The adverse respiratory-system effects of pollution substances such as nitrogen dioxide, sulfur dioxide, ozone, diesel exhaust, and diesel exhaust particles (DEPs) are well documented (Dockery, 2001; Haahtela et al., 1991; Koenig, 1999; Loh, Sugerman-Brozan, Wiggins, Noiles, & Archibald, 2002; Pandya, Solomon, Kinner, & Balmes, 2002; Takenaka, Zhang, Diaz-Sanchez, & Saxon, 1995; Wong et al., 1999). A growing body of epidemiological evidence links current increases in morbidity from respiratory illnesses to air pollutants (Briggs et al., 1999; Donaldson, Gilmour, & MacNee, 2000; Edwards, Walters, & Griffiths, 1994; Ishizaki, Koizumi, Ikermori, Ishiyama, & Kushibiki, 1987; Lin, M., Chen, Burnett, Villeneuve, & Krewski, 2002; NILU, 1991; Norris et al., 1999; Schwartz, 1993, 1994; Weiland, Mundt, Ruckmann, & Keil, 1994; Wijst et al., 1993). Data linking air pollution to increases in asthma prevalence, however, are of limited availablity (Koenig, 1999).
Asthma is a chronic inflammatory disease characterized by episodes of reversible airflow obstruction and hyper-responsiveness to triggers, including air pollutants. Common symptoms of an attack include coughing, wheezing, shortness of breath, and chest tightness. Recent studies have reported an increase in asthma diagnosis in the past two decades among children and adults in the United States (Centers for Disease Control [CDC], 1998; Crain et al., 1994; National Institute of Allergy and Infectious Diseases [NIAID], 2001). According to NIAID (2001), asthma is a growing health problem in the United States, particularly among inner-city African-American and Latino populations.
Components of traffic-related pollutants, including particulates and ozone, have been shown to induce lung inflammation (Schwartz, 1993, 1994). Little information, however, is available at the subnational level regarding the health impacts of traffic-related pollution along the North American Free Trade Agreement (NAFTA) corridors. A few studies in the Northeastern United States have attempted to analyze the association between traffic-related pollution and asthma (Lwebuga-Mukasa & Dunn-Georgiou, 2002; Lwebuga-Mukasa, Wojcik, Dunn-Georgiou, & Johnson, 2002; Lin, Munsie, Hwanga, Fitzgerald, & Cayo, 2002). A recently completed 10-year study conducted by Lwebuga-Mukasa, Oyana, Thenappan, & Ayirookuzhi (2002) at a U.S.-Canada border crossing reported a positive association between increased commercial traffic volume and increased utilization of asthma health care. When there was a sudden drop in total crossborder traffic, following the World Trade Center tragedy of September 11, 2001, an associated decrease in the utilization of health care for all respiratory diseases occurred in the subsequent several weeks, with recovery to levels comparable to those of 2000 occurring with a rebound in traffic (Lwebuga-Mukasa, Ayirookuzhi, & Hyland, 2002). Furthermore, two cross-sectional house-to-house surveys conducted six years apart found that Buffalo communities in close proximity to the NAFTA corridor have an increased prevalence of asthma not explained by the usual personal or household factors (Lwebuga-Mukasa, Johnson, & Oyana, 2002; Lwebuga-Mukasa, Wojcik, et al., 2002). Geographically supported relationships between sources of pollution and use of health care have not, however, been fully explored. Identification of geographic patterns and distributions may contribute to better spatial and temporal characterization of respiratory diseases and thus contribute to better preventive and mitigation measures.
Residents living in close proximity to the Peace Bridge Complex and major roadways have complained of respiratory illnesses (Peace Bridge Review Commission, 1999). The major roadways are conduits of heavy trucks and buses, which serve the increasingly busy U.S.-Canada NAFTA corridor. The volume of commercial traffic passing along this trade corridor grew at a rate of 9 percent per year between 1991 and 1999 (Peace Bridge Review Commission, 1999). While infrastructure development has been emphasized, little information is available on the health impacts of traffic-related pollution. Previous studies have reported that high levels of vehicle emissions are associated with cardiopulmonary morbidity and mortality (Dockery, 2001; Dockery et al., 1993; Schwartz, 1996).
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The current study was motivated by two key interests: First, the authors wanted to investigate the spatial distributions of asthma cases in relation to major traffic corridors and the Peace Bridge Complex, and assess possible contributions of other U.S. Environmental Protection Agency (U.S. EPA)-identified pollution release sources in the study area. Second, the authors wanted to evaluate utilization of health care in the communities surrounding the city of Buffalo as previously reported (Lwebuga-Mukasa, Oyana, Thenappan, & Ayirookuzhi, 2002) in order to gain a broader perspective of the problem. The study evaluates five questions:
Is utilization of health care different at certain different distances from sources of pollution and major roadways?
Is utilization of health care different at certain different distances from major hospitals?
Are asthma cases clustered in certain locations--for example, in relation to health care facilities or pollution sources?
Where is asthma risk significantly elevated in the study area?
Does proximity to a pollution site increase the risk of having asthma?
Materials and Methods
Study Area and Population
The study area, as shown in Figure 1, comprised 28 zip codes located in Erie County, New York. The study area included the city of Buffalo and its major first-ring suburbs to the north and northeast (Tonawanda, Amherst, Kenmore, and Cheektowaga). Health care needs are primarily served by six major hospitals (Figure 1). According to the 2000 U.S. Census, the population of the study area was 544,269 (U.S. Census Bureau, 2000). In 1990, the study area had a total population of 609,992 (U.S. Census Bureau, 1990); the difference implies a decrease of 5.32 percent. According to the 2000 U.S. Census, the race/ethnic composition of the study area is 71.5 percent Caucasian, 21 percent African-American, 5 percent Latino/Hipansic, 2 percent Asian, and below 0.5 percent others. Of the 544,269 people, 47.1 percent were males and 52.9 percent were females. Approximately 24 percent of the population were between 1 and 17 years of age, 38 percent were between 18 and 44 years, 21 percent were between 45 and 64 years, and 17 percent were 65 years of age or older.
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Four data categories were analyzed in this study:
emergency room visits for asthma, 1999-2001;
hospital discharges for asthma, 1991-1996;
hospitalization and outpatient visits for asthma, 1995-2000; and
suspected sources of pollution sites derived from U.S. EPA databases.
The Kaleida Health System, the largest health system in Western New York (comprising Buffalo General Hospital, Millard Fillmore Hospitals [Gates and Suburban], DeGraff Memorial Hospital, and Children's Hospital of Buffalo), maintains automated relational databases of inpatient and outpatient records, which is updated regularly. The functions of these databases require a high level of accuracy; they are used, for instance, for billing and recovering patients' benefits from insurance companies. In-house data quality standards are based on international classification of diseases and metadata standards. Individual information contained in these databases permits the identification of individual cases that may involve multiple visits, which eliminates the duplication of records. The authors' experience with these databases, however, indicates that incomplete information collected from some patients constitutes about 10 percent of the information (including incorrect birthdays, spelling mistakes, and incorrect patient residential addresses), which can render some records redundant. This characterization applies to both databases (Emergency Room Data, 1999-2001, and Hospitalization and Outpatient Visits for Asthma, 1995-2000) that are discussed later.
A database of hospital discharges for asthma (1991-1996) is maintained by the Statewide Planning and Research Cooperative System (SPARCS) of the New York State Department of Health. The SPARCS database is of high quality and contains hospital discharge data from the whole of New York State, excluding psychiatric and federal hospitals. Geographical information from this database is available only at zip code level. The databases are described in detail below.
Emergency Room Data, 1999-2001
The emergency room (ER) data are based on electronic records of patients kept by Buffalo General Hospital, a division of the Kaleida Health System, between November 1999 and April 2001. The records contain the patients' dates of birth and admission, and their place of residence. Using the ER data, the authors were able to analyze the number of visits per patient, the period when the visits were made, and the distances between the patients' place of residence and the hospital. Distance analysis was performed for case address locations and Buffalo General Hospital. The spatial relationships enabled the characterization of relationships between case address locations, hospitals, hazardous sites, the Peace Bridge Complex, and major roadways. The ER data had certain limitations. They did not provide personal information on living conditions, the reasons patients frequented the emergency room, or the reasons they preferred certain health care facilities to others.
Hospital Discharges for Asthma, 1991-1996
Hospital discharges for asthma were obtained from the Statewide Planning and Research Cooperative System (SPARCS) data files in the New York State Department of Health Bureau of Biometrics (NYSDOHBB) database. The data files contained records for all patients...