Indoor air pollution from biomass combustion and acute respiratory infections in Kenya: an exposure-response study

doi:10.1016/S0140-6736(01)05777-4

The Lancet

Volume 358, Issue 9282, 25 August 2001, Pages 619-624

https://doi.org/10.1016/S0140-6736(01)05777-4 Get rights and content

Summary

Background

Acute respiratory infections (ARI) are the leading cause of the global burden of disease and have been causally linked with exposure to pollutants from domestic biomass fuels in less-developed countries. We used longitudinal health data coupled with detailed monitoring of personal exposure from more than 2 years of field measurements in rural Kenya to estimate the exposure-response relation for particulates smaller than 10 μm in diameter (PM₁₀) generated from biomass combustion.

Methods

55 randomly-selected households (including 93 infants and children, 229 individuals between 5 and 49 years of age, and 23 aged 50 or older) in central Kenya were followed up for more than 2 years. Longitudinal data on ARI and acute lower respiratory infections (ALRI) were recorded at weekly clinical examinations. Exposure to PM₁₀ was monitored by measurement of PM₁₀ emission concentration and time-activity budgets.

Findings

With the best estimate of the exposure-response relation, we found that ARI and ALRI are increasing concave functions of average daily exposure to PM₁₀, with the rate of increase declining for exposures above about 1000–2000 μg/m³. After we had included high-intensity exposure episodes, sex was no longer a significant predictor of ARI and ALRI.

Interpretation

The benefits of reduced exposure to PM₁₀ are larger for average exposure less than about 1000–2000 μg/m³. Our findings have important consequences for international public-health policies, energy and combustion research, and technology transfer efforts that affect more than 2 billion people worldwide.

Introduction

Acute respiratory infections (ARI) are the leading cause of the global burden of disease,1, 2 accounting for more than 6% of worldwide disease and mortality, mostly in less-developed countries. Between 1997 and 1999, acute lower respiratory infections (ALRI) caused 3·5–4·0 million deaths worldwide1, 2, 3 —more than that caused by any other infectious disease. Exposure to indoor air pollution, especially to particulate matter, from combustion of biofuels (wood, charcoal, agricultural residues, and dung), has been associated with respiratory disease in less-developed countries.4, 5, 6, 7, 8, 9 More than 2 billion people use biomass as their main source of domestic energy; hence international development and public-health organisations have sought to implement preventive measures to reduce this exposure. The exposure-response relation between indoor air pollution from biomass combustion and ARI is important for assessment of the benefits and effectiveness of preventive measures such as design and dissemination of improved stoves and fuels.

Health impacts of outdoor (ambient) particulate matter in urban areas of industrialised countries have been identified and quantified in epidemiological and physiological studies¹⁰ in the past two decades. However, these results are applicable to a small range of exposures, mostly less than 200 μg/m³, which are mainly of concern in industrialised countries. The exposure-response relation at concentrations of hundreds or thousands of μg/m³, which are typical of indoor environments in less developed countries,¹¹ is relatively unknown. Because around 80% of total global exposure to particulate matter occurs indoors in developing nations,12, 13 we need to assess this relation at exposure levels typical of these settings.

Research on the health effects of indoor air pollution in less-developed countries has been hindered by lack of detailed data about exposure and illness outcomes. In many epidemiological studies, researchers14, 15, 16, 17, 18, 19, 20 have used indirect measures of personal exposure, such as fuel or housing type. Because biomass fuels are very common in rural areas, in this indirect approach to exposure estimation many people are grouped into a single exposure category. Recent findings on large variations in emissions from individual stove types,11, 21 and in exposure profiles within individual households,22, 23, 24 suggest that such indirect analysis and grouping of individuals reduces the reliability of estimation of exposure-response relations.

We directly examined the exposure-response relation for indoor air pollution and ARI in developing countries in a field study in rural Kenya. Our work was part of a long-term study of the relation between energy technology, indoor air pollution, and public health. We simultaneously monitored exposure to indoor air pollution and health status of individuals for more than 2 years to quantify the exposure-response relation for health and indoor particulate matter for a continuous range of exposure concentrations.

Section snippets

Participants

The study took place at Mpala Ranch and Research Centre, in Laikipia District, central Kenya. Cattle herding and domestic labour are the main occupations of most people who live in the 80–100 households (about 500 individuals) on the ranch; the rest work as maintenance staff. Firewood and charcoal were the main fuels used by the study group (consisting of all households on the ranch). Study households had similar tribal backgrounds (Turkana and Samburu), economic status, and diet. Houses in

Results

Table 1 contains demographic information for individuals from the 55 study households, and mean (SD) number of health reports obtained. Figure 2 shows ARI (divided into AURI and ALRI)—mean fraction of weekly examinations in which an individual was diagnosed with either infection—stratified by demographic subgroup. Differences between female and male ARI rates by two-sided two-sample t test were not significant for children aged 4 years and under but were for other age groups: p=0·02, 5–14

Discussion

We have shown that increased exposure to indoor PM₁₀ increases the frequency of ARI. Rate of increase of exposure-response is highest for exposures below 1000–2000 μg/m³. Although this concave shape of the exposure-response relation fell inside 95% CI, it was confirmed by analysis with a continuous exposure variable. This result suggests that public-health programmes to reduce adverse impacts of indoor air pollution in developing countries should concentrate on measures that reduce average

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ArticlesIndoor air pollution from biomass combustion and acute respiratory infections in Kenya: an exposure-response study

Summary

Background

Methods

Findings

Interpretation

Introduction

Section snippets

Participants

Results

Discussion

Environ Int

Biomass Bioenergy

Atmos Environ

Atmos Environ

World health report

World health report 2000. Health systems: improving performance

World Health report

Indoor air pollution in developing countries

World Health Stat Q

Risk factors for mortality from acute lower respiratory tract infections in young Gambian children

Int J Epidemiol

Cooking fuel smoke and respiratory symptoms among women in low-income areas in Maputo

Environ Health Perspect

Domestic smoke pollution and chronic bronchitis in a rural community of the hill region of Nepal

Thorax

Indoor air pollution in developing countries and acute lower respiratory infections in children

Thorax

Comparison of emissions and residential exposure from traditional and improved biofuel stoves in rural Kenya

Environ Sci Tech

Air pollution: assessing total exposure in developing countries

Environment

Articles
Indoor air pollution from biomass combustion and acute respiratory infections in Kenya: an exposure-response study