Understanding the impact of air quality and weather conditions on respiratory health in Miami Dade and Broward Counties in South Florida

The impact of changing weather and air quality conditions on cardio-respiratory diseases is very important. To global climate changes, and the overwhelming migration from rural to urban environments that are affecting the quality of life in many places we should add the increase in health treatments and services. Never as before, preventive medicine has become so important. This analysis may help general health practitioners to anticipate increases in consultation and better manage resources. Epidemiological as well as biometeorology studies have documented the existence of exacerbating factors for asthma different from the typical allergens. Economic conditions, educational backgrounds, stress, diets, along with weather and air quality conditions appear to compete and complement the allergen hypothesis. Motivated by these facts and aimed at understanding the inner working of asthma, time series of Emergency Department (ED) visits due to asthma in Miami Dade and Broward Counties were provided by the Florida Asthma Coalition for six years (2005-2011) with daily temporal resolution. They show a peak of attendance between the months of November and January and a dip between the months of April and June every year, with an increase (decrease) about 30 % above (below) the mean number of visits per day during this period. Week-ends appear to be the most common time for ED visits, leading us to think about the influence of the exposition time to pollutants as well as possible lagging effects. Besides that, a spatial analysis of cases revealed that the proximity to highways is playing a role as well as the socio-economic status of people living in these areas. The time series of weather parameters (Temperature, Humidity, Wind Speed and direction, and Pressure) obtained from the Weatherbug mesonet in South Florida, surface ozone, and particulate matter obtained from EPA registered stations are compared and correlated with the number of ED visits due to asthma. Moderate to slightly strong correlation regimes are documented and discussed. Different lagging effects were found for Temperature, Humidity, Ozone and Particulate Matter which were estimated from the dependence of correlation coefficients and the degree of lagging. Lagging effects were analyzed up to seven days previous to ED visit. A General Additive Model (GAM) for Multilinear regression (MLR) was implemented based on the most sensitive lags. It is noteworthy that large levels of allergens and surface ozone tend to occur in spring and early summer due to the release of pollens, the end of the dry season which produces many wild-fires and the sun activated photolysis. Thus a question arises, what are the causes of this peak of asthma ED visits in winter? One of the most accepted molecular mechanisms leading to asthma attacks is the asymmetry in the helper T cells, in favor of the Th2 system instead of the Th1 controlled by regulatory T cells and an army of cytokines, B cells, Eosinophils, and several molecular factors. This immune response regulates the amount of mucus secreted within the airways, as well as the inflammatory process and the airway remodeling. However, endocrine disorders might also trigger asthma attacks under certain circumstances through the neuro-endocrine axis via the hypothalamic-pituitary-adrenal axis (HPAA). The later is responsible for the homeostatic control of temperature, heat exchange, and level of stress the organism may handle. Asthma appears to be a systemic disease triggered by different signaling pathways, which in turn seem to be associated with different combinations of environmental conditions. In this formulation, adverse environmental conditions are translated into stress variables such that a unifying picture may emerge. It is well known from meteorology that clear winter skies combined with low temperatures may produce temperature inversions and shallow boundary layers effects. This combination may inhibit the atmospheric mixing both vertically (convection) and horizontally (advection) and the concentration of pollutants near the surface increases. Persistent low temperatures and dry conditions together are factor stimulating molds and viruses spreading, which combined with moderate levels of ozone appears as the primary triggering mechanisms. Human responses to different environmental conditions are better described appealing to thermodynamic exchange leading to thermal homeostasis. This principle allows us to consider relative thermal and oxidative stress indexes which might help in predicting possible responses to adverse weather and air quality conditions. Relative indexes appear more suitable when data obtained from different geographical and climatic zones are contrasted each other. The cold weather stress and the physiological elasticity seem to be the most important triggers during the immune response in asthma episodes and might serve as predictors within a multiple regression model.