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Show statement is based on an overall increase in cancer, not any specific subtype, in human populations based on epidemiological and scientific studies. Due to the unknown relationship between dioxin and brain cancer in humans, the Davis County Health Department began a preliminary investigation into the allegations. The Utah Cancer Registry was contacted to verify the count of brain cancer cases given by the citizens in five zip codes: 84405, 84056, 84041, 84040, and 84015. Observed to expected (0/ E) ratios were obtained from the Utah Cancer Registry for brain cancer in each of the five zip codes, and there appeared to be an elevation of observed to expected brain cancer cases in zip code 84405. O/E ratios are the amount of disease observed in the case population compared to how much disease you expect to see for that case population. The amount of disease expected in the population is obtained by observing how much disease routinely arises in a population of that size, observed over a period of time. There appeared to be a nine-fold increase over the ten-year O/E ratio for zip code 84405. The local media was informed of the preliminary numbers and began publishing reports of a brain cancer epidemic in the areas around WES. Due to the preliminary data, an investigation was initiated into the cancer burden in the areas adjacent to WES, and in Davis County as a whole. Methods The number of cases for each year from 1990 to 1999 (1990-2000 for brain cancer) was obtained from the Utah Cancer Registry for each reportable cancer. The Utah Cancer Registry collects very extensive data on the number, location, and type of each reportable cancer in the state of Utah. The observed cases were stratified by 1990 census tract demarcations and the following age categories by year: 0-17, 18-24, 25-44, 45-64, and 65+. Initially, crude Rate Ratios (RRs) were calculated for the eight most common reportable cancers in Utah (bladder, breast, colon, lung, melanoma, ovarian, prostate, and uterine), as well as brain cancer, soft tissue sarcoma, non-Hodgkin's lymphoma, and all reportable cancers combined. Rate ratios are the rate of a disease (based on the number of cases and the population) in a case group compared to the rate in a control group (again based on the number of cases and the population). In this study, the case populations are in Davis County, Utah. The control group is comprised of the entire state of Utah. Age adjusted RRs were used to measure the cancer burden from 1990 to 1999 (1990-2000 for brain cancer) in the areas adjacent to WES and throughout Davis County. These were calculated by first calculating crude cancer rates per 100,000 people per year and then age adjusting them by the direct method (Pagano, M. and Gauvreau, K., 2000) to the Utah population. These rates and the state rates were then used to calculate age adjusted RRs (see Figures 1-12). In age adjusting the cancer RRs, Utah's state population was used because we could easily obtain the observed number of cases of cancer from the state cancer registry and also because Utah generally has lower cancer rates than most of the United States (SEER Cancer Statistics Review, 1973-1998), making Utah a more appropriate comparison. Due to the reported nine-fold increase in brain cancer in zip code 84405, further investigation was conducted into both the number of brain cancer cases and the population of that zip code. The population had been underestimated by almost ten-fold. It was then determined that zip code population estimates were unreliable, and the U.S. Census Tract population was therefore used to recalculate the denominator needed to calculate the RRs. The census tract boundaries have changed from the 1990 Census to the 2000 Census; it was necessary to standardize the 2000 census tract boundaries to the 1990 census tracts. This was done by utilizing a census bureau chart which indicated the changes between the 1990 and 2000 census tracts and blocks (U.S. Census Bureau, 2000). Once the population data by tract were determined for the two censal years of 1990 and 2000 it was necessary to interpolate the population numbers for the years 1991-1999; this was done by assuming steady growth in the years between 1990 and 2000. The age adjusted RRs for the eight most common reportable cancers and all reportable cancers combined were analyzed for each of the following locations as delineators: North Davis County, South Davis County, and Davis County as a whole (Figure 14). Brain cancer, soft tissue sarcoma, and non-Hodgkin* s lymphoma were analyzed by the same locations, but also further stratified within Layton. The census tracts used to demarcate Layton were 1251.01, 1251.02, 1254.02, 1257, 1258.01, 1258.02, 1258.04, 1259.03, 1259.04, and 1260. These were chosen because the initial complaint of a brain cancer cluster, due to exposure to dioxin, was cited in this general area. The border designating North and South Davis County is a cultural demarcation made Utah's Health: An Annual Review Volume VIII 41 |
