Interaction between ambient pollutant exposure, CD14 (-159) polymorphism and respiratory outcomes among children in Kwazulu-Natal, Durban

Ambient air pollution and non-communicable respiratory illness in sub-Saharan Africa: a systematic review of the literature

INTRODUCTION

Aerosol pollutants are known to raise the risk of development of non-communicable respiratory diseases (NCRDs) such as asthma, chronic bronchitis, chronic obstructive pulmonary disease, and allergic rhinitis. Sub-Saharan Africa's rapid pace of urbanization, economic expansion, and population growth raise concerns of increasing incidence of NCRDs. This research characterizes the state of research on pollution and NCRDs in the 46 countries of Sub-Saharan Africa (SSA). This research systematically reviewed the literature on studies of asthma; chronic bronchitis; allergic rhinitis; and air pollutants such as particulate matter, ozone, NOx, and sulfuric oxide.

METHODS

We searched three major databases (PubMed, Web of Science, and Scopus) using the key words "asthma", "chronic bronchitis", "allergic rhinitis", and "COPD" with "carbon monoxide (CO)", "sulfuric oxide (SO)", "ozone (O3)", "nitrogen dioxide (NO2)", and "particulate matter (PM)", restricting the search to the 46 countries that comprise SSA. Only papers published in scholarly journals with a defined health outcome in individuals and which tested associations with explicitly measured or modelled air exposures were considered for inclusion. All candidate papers were entered into a database for review.

RESULTS

We found a total of 362 unique research papers in the initial search of the three databases. Among these, 14 met the inclusion criteria. These papers comprised studies from just five countries. Nine papers were from South Africa; two from Malawi; and one each from Ghana, Namibia, and Nigeria. Most studies were cross-sectional. Exposures to ambient air pollutants were measured using spectrometry and chromatography. Some studies created composite measures of air pollution using a range of data layers. NCRD outcomes were measured by self-reported health status and measures of lung function (spirometry). Populations of interest were primarily schoolchildren, though a few studies focused on secondary school students and adults.

CONCLUSIONS

The paucity of research on NCRDs and ambient air pollutant exposures is pronounced within the African continent. While capacity to measure air quality in SSA is high, studies targeting NCRDs should work to draw attention to questions of outdoor air pollution and health. As the climate changes and SSA economies expand and countries urbanize, these questions will become increasingly important.

Environmental Health Research in Africa: Important Progress and Promising Opportunities

The World Health Organization in 2016 estimated that over 20% of the global disease burden and deaths were attributed to modifiable environmental factors. However, data clearly characterizing the impact of environmental exposures and health endpoints in African populations is limited. To describe recent progress and identify important research gaps, we reviewed literature on environmental health research in African populations over the last decade, as well as research incorporating both genomic and environmental factors. We queried PubMed for peer-reviewed research articles, reviews, or books examining environmental exposures and health outcomes in human populations in Africa. Searches utilized medical subheading (MeSH) terms for environmental exposure categories listed in the March 2018 US National Report on Human Exposure to Environmental Chemicals, which includes chemicals with worldwide distributions. Our search strategy retrieved 540 relevant publications, with studies evaluating health impacts of ambient air pollution (n=105), indoor air pollution (n = 166), heavy metals (n = 130), pesticides (n = 95), dietary mold (n = 61), indoor mold (n = 9), per- and polyfluoroalkyl substances (PFASs, n = 0), electronic waste (n = 9), environmental phenols (n = 4), flame retardants (n = 8), and phthalates (n = 3), where publications could belong to more than one exposure category. Only 23 publications characterized both environmental and genomic risk factors. Cardiovascular and respiratory health endpoints impacted by air pollution were comparable to observations in other countries. Air pollution exposures unique to Africa and some other resource limited settings were dust and specific occupational exposures. Literature describing harmful health effects of metals, pesticides, and dietary mold represented a context unique to Africa. Studies of exposures to phthalates, PFASs, phenols, and flame retardants were very limited. These results underscore the need for further focus on current and emerging environmental and chemical health risks as well as better integration of genomic and environmental factors in African research studies. Environmental exposures with distinct routes of exposure, unique co-exposures and co-morbidities, combined with the extensive genomic diversity in Africa may lead to the identification of novel mechanisms underlying complex disease and promising potential for translation to global public health.

Ambient air pollution and health in Sub-Saharan Africa: Current evidence, perspectives and a call to action

BACKGROUND

People from low- and middle-income countries are disproportionately affected by the global burden of adverse health effects caused by ambient air pollution (AAP). However, data from Sub-Saharan Africa (SSA) are still scarce. We systematically reviewed the literature to describe the existing knowledge on AAP and health outcomes in SSA.

METHODS

We searched PubMed, Medline-OVID, EMBASE and Scopus databases to identify studies of AAP and health outcomes published up to November 15, 2017. We used a systematic review approach to critically analyze and summarize levels of outdoor air pollutants, and data on health effects associated with AAP. We excluded occupational and indoor exposure studies.

RESULTS

We identified 60 articles, with 37 only describing levels of AAP and 23 assessing the association between air pollution and health outcomes. Most studies (75%) addressing the relation between AAP and disease were cross-sectional. In general, exposure data were only obtained for selected cities in the framework of temporary international collaborative research initiatives without structural long-term continuation. Measurements of AAP revealed 10-20 fold higher levels than WHO standards. Of the 23 studies reporting health effects, 14 originated from South Africa, and most countries within SSA contributed no data at all. No studies, except from South Africa, were based on reliable morbidity or mortality statistics at regional or country level. The majority of studies investigated self-reported respiratory symptoms. Children and the elderly were found to be more susceptible to AAP.

CONCLUSION

AAP and its negative health effects have been understudied in SSA compared with other continents. The limited direct measurements of air pollutants indicate that AAP in SAA cities is high compared with international standards. Efforts are needed to monitor AAP in African cities, to identify its main sources, and to reduce adverse health effects by enforcing legislation.

Chemical and Biological Components of Urban Aerosols in Africa: Current Status and Knowledge Gaps

Aerosolized particulate matter (PM) is a complex mixture that has been recognized as the greatest cause of premature human mortality in low- and middle-income countries. Its toxicity arises largely from its chemical and biological components. These include polycyclic aromatic hydrocarbons (PAHs) and their nitro-derivatives (NPAHs) as well as microorganisms. In Africa, fossil fuel combustion and biomass burning in urban settings are the major sources of human exposure to PM, yet data on the role of aerosols in disease association in Africa remains scarce. This review is the first to examine studies conducted in Africa on both PAHs/NPAHs and airborne microorganisms associated with PM. These studies demonstrate that PM exposure in Africa exceeds World Health Organization (WHO) safety limits and carcinogenic PAHs/NPAHs and pathogenic microorganisms are the major components of PM aerosols. The health impacts of PAHs/NPAHs and airborne microbial loadings in PM are reviewed. This will be important for future epidemiological evaluations and may contribute to the development of effective management strategies to improve ambient air quality in the African continent.

Alterations by Air Pollution in Inflammation and Metals in Pleural Effusion of Pneumonia Patients

Air pollution is known to increase the risk of pneumonia. However, the effects of air pollution on the pleural effusion of patients with pneumonia are unclear. The objective of this study was to investigate alterations in inflammatory–immune biomarkers by air pollution in patients with pneumonia by analyzing their pleural effusion. Patients who had undergone thoracentesis to drain their pleural effusion in a hospital were recruited for this study. Patients with pneumonia and those with congestive heart failure respectively served as the case and control groups. We observed that an increase of 1 ppb in one-year NO₂ was associated with a decrease of 0.105 ng/mL in cluster of differentiation 62 (CD62) (95% confidence interval (CI) = −0.085, −0.004, p < 0.05) in the pleural effusion. Furthermore, we observed that an increase in one−year 1 ppb of NO₂ was associated with a decrease of 0.026 ng/mL in molybdenum (Mo) (95% CI = −0.138, −0.020, p < 0.05). An increase in one-year 1 ppb of SO₂ was associated with a decrease of 0.531 ng/mL in zinc (95% CI = −0.164, −0.006, p < 0.05). Also, an increase in one-year 1 ppb of O₃ was associated with a decrease of 0.025 ng/mL in Mo (95% CI = −0.372, −0.053, p < 0.05). In conclusion, air pollution exposure, especially gaseous pollution, may be associated with the regulation of immune responses and changes in metal levels in the pleural effusion of pneumonia patients.

A Narrative Review on the Human Health Effects of Ambient Air Pollution in Sub-Saharan Africa: An Urgent Need for Health Effects Studies

An important aspect of the new sustainable development goals (SDGs) is a greater emphasis on reducing the health impacts from ambient air pollution in developing countries. Meanwhile, the burden of human disease attributable to ambient air pollution in sub-Saharan Africa is growing, yet estimates of its impact on the region are possibly underestimated due to a lack of air quality monitoring, a paucity of air pollution epidemiological studies, and important population vulnerabilities in the region. The lack of ambient air pollution epidemiologic data in sub-Saharan Africa is also an important global health disparity. Thousands of air pollution health effects studies have been conducted in Europe and North America, rather than in urban areas that have some of the highest measured air pollution levels in world, including urban areas in sub-Saharan Africa. In this paper, we provide a systematic and narrative review of the literature on ambient air pollution epidemiological studies that have been conducted in the region to date. Our review of the literature focuses on epidemiologic studies that measure air pollutants and relate air pollution measurements with various health outcomes. We highlight the gaps in ambient air pollution epidemiological studies conducted in different sub-regions of sub-Saharan Africa and provide methodological recommendations for future environmental epidemiology studies addressing ambient air pollution in the region.

Genetic Diversity of CD14 Promoter Gene Polymorphism (rs2569190) is Associated With Regulation of Malaria Parasitemia and Susceptibility to Plasmodium falciparum Infection

CD14 is a multifunctional receptor expressed on many cell types and has been shown to mediate immune response resulting in the activation of an inflammatory cascade, with polymorphism of its promoter (rs2569190) found to be associated with susceptibility to several diseases. In malaria infection, the CD14 gene demonstrated a pathogenic profile in regulating experimental cerebral malaria, with reports of elevated levels of soluble CD14 in serum of patients but no definitive conclusion. We present a detailed analysis of genetic diversity of CD14 promoter gene (snp −159 C/T; rs2519190) polymorphism between a malaria-infected group and uninfected controls and its association with clinical parameters of disease. Genomic DNA samples obtained from 106 Plasmodium falciparum malaria–infected patients and 277 uninfected controls were elucidated with a polymerase chain reaction-restriction fragment length polymorphism (RFLP) assay. Our results show a significant diversity (P = 3.32E−06) in the genotypic frequency (3.8% versus 22.4%) of the rs2569190 mutant variant between the malaria-infected group and controls, respectively. The mutant allele had the lowest frequency among the malaria-infected group demonstrating its necessity for infection. Mean parasitemia (parasites/μL of blood) was significantly regulated based on CD14 polymorphic profile (19 855 versus 37 041 versus 49 396 for homozygote mutants, heterozygotes, and homozygote wild type, respectively). Interestingly, we found no association between CD14 genetic variants with fever, age of patients, or anemia. How this affects disease severity between subregional and continental groups deserves further clarification, including extending these studies in a larger group and among severe and asymptomatic patients with malaria.