EDUCATION: URBANMAAP

Research Projects: Asthma

Introduction to UrbanMAAP Asthma Research Projects

Currently a comprehensive data set for asthma does not exist. Much of what is "known" about asthma has been determined from asthma mortality and hospitalization data that have been used as a proxy for asthma prevalence. There are several potential problems with these data sources namely the mortality and hospitalization data may be biased by socioeconomic differences in the availability of healthcare and therefore may over emphasize urban areas where the larger populations produce meaningful statistics. While these data sets may be biased, they nonetheless reveal a disturbing pattern of increases in asthma hospitalization and mortality despite advances in medical treatment.

The heightened awareness of the global asthma problem has led to a number of research/surveillance projects aimed at providing a more accurate picture of asthma and the factors that influence the incidence of asthma and are responsible for the dramatic increases in asthma over the past two decades. While there is no single accepted theory to explain the increase in asthma, the fact that it is a global problem suggests to us that it is environmental in nature. Several studies have rejected the idea that pollution is responsible. Two of the most frequently cited arguments against pollution are: (1) that the atmosphere has gotten cleaner over the past two decades and (2) studies comparing the prevalence of asthma in eastern and western European countries have found that asthma rates are lower in the more polluted eastern countries. However, when we look at the individual pollutants we find that while on a whole the atmosphere has gotten cleaner (e.g., lower levels of sulfur dioxide (SO₂), carbon monoxide (CO) and lower levels of large particulates (PM10)), levels of nitrogen oxides have increased. Coupled with this increase in the levels of nitrogen oxides has been a change in the chemical composition of the atmospheric aerosols, since there is less sulfur dioxide to produce sulfate aerosols, the nitrate fraction of the aerosols has increased. We believe that nitrogen oxides and nitrate aerosols are playing a role in the increase in asthma. But where do we go from here?

While it is possible to find relationships between asthma and a variety of factors, it is not always possible to determine the process through which the factor influences asthma. For example, several studies have found a relationship between asthma and the concentration of aerosols in the air. So while asthma is positively correlated with particulate pollution the physiological mechanism through which the aerosols cause asthma has not been identified. While such investigations are beyond the scope of UrbanMAAP projects we note that several studies have now been published that show that nitrogen oxides can trigger asthma. In addition, nitrogen oxides lower the threshold for allergic reactions. Thus, the concentration of allergen that is needed to trigger an allergic reaction is lower in the presence of increasing amounts of nitrogen oxides. There are additional physiological studies that have measured respiration and have found excess nitrogen oxides and lower pH values in the exhalations of asthmatics. These studies strongly suggest that nitrogen oxides may be playing a role. So what next?

This is where UrbanMAAP comes in. In this project we are looking for a relationship between asthma and pollution (namely nitrogen oxides and aerosols). If our hypothesis is correct then we would expect to see higher levels of asthma associated with higher levels of nitrogen oxides. While on the surface that seems to be a straightforward research task there are several confounding factors. First, there is the issue of what do we use as an asthma data set. Second, nitrogen oxide measurements are not available for all locations and certainly not available on the spatial scale that we need them. Third, nitrogen oxides are chemically reactive in the atmosphere.

Starting with the asthma data, before we began UrbanMAAP we analyzed the mortality data for the New York City metropolitan area (shown below). Consistent with the hospitalization data we found higher amounts of asthma in the Bronx and lower amounts of asthma in Queens. We also found that the death rate is increasing faster in the Bronx than the statewide average. In fact, the Bronx, Manhattan, and Brooklyn all have mortality rates considerably higher than the state average, so is asthma an urban problem? At the same time we found a relationship between the number of asthma hospitalizations and the nitrate fraction of inhalable particulates. This relationship predicts a higher prevalence of asthma in Manhattan than that based on hospitalization or mortality data.

Naturally, we thought that something had to be wrong with our relationship between asthma and nitrate fraction. But, is it possible that something is wrong with using mortality and/or hospitalization data as a proxy for asthma prevalence?

To address this question, we created the first UrbanMAAP survey. This survey was analyzed to determine the prevalence of asthma in the New York metropolitan area. Based on the survey data, we found that the prevalence of asthma is actually higher in Manhattan than it is in the Bronx. But when it comes to asthma burden (defined to be the number of asthma attacks divided by the number of people with asthma) we found the asthma burden to be higher in the Bronx than in Manhattan. This finding suggests that there are regional differences in asthma management and could be used by policy makers to develop better asthma management plans.

What then is responsible for the differences between the mortality and hospitalization data and the UrbanMAAP survey? For starters, we hypothesized that the hospitalization data may contain a socioeconomic bias. If, for example, more people in Manhattan visit their own doctor for asthma treatment and have their asthma effectively managed then they would not be going to the hospital for treatment. So, we added questions to the UrbanMAAP Asthma Survey to provide some insights into this question. To get at availability of medical care and type of medical care we asked the respondents to tell us where they are most likely to go for treatment when they have an asthma attack. While to get some information about how socioeconomic factors influence asthma statistics we asked the respondents to tell us their zip code and the cost of their school lunch. In the New York public schools subsidized lunches are available. This past summer, student participants analyzed the survey data and compared the type of lunch payment with zipcode level income information (available from the census data) and found a relationship between income and type of lunch payment. In addition, the students found a relation between income and type of medical care with higher income respondents more likely to have their asthma treated by a personal physician than lower income respondents. Finally, the survey data support the higher prevalence of asthma in Manhattan found in the analysis of our first survey and suggest that the hospitalization data underestimate asthma prevalence in Manhattan because a greater percentage of the people in Manhattan visit a personal physician for treatment than in the Bronx.

This is where you come in, while we have already been able to answer a number of interesting questions using the UrbanMAAP survey data, there are many more questions that remain to be answered.

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