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Indoor Air Pollution in Developing Countries and Acute Respiratory Infection in Children

by M.R. Pandey, J.S.M. Boleij, KR. Smith, E.M. Wafula

Edited from "The Lancet" February 25, 1989

Respiratory diseases are the main cause of morbidity and mortality in children in developing countries. Among these diseases, acute respiratory infections (ARI) are responsible for nearly a third of all childhood deaths under 5 years of age. Although immunisation and case-management are partly effective in ARI, it seems clear that long-term solutions will depend on the control of risk factors. Such control, for example, led to striking decreases of moderate and severe ARI in the developed countries long before effective case-management became available. Widespread case-management would be expensive and not an answer in the longterm since mild ARI can progress through moderate and severe phases to death, often in only 2-3 days. In areas without carefully implemented case-management programmes, antibiotics, even if available, are likely to be given too early, leading to drug resistance, or too late.

There are several important risk factors for ARI, including poor nutrition, overcrowding, low birthweight and personal hygiene. In developed countries, air pollution has also been identified as a factor, particularly environmental tobacco smoke(ETS) for ARI in young children. In many developing countries, in addition to an increasing amount of tobacco smoke, many homes contain high levels of smoke from the combustion of biofuels such as wood, crop residues and animal dung for cooking or heating. In about half the world's households such fuels are used for cooking daily, usually without a flue or chimney and with poor ventilation.

Investigations

Results of investigations in 6 developing countries have shown the range of indoor pollution in such circumstances (see table overleaf). Although thousands of chemicals are found in tobacco and biofuel smoke, the best single indicator for comparison of toxic non-carcinogenic effects is probably respirable particulates, similar to tar reported for cigarette emissions. Results of studies in animals suggest any difference in respiratory-system toxicity according to mass is not likely to be large.

As shown in the table, indoor particulate concentrations in rural areas of developing countries, where ARI morbidity and mortality are highest, range from a few hundred to more than 10,000 ug/m³, although different techniques and averaging times were used in the studies reported. In some of the studies other pollutants were also measured, including carbon monoxide and benzoapyrene (sometimes found in concentrations well above those in public settings in developed countries) as well as nitrogen and sulfur oxides, and formaldehyde (found in concentrations at roughly the upper levels of those measured indoors in developing countries). By comparison, ETS levels are about 1 ug/m³ for each cigarette smoked per day. Peak indoor concentrations during the day are about three times higher than this value, and even higher levels may be reached for short periods in the immediate vicinity of smokers. Thus, on the sparse evidence, peak and daily exposures to indoor particulate levels in villages in developing countries would seem to be some twenty times greater than in developed countries.

The results of a semi-quantitative epidemiological study in Nepal showed a direct relation between reported hours per day spent near the stove by infants and children aged under 2 years and episodes of life-threatening ARI. If the many possible confounding factors are discounted, extrapolation shows that by moving all children into the lowest smoke exposure group as much as 25% of moderate and severe ARI would be eliminated. The results of two studies in Africa did not show a relation between ARI and indoor pollution concentrations; this finding is not surprising since there was little variation in smoke exposures among households and the sample sizes were small.

Extrapolation from studies of ARI and ETS also indicates indirectly the potential effect of indoor smoke from biofuels. Contrary to the usual situation, however, it is necessary to extrapolate from low to high doses because of the lack of epidemiological information about smoke and ARI. Some ETS studies have found a dose-response relation between the number of cigarettes smoked in the home and respiratory symptoms in children. Ferris et al, for example, found a risk factor of about two for several symptoms at household levels of 50 cigarettes per day. Fergusson et al reported a linear dose-response relation of three ARI episodes per 5 cigarettes daily per 100 child-years. On the assumptions that the respirable particles in biofuel smoke are half as toxic as those from cigarettes, a 24-h ETS level of 1 ug/m³ per cigarette, and a linear dose-response relation, a child in The Gambia exposed to 1600 ug/m³ would have about 5extra attacks of ARI per year. At these levels, however, an impact on severity as well as frequency could be expected.

Biofuel smoke is thus likely to be a factor in ARI, but its importance in relation to other risk factors is not easily established. Prevention of ARI could well be best achieved by first addressing other risk factors or by addressing smoke solely in the context of broad based programmes for several risk factors. The studies done so far indicate that a longitudinal intervention study for at least 2 years (to include the seasons before and after intervention) would be most likely to produce scientifically sound and useful results. Natural controls are difficult to identify because of the many confounding variables.


FIGURE

Ameliorative measures should be encouraged as part of rural energy, housing, and health programmes. In the long term, cleaner fuels and different kitchen design offer the best solutions, along the lines of such changes in the developed countries. In poor countries where economic and resource constraints are likely to persist for many years, however, less expensive interim measures are warranted. There are promising programmes to promote the use of better cookstoves to save fuel and improve efficiency as well as health. To be successful, such programmes should be designed for local circumstances and should encourage local participation. In some places manufactured metal stoves with high quality control maybe appropriate; in others, locally made stoves of mud and clay may be more suitable. Although they ideally bring enough fuel and labour savings to be economically attractive to households, where needed, improved stoves should also be considered for public subsidy because of their potential health benefits.