Epidemiological study on a controlled group of allergic patients on Gran Canaria impacted by Saharan dust

Abstract

Gran Canaria is located off the west coast of North Africa, and close to the Sahara desert, a major source of natural mineral particles (NMP). The island is frequently impacted by Saharan dust (about 30% of the time each year, at an average duration of 3-5 days per event). The annual deposition rate is 15.6 g/m2, and the mean grain-size is 15 µm, with about 20% being <5 µm. The Gran Canaria population in 2011 was 850,391, plus 89,824 transient tourists. In addition, shipping (22,220,273 metric tons handled in 2011) and air traffic (11,271 flights in 2011) are both large contributors to air pollution. Electricity and desalinated, potable water are produced by diesel fuel power plants. In the same year there were 811,837 registered motor vehicles on the island. In urban parts of the island, people are inhaling the local anthropogenic pollution, together with NMP during Saharan dust events. We conducted an epidemiological survey together with an air quality study in 2011, the latter being the quarterly monitoring of a group of 24 adult outpatients at a hospital (12 with mild asthma and rhinitis, and 12 with moderate to severe asthma and rhinitis). During each visit, a full medical examination was performed on each patient, including simple spirometry and bronchial inflammation tests (measurement of exhaled nitric oxide). Patients also completed validated standard and linguistic tests (quality of life in rhinitis and asthma, asthma control test and overall health status). Similarly, symptoms were recorded on a card by the patients at home, on a daily basis, including ocular, nasal and bronchial conditions and lung function (Peak Flow registration). The medications were reviewed in order to assess the clinical and functional status of each patient. Over the same period, aerosol samples were collected on a weekly schedule, with Airmetrics MiniVol® filter samplers (5 l/min). The PM2.5 filters were analyzed for elemental composition, water soluble ions, carbon, mineralogical content, and individual particle morphology by Scanning Electron Microscopy. Analysis of variance (ANOVA) and Spearman correlation coefficients were applied to the air quality and clinical data. No statistically significant relationship between the pulmonary conditions, medication and elevated dust levels could be established from our data set.