrew Page, and Kingsley Emwinyore Agho

Excerpts below; full text is at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4845508/

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Background

Household air pollution (HAP) - predominantly from cooking fuel is a major public health hazard and one of the leading causes of respiratory illness and deaths among children under-five years in India. This study investigates the association between HAP from cooking fuel and under-five mortality using India’s National Family and Health Survey (NFHS) datasets over the period 1992–2006 (total of 166,382 children), and the extent to which the association differed by environmental and behavioral factors affecting level of exposure.

Methods

The association between HAP and under-five mortality of three age-groups (neonatal age between 0–28 days, post-neonatal age between 1–11 months and children aged between 12–59 months) was examined using multi-level logistic regression models.

Results

HAP was associated with mortality among children aged under-five (OR = 1.30, 95%CI = 1.18-1.43, P < 0.001) and was more strongly associated in sub-group analyses of post-neonatal mortality (OR = 1.42, 95%CI = 1.19-1.71, P < 0.001) and child mortality (OR = 1.42, 95%CI = 1.05-1.91, P = 0.021) than neonatal mortality (OR = 1.23, 95%CI = 1.09-1.39, P = 0.001). The association was stronger for households in rural areas and for households without a separate kitchen using polluting fuel, and in women who had never breastfed for all age-groups.

Conclusion

Use of cooking fuel in the household is associated with increased risk of mortality in children aged under-five years. Factors relating to access to clean fuels, improvements in infrastructure and household design and behavioral factors are discussed, and can result in further declines in under-five mortality in India.

Keywords: Household air pollution, Under-five mortality, Child mortality, Cooking fuel, India

 

India is the second most populous and seventh largest country by area in the world located in South Asia, and currently is one of the ten fastest growing economies in the world [1]. In the last five decades in India, there has been extensive improvement in poverty reduction, literacy, health standards and human development, however, there remains significant population challenges in relating to health and sanitation [1]. More than 90 % of the rural population and 31 % of the urban population in India still rely primarily on solid fuels as a domestic source of energy [1–3]. Household air pollution (HAP) from solid fuels (such as wood, animal dung, crop residues, charcoal and coal) for cooking and heating is a substantial cause of respiratory illness and death, due to a range health damaging pollutants such as fine particles, carbon monoxide (CO₂₎, nitrogen oxides (NO₂₎, sulphur dioxide (SO_2), benzene, butadiene, formaldehyde, polyaromatic hydro-carbons and a number of other chemicals, [4, 5] and remains a major public health concern in the developing world [6, 7]. A recent study from India indicated that 56 % of children aged under-five remained with their mother at all times during cooking [2], and that proximity to smoke from solid fuel use is associated with an increase in the risk of health problems among young children [8, 9].

According to World Health Organization (WHO), 3.5 % of the total burden of disease in India country has been attributable to HAP [10] and a previous study from India has indicated that solid fuel use was responsible for 20 % of deaths among children <5 years [11, 12]. In addition, 24 % of total deaths among children under five in India was associated with acute respiratory illness (ARIs) [12, 13] which has also been identified as the leading cause of death of children less than five by the 2010 Global Burden of disease (GBD) study [14]. The under-five mortality in India declined from 125 per 1,000 live births in 1990 to 74.6 per 1,000 live births in 2005–06 [15], and despite projections that it will further decline to 70 per 1,000 live births by 2015, this still does not achieve the Millennium Development Goal 4 (MDG4) target of 42 per 1,000 live births to reduce mortality among children under five by two-thirds [15].

A number of previous studies in India have reported the effects of HAP on respiratory diseases among young children [12, 16–20] and associations between HAP and under-five mortality with other health outcomes (e.g., low birth weight, respiratory illnesses among young children) [11, 21–23]. However, those studies have been limited to surveys of limited geographic areas, or hospital based data sources for specific regional populations or focused on all types of HAP (for example, including tobacco use), and not exclusively cooking fuel [24–29]. To date, no studies in India have examined changes in the association between HAP and under-five mortality over time, or investigated the role of environmental and behavioural factors that might affect the level of exposure to HAP (for example, place of residence, location of kitchen, and breastfeeding status). Accordingly, the objective of this study was to investigate trends in the association between HAP from cooking fuel and under-five mortality for three consecutive age groups (neonatal, post-neonatal and child), and to assess how this is affected by key environmental and behavioral factors using large-scale nationally representative data over the period 1992–2006.

Data sources

The data in this study were extracted from India´s National Family and Health Survey (NFHS) datasets for the years 1992–93 (NFHS-1), 1998–99 (NFHS-2) and 2005–06 (NFHS-3). The NFHS are nationwide surveys based on a representative sample of households throughout the country under the authority of the Ministry of Health and Family Welfare (MOHFW), Government of India, and implemented by the International Institute for Population Sciences (IIPS), Mumbai with technical assistance from Macro International of Calverton, Maryland, USA, as a part of its Demographic and Health Surveys Program [1, 30,31]. To date, the three NFHS surveys (NFHS-1, NFHS-2 & NFHS-3) have collected demographic and health data by interviewing ever-married women (aged 15–49 years) and men (aged 15–54 years) using a stratified sample of households based on a two-stage cluster design [1, 30, 31]. NFHS-3 covered all 29 states of India, which includes more than 99 % of India´s population [1].

A total of 303,361 ever-married women of reproductive age (112,357 from urban and 191,009 from rural areas) were included in the three datasets with a response rate of 95.4 % in women across the three datasets (NFHS-1, NFHS-2 and NFHS-3). This study was based on information relating to 166,382 singleton live-born children, of whom 11,311 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.

Study outcomes

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

• 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
• Post-neonatal mortality: The number of deaths between one month and the first birthday (1–11 months). Defined as, Number of post-neonatal deaths/Total number of live births
• Child mortality: The number of deaths between exact ages one and five (12–59 months). Defined as, Number of child 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 these any three periods of age or no (=0) denoting the child survived during the age-period.

Exposure to 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 smoke: “clean fuels” (electricity, liquid petroleum gas (LPG), natural gas and biogas) and “polluting fuels” (kerosene, coal/lignite, charcoal, wood, straw/shrubs/grass, agricultural crop waste and dung cakes). NFHS analyses have previously classified cooking fuel as “solid” and “non-solid” fuels, where kerosene was categorised in the non-exposed (i.e. “clean fuel”) group [1, 30, 31]. However, some previous studies have reported kerosene as a polluting fuel and have found significant associations between under-five mortality or respiratory illness among children and kerosene fuel use [21, 32, 33]. For this reason, kerosene was categorised in the polluting fuels group.

Potential confounders

Place of residence (categorized as “urban” or “rural”), household wealth index (categorized as “high income”, “middle income” or “low income”), mother´s education (categorized as “secondary or higher”, “primary” or “no education”), mother´s working status (categorized as “working” or “not working”) and type of house (categorized as “pucca”, “semi-pucca” or “kachha”) were included as markers of socio-economic status, and have previously been identified as potential confounders of the association between HAP and under-five mortality [11, 21–23, 33–38]. 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 [1, 30, 31, 39]. “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 [39]. Mother´s age (categorized as <20, 20–29, 30–39 and 40–49 years) and sex of the child (categorized as “female” or “male”) were also considered as potential confounders of the association between HAP and under-five mortality.

Breastfeeding status of mother (categorized as ever breastfed “yes” or “no”) and location of kitchen (categorized as separate room used as kitchen “yes” or “no”) were also considered a priori factors that may indicate different levels of exposure to polluting fuels. No separate kitchen used for cooking in the household as an indicator of proximity to polluting fuel use has also been presented to be an significant factor associated with high exposure to HAP [24, 26–28, 36, 37, 40]. Additionally, breastfeeding has been shown to be a protective factor for under-five mortality, generally in neonatal and infancy period [33, 34, 41–44] which may reduce the greater risk of exposure associated with HAP. Hence, analyses sought to determine whether the magnitude of the association between HAP and under-five mortality differed by past breastfeeding status.

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, sex of child, breastfeeding status, kitchen location and type of house. Changes in neonatal, post neonatal and child mortality incidences from HAP over time were also investigated using a trend analysis across 1992–93, 1998–99 and 2005–06 NFHS data by specifying ´period´ as a continuous variable. To identify the overall effect of HAP from cooking fuels with neonatal, post-neonatal and child 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 (1992–2006) was assessed by testing the interaction between period and a given confounding variable using likelihood ratio tests.

Stratified analyses were also conducted by breastfeeding status and by location of kitchen to determine whether the magnitude of the effect of the exposure on outcomes differed across levels of these variables. Breastfeeding status (ever breastfed “yes” or “no”) and location of kitchen (separate room used as kitchen “yes” or “no”) 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. Random effects multilevel logistic regression models were conducted by using the “xtlogit” command and for likelihood ratio test for interaction “lrtest” command was used. Adjusted risk differences were also estimated from logistic regression model using the “margins” command. All analyses were carried out in STATA version 13.1 (Stata Corp: College Station, TX, USA).

Ethics

The Demography and Health Survey (DHS) project sought and obtained the required ethical approvals from ethics committees in India before the surveys were conducted. Informed consent was obtained from study participants before their participation in the surveys. Publicly available, de-identified datasets were used in this study following approval from The DHS Program.

The overall under-five mortality incidence proportion in India decreased from 8.7 % per year in 1992 to 6.6 % per year in 2006 for those using polluting fuels for cooking. Decreasing trends were also evident for each age group, where the neonatal mortality incidence proportion declined from 4.5 % in 1992 to 3.9 % in 2006, post-neonatal mortality incidence proportion from 2.7 % in 1992 to 1.7 % in 2006 and child mortality incidence proportion from 1.5 % in 1992 to 0.9 % in 2006 (Fig. 1). Use of polluting fuels (kerosene, coal/lignite, charcoal, wood, straw/shrubs/grass, agricultural crop waste and dung cakes) for cooking was associated with a higher risk of post-neonatal (OR = 1.42, 95%CI = 1.19-1.71, P < 0.001) and child mortality (OR = 1.42, 95%CI = 1.05-1.91, P = 0.021) than neonatal mortality (OR = 1.23, 95%CI = 1.09-1.39, P = 0.001) after adjusting for household wealth, place of residence, mother´s age, mother´s education, mother´s working status, sex of child, breastfeeding status, kitchen location and type of house (Table 1). Use of polluting fuels and under-five mortality showed statistically significant association (OR = 1.30, 95%CI = 1.18-1.43, P < 0.001) after adjusting for confounders (Fig. 2). Corresponding risk differences between use of clean fuel and polluting fuel were found (0.68 %, 95%CI = 0.33 %-1.03 %) for neonatal, (0.61 %, 95%CI = 0.35 %-0.87 %) for post-neonatal, (0.34 %, 95%CI = 0.28 %-0.40 %) for child mortality and (1.50 %, 95%CI = 1.01 %-1.99 %) for overall under-five mortality.

Stratified analyses to examine different levels of exposure to HAbP showed more than 5-fold greater risk of mortality in women who never breastfeed and who used polluting fuels for cooking (compared to breastfeeding women who used clean fuels), with robust associations evident for child (OR = 10.47 95%CI = 7.13-15.37, P < 0.001) and post-neonatal (OR = 8.87 95%CI = 6.94-11.33, P < 0.001) mortality than neonatal (OR = 5.36 95%CI = 4.65-6.19, P < 0.001) mortality (Table 2). In addition, the risk of under-five mortality was also higher for the women who ever breastfed but used polluting fuel for cooking (Table 2).