Effect of reduction in household air pollution on childhood pneumonia in Guatemala (RESPIRE): a randomised controlled trial

Summary

Background

Pneumonia causes more child deaths than does any other disease. Observational studies have indicated that smoke from household solid fuel is a significant risk factor that affects about half the world's children. We investigated whether an intervention to lower indoor wood smoke emissions would reduce pneumonia in children.

Methods

We undertook a parallel randomised controlled trial in highland Guatemala, in a population using open indoor wood fires for cooking. We randomly assigned 534 households with a pregnant woman or young infant to receive a woodstove with chimney (n=269) or to remain as controls using open woodfires (n=265), by concealed permuted blocks of ten homes. Fieldworkers visited homes every week until children were aged 18 months to record the child's health status. Sick children with cough and fast breathing, or signs of severe illness were referred to study physicians, masked to intervention status, for clinical examination. The primary outcome was physician-diagnosed pneumonia, without use of a chest radiograph. Analysis was by intention to treat (ITT). Infant 48-h carbon monoxide measurements were used for exposure-response analysis after adjustment for covariates. This trial is registered, number ISRCTN29007941.

Findings

During 29 125 child-weeks of surveillance of 265 intervention and 253 control children, there were 124 physician-diagnosed pneumonia cases in intervention households and 139 in control households (rate ratio [RR] 0·84, 95% CI 0·63–1·13; p=0·257). After multiple imputation, there were 149 cases in intervention households and 180 in controls (0·78, 0·59–1·06, p=0·095; reduction 22%, 95% CI −6% to 41%). ITT analysis was undertaken for secondary outcomes: all and severe fieldworker-assessed pneumonia; severe (hypoxaemic) physician-diagnosed pneumonia; and radiologically confirmed, RSV-negative, and RSV-positive pneumonia, both total and severe. We recorded significant reductions in the intervention group for three severe outcomes—fieldworker-assessed, physician-diagnosed, and RSV-negative pneumonia—but not for others. We identified no adverse effects from the intervention. The chimney stove reduced exposure by 50% on average (from 2·2 to 1·1 ppm carbon monoxide), but exposure distributions for the two groups overlapped substantially. In exposure-response analysis, a 50% exposure reduction was significantly associated with physician-diagnosed pneumonia (RR 0·82, 0·70–0·98), the greater precision resulting from less exposure misclassification compared with use of stove type alone in ITT analysis.

Interpretation

In a population heavily exposed to wood smoke from cooking, a reduction in exposure achieved with chimney stoves did not significantly reduce physician-diagnosed pneumonia for children younger than 18 months. The significant reduction of a third in severe pneumonia, however, if confirmed, could have important implications for reduction of child mortality. The significant exposure-response associations contribute to causal inference and suggest that stove or fuel interventions producing lower average exposures than these chimney stoves might be needed to substantially reduce pneumonia in populations heavily exposed to biomass fuel air pollution.

Funding

US National Institute of Environmental Health Sciences and WHO.

Introduction

Acute lower respiratory infection (ALRI) is the leading cause of death in children, with most fatal cases occurring as pneumonia in children younger than 5 years in developing countries.¹ Poverty is thought to be the primary cause, which manifests as malnutrition, including micronutrient deficiencies, and limited access to medical care.² Another attribute of poverty is household air pollution from use of unprocessed biomass fuels (wood, animal dung, and crop wastes) and coal in simple stoves.³ Findings from a meta-analysis of published observational studies showed that young children exposed to smoke from use of household biomass fuel had a rate of ALRI twice that of children not exposed or when cleaner fuels were used.⁴ Furthermore, studies have shown that ALRI risks are associated with short-term air pollution measurements⁵ and other indicators of exposure.6, 7, 8

The substantial indoor concentrations of important health-damaging pollutants that result from the use of these fuels are thought to explain the relation with ALRI. As with tobacco smoke, there are thousands of compounds in gaseous and aerosol forms in biomass fuel smoke, including several with effects that include immune system suppression, severe irritation, inflammation, ciliary dysfunction, and carcinogenicity.⁹ Small particles are typically used as an indicator of the health risk for these mixtures, and are commonly present in households using biomass fuels without effective chimneys at concentrations ten to 100 times higher than is recommended in health-based guidelines.10, 11

Viral agents have an important role in ALRI, although most deaths are thought to arise through bacterial infection, which can occur with or without initial viral infection.¹² Of the viral agents, respiratory syncytial virus (RSV) is the most common in young children, although its incidence varies by season.13, 14 Evidence about the relation between exposure to biomass fuel smoke and risk of RSV illness is conflicting.¹⁵ One study from The Gambia¹⁶ reported reduced risk of severe RSV illness with increased exposure to cooking smoke, raising the possibility of a differential effect of household air pollution on viral and bacterial ALRI.

The evidence of ALRI risk associated with biomass fuel use is limited by several methodological issues.15, 17 Previous studies used observational designs, which have the inherent difficulty of residual confounding from the association between biomass fuel use and other poverty-related ALRI risk factors, particularly nutrition. Studies used hospital-based or community-based case-finding; those using hospital-based case-finding were susceptible to selection bias because of differences in health-care seeking behaviour, whereas those using community-based case-finding probably misclassified as ALRI many upper respiratory tract infections, which are more common, can have a different relation with air pollution, and do not cause substantial morbidity or mortality.¹⁸ Since few studies have assessed indicators of ALRI severity (eg, hypoxaemia), and none has attempted to differentiate all ALRI by aetiological agent (viral vs bacterial), the effect of household air pollution on factors that are known to increase case fatality has not been possible to assess.¹⁹ None of the studies directly assessed long-term air pollution exposures, relying instead on indirect exposure indicators such as fuel or stove type, or whether a child is carried on the mother's back during cooking—methods that are inevitably associated with substantial exposure misclassification. Finally, the absence of masking could have led to bias—eg, when interviewing parents about exposure history in case-control studies. Although studies have shown associations between ambient air pollution and child ALRI, most were set in developed countries, where the epidemiology of child pneumonia and associated risk factors differs greatly from that in developing countries.²⁰

We report on RESPIRE (Randomised Exposure Study of Pollution Indoors and Respiratory Effects), a randomised controlled trial to assess whether a specific intervention to lower indoor wood smoke emissions would reduce child pneumonia.