Reunion Island is a French overseas department characterized by a tropical climate with 2 distinct seasons. While the prevalence of asthma among adults in Reunion Island is close to that in mainland France, mortality and hospitalization rates are twice as high. To date, however, no epidemiological studies have evaluated the influence of environmental factors in asthma exacerbations in Reunion Island.

From January 2010 to June 2013, 1157 residents of Saint-Denis visited the emergency rooms of the Centre hospitalier universitaire site Nord de Saint-Denis for asthma. After exclusion of children under the age of 3, 864 visits were analyzed. These were correlated with the following daily factors: pollens and molds, meteorological parameters (temperature, precipitation levels, humidity and relative humidity levels, wind), pollutants (sulfur dioxide (SO₂), nitrogen oxide (NO_x), and the fine particles PM₁₀ and PM_2.5), and the influenza virus. The correlation between these factors was evaluated using the DLNM and GO-GARCH models.

Of the 864 analyzed visits, 532 were by pediatric patients (aged 3 to 16 years) and 332 by adult patients (aged over 16 years). In adults, pollens positively correlated with asthma exacerbations were Urticaceae, Oleaceae, Moraceae, and Chenopodiaceae. In children, these were Urticaceae, Oleaceae, Poaceae, and Myrtaceae. Molds positively correlated with asthma exacerbations in adults were ascospores and basidiospores. Only basidiospores were positively correlated with exacerbations in children. Temperature was positively correlated with exacerbations in both adults and children. The pollutants PM₁₀ and NO_x were positively correlated with exacerbations in children. Influenza epidemics were strongly correlated with exacerbations in both adults and children.

Our analysis shows that in Reunion Island, asthma is exacerbated by pollens (Urticaceae, Oleaceae, Moraceae, Chenopodiaceae in adults; Urticaceae, Oleaceae, Poaceae, Myrtaceae in children), molds (ascospores and basidiospores in adults; basidiospores in children), temperature, influenza, and the pollutants PM₁₀ and NO_x (in children).