A Procedure for Detecting Childhood Cancer Clusters near Hazardous Waste Sites in Florida
Kearney, Greg, Journal of Environmental Health
For obvious reasons, a childhood cancer cluster located near a hazardous waste site is a serious public health concern. Despite extensive studies conducted over the past 20 years, little supporting evidence has been found to suggest an association, and the etiology of childhood cancers remains relatively unknown (Caldwell, 1990). Nevertheless, the perception of living near a hazardous waste site can raise fear and concerns. According to a Princeton survey of 801 registered voters in Florida, 89 percent felt that environmental factors such as pollution and toxic wastes played a significant role in causing diseases. Approximately 34 percent of parent voters with young children felt that childhood cancers such as leukemia were linked to environmental factors such as hazardous waste sites (Princeton Survey Research Associates, 2000). In addition, cluster inquiries usually involve local or state public health offices and require them to respond. Researchers at the Johns Hopkins Bloomberg School of Public Health found that 95 percent of state health departments surveyed (N = 37) reported having a cancer cluster investigation or inquiry. Of the states included in the survey, 81 percent reported brain cancer as the most common type of cancer cluster inquiry followed by leukemias, lymphomas, or both (72 percent) (Juzych et al., 2007).
To explore the issue of cancer clusters near hazardous waste sites, the author used a geographic information system (GIS) and spatial-scan statistical software, SaTScan (Version 6.0) to spatially and temporally detect the geographical location of childhood cancer clusters near U.S. Environmental Protection Agency (U.S. EPA) National Priority List (NPL) sites in Florida (U.S. EPA, n.d.). The NPL sites were chosen because they are considered the worst-of-the-worst hazardous sites in the nation.
SaTScan is a software tool developed by the National Cancer Institute for cluster detection and can be downloaded at http://www.satscan.org/. SaTScan can work by any of the following methods: a) evaluate reported spatial or space-time disease clusters and determine if they are statistically significant, b) test whether a disease is randomly distributed over space, time, or space-time, c) perform geographical surveillance of disease, d) test geographical areas of significantly high or low rates, and e) perform repeated time-periodic disease surveillance for the early detection of disease outbreaks (NCI, 2004). The program uses a circular window filter that scans over a map, smoothing out the data while analyzing for clusters. The circular windows are generated around geographical centroids, or central longitude/latitude coordinates of polygons projected on a map. Using this software, the author detected childhood cancer clusters and estimated their proximity to an NPL site using a geographic information system (GIS).
Cancer case records were identified from confidential data retrieved with Institutional Review Board (IRB) approval from the Florida Cancer Data System (FCDS) (FCDS, n.d.). The study period was January 1, 1990, through December 31, 1999. The case definition included any resident of Florida who was between 0 and 19 years of age at the time of diagnosis and who was diagnosed with a new primary cancer or reportable condition during the study period. The childhood cancer cases included those with a primary diagnosis of selected leukemias, lymphomas (not including Hodgkin's lymphoma), brain cancer, or central nervous system (CNS) cancer. As indicated in Table 1, the cancer types were determined by the International Classification of Diseases code (ICD-0-02) and the International Agency for Research on Cancer, International Classification of Childhood Cancers histology codes (IARC, 2003).
A comprehensive list of NPL sites was located on the U.S. EPA Web site (http://www.epa.gov/superfund/sites/query/basic.htm). …