Saharan Dust and Pediatric Asthma : A Multinational, Multiyear Assessment in the Caribbean
Nichols, Naomi Ty Asha
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Background: The annual seasonal intrusion of Saharan Dust to the Caribbean has been linked with asthma, a complex disease and a major cause of morbidity in the Caribbean and around the world. This first multinational, multiyear epidemiologic study of Saharan Dust in the Caribbean examines the risk of asthma emergency room (ER) visits on Saharan dust days (SDD). Saharan dust is the main source of aerosol pollution in the Caribbean, and its composition is determined by the mineral dust source and the interactions with pollutants picked up during transport. These include anthropogenic aerosols such as black carbon (BC) from biomass burning in sub-Saharan Africa and South America. Methods: We examined the associations between SDD and asthma ER visits on four islands from January 2015 to December 2017 among children between the ages of 1 and 15 years old. These islands extend from 15.50 N, (Dominica) to 120 N (Grenada), bracketing St. Lucia (13.30 N) and St. Vincent (130 N). Particulate exposure was estimated using bias-corrected MERRA-2 satellite based derived PM2.5 and PM10 (particulate matter <2.5 µm and <10 µm respectively) data and the total black and organic carbon components (TCC) thereof. SDDs, as described in a previous Caribbean paper, were defined by days that occurred only during the dust season with PM10 exceeding 35 µg/m3 (SDD10) or PM2.5 exceeding 11µg/m3 (SDD2.5). Multivariate analyses were performed using time-stratified (“filtered”) conditional (case-crossover) Poisson regression techniques with distributed lags constrained via spline smoothing. The primary analysis included all ER visits and secondary analyses were performed on sub-groups by year and by island. Results: Records used in this study describe a total of 6353 asthma ER visits. There was a 9% (95% CI: 1% - 18%) increased average (over lags 0-6 days) regional (over all islands) risk of asthma ER visits on SDD2.5 but no significant association with SDD10. Results by individual year and island were variable. There was an increased average regional risk in 2016 with exposure to SDD2.5 (12%, CI: 3-22%). Among the islands, Grenada had an increased average risk with SDD2.5 (13%, CI: 4 - 24%), and similarly St. Lucia (11%, CI:1% - 22%). Grenada also had the highest TCC among the islands and St. Lucia the highest levels of local urban anthropogenic PM10. Conclusion: SDDs defined by high PM2.5 concentrations, were positively associated with pediatric asthma ER visits. The findings suggest that, in the Caribbean, susceptible pediatric asthma patients are at an increased risk from Saharan dust, but its association is complex. Differing results between individual islands and years may be partially attributable to differing anthropogenic sources and other confounding factors including seasonal influenza infections.