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

Background a critical review of the quantitative literature linking indoor air pollution caused by household use of biomass fuels to acute respiratory infections in young children, with emphasis but not limited, children under 2 years of age in less developed countries have acute lower respiratory infections and pneumonia.
More than 2 out of 5 households in the world use wood, crop residues and biomass in the form of animal feces as the primary fuel.
Methods use Medline and other electronic databases, but it is also necessary to obtain the literature from colleagues in less developed countries, where none of the publications have an international index yet.
Results The study of indoor air pollution by household biomass fuels was reasonably consistent, and as a group, the risk of exposure to young children was significantly increased compared to those who used cleaner fuels or exposed less.
Not all studies have been able to adapt to mixed factors, but most of the studies that have done so have found that there are still huge risks.
Conclusion The relative risk seems to be great for the risks considered here.
Since acute lower respiratory tract infection is the main cause of child death in less developed countries, for the world population, it bears a greater burden of disease than any other disease category, due to widespread exposure such as air pollution, even small additional risks can have a significant impact on public health.
In households using biomass fuels, the risk of indoor air pollution also appears to be considerable, presumably because of the high concentration of pollutants found in such environments, and young children and mothers have been cooking for a long time together.
Given the large number of vulnerable groups at risk, there is an urgent need for randomized trials to increase confidence in the cause
Effect relationships, quantify risks more accurately, determine the degree of exposure reduction required to significantly improve health, and determine the effectiveness of interventions.
At the beginning of the 20 th century, the dramatic events of outdoor air pollution in developed countries showed that air pollution may lead to excessive deaths, and the risk of children in high pollution periods may be particularly high.
For example, during the heavy fog in London in 1952, it was mainly due to smoke from coal-fired household stoves, killing nine thousand people.
It was noted that the risk of infants, young children and the elderly was higher than others, and the proportion of deaths caused by respiratory causes increased compared to weeks before and after smog.
Outdoor air pollution has now been examined as a risk factor for respiratory morbidity and mortality in many epidemiology studies, and the evidence continues to indicate the risk of adverse effects for infants and young children. 811-
Although levels of environmental pollution in developed countries have now declined, the epidemiology evidence still suggests adverse effects on both respiratory morbidity and mortality.
1213 in fact, new studies have shown adverse effects of inhalation particles at levels previously considered safe, which are now often achieved in many urban areas. 1215-
Over the past 20 years, it has also been recognized the potential significance of exposure to air pollutants in indoor environments for children's health. 6718-
Children in the world are exposed to inhaled pollutants when breathing air in different indoor and outdoor places.
Total personal exposure when considering health risks-
It includes all exposure received to the agent regardless of location and media
Is the relevant exposure measures.
The total amount of exposure of 21 individuals to air pollutants can be estimated as a weighted average of pollutant concentrations in the environment in which children are located;
Weights are proportional to the time spent in these environments with different pollutant concentrations.
The concept of pollution exposure, known as the micro-environment model, clarifies the health relevance of indoor and outdoor pollution exposure, and the extensive contribution of indoor and outdoor exposure to the total exposure of children living in different countries of the world, according to source and time-
Activity mode.
It emphasizes that people must make sure to check the pollution that people spend the most time on and where the environment is high. 23-
25. for example, with particulate matter as an indicator pollutant, it is estimated that the total global population exposure is mainly controlled by the home environment in developing countries using solid fuel for cooking and heating.
2526 this is due to the convergence of exposure factors-
That is to say, a large number of people are adjacent to the frequently used equipment with large emission factors.
Crop residues, feces, wood, and coal are widely used worldwide, possibly accounting for about half of the fuel used for cooking every day.
27 judging from the particle level, the outdoor environment of the world's most polluted cities is also in developing countries --
It's worth noting, but not just coal use in Asian cities.
2628 environmental tobacco smoke exposure (ETS)
Tracking tobacco consumption;
Developed countries dominate this trend, but growth rates in these countries are now static or declining, while growth rates in the developing world are stable.
26 This review focuses on the indoor exposure of the world's children to pollution caused by biomass fuel combustion. (
Relevant comments were also made on the ARI risk to children caused by outdoor air pollution caused by smoking and fossil fuel burning. )
The comment does not involve the contamination of indoor air by carbon dioxide generated by stoves and space heaters.
Despite the intense investigation, this indoor pollutant is not in a convincing connection with ARI, but is inconsistent with respiratory symptoms. 29-
31 for example, in the first 18 months of life, a cohort study on carbon dioxide exposure and respiratory diseases found no evidence of increased exposure risk. 32Ackermann-
Liebrich and Rap33 have recently reviewed evidence of indoor exposure to sulfur dioxide.
A brief discussion of the mechanism includes a range of clinical conditions of various causes and severity, which are usually divided into two main forms: upper respiratory tract infection (URI)
Lower respiratory tract infection (ALRI).
The risk of severe ARI is the highest among very young children and the elderly, which can be fatal.
Clinical and epidemiology standards can be used to distinguish between URI and ALRI, but unfortunately there is no uniform accepted standard worldwide and the definitions in use are not exactly consistent.
For research and case management in less developed countries under site conditions, who defines URI as any combination that includes the following symptoms: cough, nasal congestion or runny nose with or without fever, and/or electric discharge of the ear.
URI can usually be successfully treated at home with support therapy.
ALRI includes severe ARI with lung infection, which is the most serious form.
Severe infections are usually caused by bacteria, although they can sometimes be caused by viruses.
The clinical symptoms of ALRI include any of the above symptoms of URI, including rapid breathing and/or chest impact and/or stripes.
Severe ALRI caused by bacteria is treated with antibacterial, and they can sometimes be fatal without antibacterial treatment.
35 air contaminants may increase the incidence of ARI by adversely affecting specific and non-specific contaminants
Specific host defense of respiratory tract against pathogens (table 3). 36 The non-
Specific mechanisms include filtration and removal of particles in the upper airway, mucus fiber devices in the trachea and trachea, swallowed-promoting components of epithelial lining fluid, and through cell swallowing in the airway and lung macrophages and kill infected organisms.
The specific mechanism involves various components of body fluid immunity and cellular immunity.
Organism-specific immunoglobulin promotes swallowing
Cell-mediated immunity is necessary to kill an organism that can survive within the lung's macrophages.
View this table: from a toxicology point of View, viewing the host defense of respiratory tract infection smoke generated by inline View pop-up table 3 household solid fuel is a complex mixture containing many potential related components
These mixtures are highly variable in nature and their properties are determined by the source, the materials burned, the time since they were produced, and other factors.
The chemical and physical properties of these mixtures have been described to some extent, with 73738, in particular, wood smoke from metal heaters used in developed countries.
Therefore, only a summary of the mechanisms by which specific air pollutants may increase the risk of ARI and mixtures can be made
Specific arguments cannot be easily made.
On the other hand, there is sufficient basis for understanding the toxicology properties of these mixtures to conclude that they may reasonably increase the risk of ARI.
Some of the common contaminants in indoor and outdoor air have been shown to adversely affect the components of the defense mechanism.
For example, the particle phase and gas phase components of cigarette smoke adversely affect the function of the mascara muscle in an in vitro model.
The gas components that appear to be important include sulfur dioxide, ammonia, melamine, aldehyde, ketone, aldehyde and acid.
39. it has been shown that nitrogen has an adverse effect on the mucus gland device and on the immune defense of body fluids and cells.
A complex mixture of sulfur dioxide and particles may reduce the efficacy of host defense microorganisms and respiratory inflammation.
Studies have shown that ozone can cause respiratory inflammation, increase airway permeability, and impair the function of macrophages.
41. in animal studies, diesel exhaust was associated with chronic inflammation of the respiratory tract, epithelial cell hyperplasia, impaired lung clearance, pulmonary fibrosis and impaired lung function.
42 exposure to air pollutants may also increase the severity of respiratory infections, thereby increasing the proportion of diseases that are clinically considered to involve the lower respiratory tract, and even increasing morbidity and mortality.
The increase in severity may be mediated by inflammation on the skin surface of the trachea airway tree caused by irritating pollutants.
If persistent exposure to air contaminants causes chronic inflammation, infection may become more severe as infected organisms further damage the airways that have become inflamed and may shrink.
Recently, Thomas and Zelikoff43 have shown that animal exposure to wood smoke significantly alters local and systemic immune responses associated with bacterial infection.
In addition to the intensity of the source, indoor air pollution, the impact of indoor emissions on air quality directly depends on the ventilation and air mixing of the space.
Most houses in developed countries are located in temperate zones, with a relatively low exchange rate for indoor and outdoor air, usually changing air or less every hour.
44 even the low emission rate of this housing can lead to indoor pollutant concentrations at public health levels.
Housing ventilation rates in developing countries mainly located in tropical and subtropical parts of the world may be higher, and these areas are often open to the outdoors.
However, it is easy to find strong sources in developing countries, including biomass (
Wood, crop residue and feces)
Coal-fired for cooking and heating.
Indoor pollutants can be divided into four categories by source: combustion products; semi-
Volatile and volatile organic compounds released by building materials, furniture and chemical products;
Pollutants in soil gases;
And pollutants produced by biological processes.
45 major combustion pollutants include carbon monoxide, nitrogen and sulfur oxides, particles and volatile organic compounds.
Complex mixtures in indoor air generated by smoking are called environmental tobacco smoke (ETS).
A variety of half
Volatile and volatile organic compounds are found in indoor air;
These compounds come from various sources.
The gas generated from the ground below the home may contain contaminants that may adversely affect health, such as radon and triamine.
There are many biological agents in the indoor environment, such as pollen and mold, insects, viruses and bacteria.
While there is no systematic collection of data, the relative importance of the four types of indoor air pollution may vary across the world due to climate and level of development.
For the combustion source, this is the focus of this review and can be summarized.
After smoking, gas stoves have been the most common indoor pollution sources in research in developed countries.
Globally, however, gas stoves are at the high end of the historic evolution of home fuel quality, sometimes called the energy ladder.
46 at the lowest stage, dry animal feces and cleaned branches and grass are used as cooking fuel (fig 1).
The next stage in the sequence is crop residues, wood and charcoal. The first non-
The biomass fuel on the ladder is kerosene or coal, and the bottled and pipe gas and electricity are the highest.
In general, each successive step on this ladder is associated with the improvement of cooking system technology, cleanliness, efficiency and cost.
Download the emissions of the household fuel ladder in Figure 1 of figure open in the new tabDownload powerpoint.
It was copied with the permission of Smith and others.
Nearly half of the world's households are believed to cook on unprocessed solid fuels every day
That is, biomass fuel or coal (fig 2).
A large part of the emissions in households using biomass fuels are discharged into the living area.
Although indoor and outdoor air exchange rates are relatively high in most developing countries, pollutant emission rates for such fuels are also high, so indoor concentrations and associated exposures may be high.
Compared to the gas stove, even a stove that uses wood as a clean biofuels, the pollution released during cooking will increase by 50 times (fig 1).
In addition, in most parts of South Asia and in highland areas of developing countries in Asia, Africa, Latin America and Oceania, unventilated space heating using biomass fuels is common.
China's 25 largest population is exposed to coal fuel smoke burning from simple stoves, which also has a high emission rate.
Download The World Distribution of Household fuel use in figure 2 of figure open in the new tabDownload powerpoint.
Copy with permission from Reddy and others.
Incomplete combustion of unprocessed solid fuels under the operating conditions of a simple stove produces hundreds of compounds.
This complex mixture is produced by burning coal and biomass fuel, although the mixture of compounds in the smoke is different.
Unlike coal, biomass fuels usually contain very little inherent contaminants (
Sulfur, trace metals and Ash)
And, under appropriate conditions, they can be burned without release, except for products that are completely burned (
Carbon dioxide and water).
Unfortunately, it is difficult to create the best conditions for complete combustion with cheap home equipment.
The smoke from the stove is a complex and unstable mixture.
747 biomass fuel smoke contains a large number of several pollutants, and many countries have established outdoor air quality standards for these pollutants
Carbon monoxide, particles, hydrocarbons and nitrogen oxides, for example.
In addition, the aerosol contains many organic compounds, such as formaldehyde, benzene and multi-aromatic hydrocarbons, that are considered toxic or carcinogenic.
The composition of the smoke changes with a slight change in fuel quality, stove structure or combustion properties.
There is sufficient evidence that particles are usually small size particles that are considered to be the most harmful to health.
748 although a large-scale global smoke concentration survey has not yet been conducted, the results of studies in different regions of the world provide an indication of typical indoor concentrations of major pollutants.
Table 4 lists the studies that measure the total number of particles (TSP)or respirable.
49 these indoor levels are surprisingly high compared to the various national standards recommended by the World Health Organization and even to the typical outdoor concentrations in the most polluted cities.
We are currently unable to accurately estimate the total population of developing countries exposed to indoor concentrations, which is considered unacceptable, and we cannot easily allocate the contribution of indoor and outdoor sources to the total exposure of individuals.
In addition, in some rural areas, outdoor pollution permeates the interior to a large extent, and indoor fuel burning may be the main cause of outdoor pollution.
In addition, there is no international standard for indoor pollutant concentration.
Assuming that indoor standards should be at least as strict as outdoor standards, the number of people exposed to unacceptable levels indoors is expected to match or exceed the number of people exposed to unacceptable environmental concentrations in all cities of the world.
50 consider time-
The mode of activity is far more than spending more time indoors and outdoors, indicating the global total dose equivalent (
Actual suction volume)
Indoor pollution may be an order of magnitude larger than environmental pollution.
25 View this table: View inline View pop-up table 4 indoor air pollution epidemiology caused by biofuels combustion in developing countries (
Annotated bibliography on ARI and indoor air quality (non-ETS)
See maclaken and Smith. 51)
The first report in the biomedical literature describing the association between indoor cooking smoke and pneumonia in children in developing countries reported on the University of Lagos's measurement teaching hospital for infant home indoor pollution levels diagnosed with maoitis and pneumonia
52 The extremely high average level of various gas pollutants was measured, with an average exposure time of 3.
It is estimated that 1 hour per day, but unfortunately, no differences in home exposure levels using wood, kerosene, coal and natural gas were reported, and no infant control group.
Therefore, it is difficult to draw any quantitative conclusions about the relationship between exposure and the incidence of pneumonia.
To draw attention in this review, we were able to identify 13 recently published studies that quantitatively discuss the relationship between exposure of young children in developing countries to household biomass smoke and ALRI (table 5)
In the ALRI case selection, it reasonably meets the WHO or other authoritative criteria established at the time of the study.
These standards have changed over time, and as such, the studies are not exactly consistent as described below.
Our judgment, however, is that the protocols in these 13 studies are sufficiently strict to warrant that they are considered as part of the same repository of evidence.
Nine times in Africa, one in India, one in Brazil, one in Argentina and one in Nepal.
Only one case of death was handled and the others were treated with the incidence.
In addition, we found two studies from developed countries (USA)
Relationship between wood smoke and ALRI in Navaho children's families (table 6).
These 15 studies are of particular concern as they relate to the actual ALRI of children under the age of five, although confirmed in different ways and involve indoor exposure to biomass fuel smoke.
Each has a sufficient number to calculate the odds and confidence intervals.
Table 7 summarizes the results of these 15 studies.
View this table: view inline View pop-up table 5 biomass fuel use and ALRI for children under 5 years of age in developing countries View inline View pop-up table 6 timber burning and ALRI for children under 5 years of age in developed countries View this table: view inline View pop-up table 7 in developing countries, ALRI's research summary in young children and related studies on indoor biomass smoke although briefly discussed below, are not discussed in detail here, because they only meet some criteria-
For example, address the risk to older children, address respiratory symptoms, but do not confirm ALRI, or provide sufficient information to calculate the odds.
13 studies showed different rates of ALRI among young children in developing countries. table 5).
Two and one potential case in cohort study 5354-
Control Study 55 used reported shortness of breath to screen children with lower respiratory disease.
The first two were to assess the severity by calculating the frequency of breathing and assessing signs of chest breathing and heart and lung failure.
55 cases were confirmed by laboratory tests and angiography.
Pandey et al. analyzed the moderate and severe lower respiratory tract infection (
II and III/iv ari).
In an expanded study conducted by Campbell et al in the Gambia on the same area, 50% of children with symptoms and signs of lower respiratory disease had radiology confirmed pneumonia.
56 The remaining studies were based on clinical diagnosis or on who's recommendation in the hospital setting or oral autopsy in children with pneumonia, severe breather bronchitis, or Mao Zhiyan.
These outcome indicators often include children with more serious illnesses.
Exposure to household smoke pollution was also assessed using different methods.
In general, these studies examined the relationship between the outcome measures and cooking practices, such as the use of open-air wood fire compared to clean fuels such as kerosene, 57 behavioral practices, etc.
For example, the carriage on the mother's back when cooking 53555658-61—
Or a source. 62-
For example, 64 Pandey et al, 53, used the time the mother reported spent near the stove as an absolute exposure measure to explore the dose
The relationship between smoking exposure and the response of children's lower respiratory diseases (fig 3).
Only one study actually measured the level of pollutants, and only one study household measured the level of pollutants.
Figure 3 acute respiratory infection (ARI)
And exposure to biomass smoke in Nepal. (A)
According to the six-month data of about 250 babies in early 1984. (B)
According to the three-month data for the same population at the end of 1984 and early 1985, there were separate teams that diagnosed ARI and identified smoke exposure.
The trend of moderate and severe cases was significant in both studies.
Copied with the permission of Pandey and others.
53 air pollution studies in Kenya and Gambia have shown that due to the homogeneity of levels between households, conditions are not conducive to detecting the relationship between pollutant concentrations and lower respiratory diseases in children.
65 Collingset al, 57 however, in the families of 20 children with lower respiratory diseases and 20 children with upper respiratory diseases, significant levels of total granules were found during cooking
A study also explored the possibility of using carbon-oxygen hemoglobin as a smoke exposure marker, but proved unsatisfactory due to the difficulty of controlling the post-exposure time.
In addition to one of the eight studies of incidence that found significant associations, the rest were in Africa.
A non-dataAfrican study (Nepal53)
Consistent with the greater relative risk of more severe diseases, but the numbers are too small to rule out opportunities as an explanation.
Age-specific data provided in the Nepal study showed that the impact of infants was not greater than in the second year.
In a detailed analysis of the Gambia data, Armstrong and Campbell 56 found that the risk of pneumonia associated with smoking increased in girls but not in boys.
The authors argue that this difference is due to more female exposure than to biological differences between genders.
These studies take into account potential confounders in the design and analysis methods (tables 6 and 7).
Inadequate control of the mix factor may lead to excessive odds, as the use of open fire and biomass fuel is associated with ALRI's poverty and associated risk factors.
Other possible sources of bias include misclassification of exposure by recalling bias. Case-
Control studies are more likely to be affected by recall bias, although this bias may also occur in prospective studies when exposure data are collected to track disease occurrence.
For example, in the Kossove58 study of children in Natal Zulu, the reported smoking duration was very similar in cases and controls, although the proportion of women who reported smoking in children (
Determined by the questionnaire)
Much higher in the case. Bias in case-
A controlled study of different uses of health services may create bias if subjects using health services suffer from severe pediatric conditions but do not suffer from minor illnesses or preventive health care, there are also those who cook using unprocessed biomass fuels who have not taken any steps to avoid exposing young children to smoke.
In one of the cases
Controlled studies from Africa but other countries have shown that cases and controls have different breastfeeding patterns and socio-economic status. 57 In the case-
The control study of Kossove58 is not clear if the clinical controls are less sick.
This method of controlling the choice may introduce bias, if the child is exposed to more severe indoor air pollution, the caregiver is less likely to take the child to these services to prevent health care when the child is slightly uncomfortable or unwell, but like others, it is also very possible to bring children when they are seriously ill.
This will lead to severe exposure of children
The odds represented in the control group and bias were far away from unity.
This could be caused by the distance these families are from the clinic, the inability to pay for transportation, or other constraints associated with poverty.
In principle, this situation is very likely, because the families at the highest risk are also the families most likely to be poor, inconvenient to transport, etc.
In practice, since there is no direct study seeking care, it is difficult to assess whether this bias contributes to risk estimates in the cited study.
However, from the information on socio-economic conditions in the three studies, there seems to be no difference between the case and the control.
575862 Morris et al discussed the source of this bias, as there was some evidence in their study that the socio-economic environment (
Dirty floor, lack of tap water)
Poorer in cases.
However, it is reported that more than 90% of children born in the hospital catchment area have completed routine immunization, suggesting that a control sample from the well baby clinic may represent the population.
The Shahet al63 study provided limited information on the socio-economic environment of cases and controls and, in any case, no increased risk of smoking was reported.
Cerqueiro and others from Argentinian cities have matched five factors, including socio-economic status and place of residence.
Overall, this bias does not seem to matter in this group of cases
Although there is no specific information on the search for care, a controlled study remains a possible source of error.
Studies by Cerqueiro and others have found a large odds (9. 9, 95% CI 1. 8 to 31)
For hospital patients diagnosed with ALRI, compared to controls matched with socio-economic levels, nutritional status, and other factors, home heating is usually addressed only through multivariate analysis in other studies (table 5).
No pollution measurements were reported and no information was provided on the type of furnace and fuel involved.
Cook with gas (
Not Electricity)
There are also significant odds (2. 2, 95% CI 1. 2 to 3. 9).
Interestingly, these three studies found that studies with no significant association were the only ones that relied on questionnaires to determine which stove or fuel was used by the household, without additional information about the behavioral patterns of the family.
In Kerala, India, the measurement of exposure is about whether there is a "smoke-free" stove (with a flue)at home.
Unfortunately, however, such stoves in India do not actually reduce indoor air pollution levels.
66. this study in Brazil was conducted in a city with a low prevalence of wood cooking in households (6%). 64 The case-
A controlled study reported by Johnson and Aderele, Nigeria, found that the incidence of ALRI was not significantly associated with the reported type of domestic fuel, but did find that the type of fuel was closely related to mortality.
62. other studies in India on infant ARI in less than a year, 74 were not eligible for table 5 due to their broad definition of ALRI, some conflicting results have been found in urban slum communities where households use biomass fuels and other kerosene.
This may be due to the strong interference of large-scale urban outdoor pollution and local outdoor "neighborhood" pollution from the stove itself and other neighborhood sources.
Another study that did not meet the inclusion in Table 5 due to its inclusive case definition was a pre-selection of 650 randomly selected
14-year-old school-age child in Lucknow, India for 1-59 months.
5% of people were found to have respiratory diseases such as runny nose, cough, sore throat, difficulty breathing or breathing noise.
68 after adjustment according to age, weight, gender, income and type of house, use feces as cooking fuel (OR 2. 7, 95% CI 1. 4 to 5. 3)and crowding (OR 1. 2, 95% CI 1. 1 to 1. 4)
Related to one or more of these respiratory symptoms.
In this study, the location of the child during cooking, ETS and cooking with coal, kerosene or wood was not related to respiratory symptoms.
In the six-month prospective study previously discussed for 650 1-53-month children in the same region, a somewhat different result was obtained.
Through home visits every two weeks, it was found that outdoor TSP measurements were significantly associated with symptoms and/or duration of symptoms.
Cook with any solid fuel after 75 multivariate analysis (ORs 1. 3 (wood); 1. 6 (coal); 1. 5 (dung))or kerosene (OR 1. 4)
Stay indoors while cooking (OR 2. 0, 95% CI 1. 7 to 2. 4)
Also significantly related.
The incidence of "possible pneumonia" is also determined by cough and difficulty breathing, only found to be closely related to the use of fecal fuel (OR 1. 01, 95% CI 1. 00 to 1. 02).
A study of 658 children aged 0-6 in Jakarta found that, despite multivariate analysis, the incidence of respiratory symptoms was associated with evidence that garbage was not collected around the house (OR 1. 6)
, They have nothing to do with the type of cooking fuel used.
76. The author speculated that the sample size of households using wood burning furnaces (not given)
Too small to find the effect, the effect of garbage may be caused by smoke generated by frequent combustion.
A large national household survey in India found that there is a significant statistical relationship (OR 1. 3)
Between reported household biomass fuel use and reported respiratory infections in children under the age of the previous Friday.
77. since the investigation did not distinguish cases by ALRI, URI or severity, however, this may not be a good predictor of the risk of a serious life-threatening ALRI.
In Nigeria, a study by ALRI showed a link between exposure to household biomass pollution and pneumonia mortality.
62 although a case
A controlled study in the same hospital did not reveal the relationship between the type of cooking fuel and ALRI's hospital stay, and ALRI's children came from wood-burning families, who were 12 years old. 2 times (p