Asthma is a respiratory disease characterized by bronchial hyperresponsiveness, bronchial constriction, airway inflammation and recurrent airflow obstruction. It is accompanied by respiratory symptoms such as wheezing, dyspnea, coughing, and chest tightness. The development of asthma is multifactorial, and is currently poorly understood. Among the risk factors mentioned in the literature as potential causes of asthma are genetic predisposition, inheritance of atopy, and environmental factors such as allergen exposure, environmental tobacco smoke, socioeconomic status, nutrition, low birth weight, history of infections, and ambient levels of air pollution.1
The constriction of the airways in asthmatics is triggered by histamines, which are produced by the immune system as a reaction to foreign substances. Histamines act to bring more blood and lymph fluid to the site where a foreign substance is found in order for immune cells to fight these substances and for blood to carry them away. Histamines are released by mast cells, which store a variety of inflammatory mediators, and this process is triggered by their immunoglobulin E (IgE) proteins which are in turn activated by the molecules to which they have been sensitized. The result is intermittent episodes of wheezing, coughing and breathlessness in the afflicted individuals. In severe cases, asthma attacks can result in death.2
Asthma in Bronx County
Bronx County has some of the highest rates of asthma in the United States. Rates of death from asthma in the Bronx are about three times higher than the national average. Hospitalization rates are about five times higher. In some neighborhoods in the Bronx it is estimated that 20% of the children have asthma.3 Within New York City the disparity in asthma hospitalization rates is very pronounced. According to a study, hospitalization rates for asthma in Bronx County and East Harlem are 21 times higher than those of affluent parts of the city.4
As the following graph shows, Bronx County has the highest pediatric
asthma (children 0-4 years) hospitalization rates in the New York area. New
York County (Manhattan) has the second highest rate. Richmond County (Staten
Island) and Upstate New York, which according to the definition used by the
NYS Department of Health includes all of New York State except New York City,
have pediatric asthma hospitalization rates that are significantly lower than
those of the other counties included in the graph.5
The association between air pollution and asthma remains poorly understood. Since exposure is always to a mix of pollutants it is difficult for epidemiological studies to define causal agents in the mix. Asthma has been linked to a number of pollutants. The most commonly studied are the criteria pollutants which are regulated in the United States by the Clean Air Act. The criteria pollutants are carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), particulate matter (PM10 and PM2.5) and lead (Pb). Of these, lead is not considered relevant to the development or exacerbation of asthma. One of the ways air pollutants may affect asthmatics is by promoting airway sensitization to airborne allergens in predisposed subjects. Laboratory studies suggest that pollutants can attach themselves to allergens such as pollen and increase their allergenic potential. Pollutants can induce airway inflammation and they can also facilitate the access of inhaled allergens to the cells of the immune system.6
Recent attention has been focused on diesel exhaust particles. This is an important component of fine particulate matter (PM2.5). These particles, which have a diameter of 2.5 microns or less, are considered to be particularly dangerous to long-term human health because they are able to penetrate deep into the respiratory system and the lungs. Diesel exhaust is of particular concern to residents of the South Bronx because a large number of diesel trucks drive to and from waste transfer stations and other commercial destinations in the area.
For more information on this topic, see Chapter 5: Asthma and Air
Pollution: A Literature Review, of the Phase I Report. *Phase I Report.