OCR Text |
Show North Davis County The total cancer burden of North Davis County, shown by the RR for all reportable cancers combined, is not elevated. There again was a slight increase in the RR for brain cancer, 2.10 (95% CI 1.07, 4.14) in 1999, but the RR returned to 0.95 (95% CI 0.44, 2.04) in 2000. South Davis County As in North Davis County the total cancer burden in South Davis County, shown by the RR for all re-portable cancers combined, is not elevated. In South Davis the highest cancer RR for the years 1990-1999 was for ovarian cancer in the year 1998 at a rate of 2.18 (95% CI 1.26, 3.77), but was not sustained in 1999. Brain cancer did not show the same elevated increase as in North Davis over the years 1997-1999 but the RR did show a similar decrease in 2000, to 0.39 (95% CI 0.10, 1.58). Layton City Due to the smaller population and the resulting likelihood of small number problems, only the rates for brain cancer, non-Hodgkhvs lymphoma, and soft tissue sarcoma were calculated. There are no significant trends or elevations for neither non-Hodgkin's lymphoma nor soft tissue sarcoma for the years 1990-1999. Brain cancer was slightly elevated in the years of 1997-1999 but in 2000 it returned to a baseline rate. The RRs in 1997-1999 were 2.06 (95% CI 1.08, 3.92), 1.87 (95% CI 0.98, 3.56), and 2.08 (95% CI 1.12, 3.86) respectively, but in 2000 the RR dropped down to 1.06 (95% CI 0.46, 2.41). The increase over the three years was not enough to be considered a statistically significant trend (Balesracci, 1996). Due to the heightened concern over a possible increase of brain cancer, not just in Layton, but also specifically in the area adjacent to the WES plant, an exposure assessment was conducted to see if there was a clustering of brain cancer cases in the highest areas of exposures from the plant. The State Public Health Department - Division of Epidemiology obtained the locations of the cases within a five-mile radius of the WES plant and plotted them on a map. The exposure of interest was from the WES stack emissions, which are distributed by the winds. The meteorological data obtained from HAFB were put into a frequency distribution graph (figure 13) to see if there were directions in which the wind blew most often. The wind blew most often in a westward direction from 100°, over the HAFB's runway. There were secondary and tertiary wind plumes directed south-southeast, from 310-330°, and north-northwest, from 160°, respectively. The wind frequencies were placed on a map of the five-mile area surrounding WES and the cases were then superimposed over the wind map. There was no obvious clustering of brain cancer cases in the years 1990- 1999 in the five mile radius around WES that were correlated with the wind plumes. Discussion The cancer burden within Davis County has been examined in depth and is now better understood by health professionals. Since cancer rates in Davis County are generally at or below state rates, there is little reason for alarm. Cancer is considered a rare disease. Therefore, in order for meaningful associations to be well understood concerning cancer rates, it is important to realize the importance of the study population. If the study population is too small and specific, the numbers of cases are too small and unstable to give any meaning. There are 36 tracts in Davis County as defined by the 1990 Census. Dividing the county into northern and southern halves gave large enough populations to produce a fair amount of confidence in the stability of the cancer rates (figure 14). As a result of the initial allegations linking brain cancer to dioxin stack emissions from WES, we narrowed our analyses of dioxin specific cancers to in order to further identify any possible cancer cluster. In interpreting these data the instability of these numbers must be taken into consideration. Despite the lack of evidence in the scientific literature linking dioxin to brain cancer, the three-year period 1997-1999 showed a mild elevation in the rates of brain cancer in Davis County. After the 2000 cancer registry data regarding brain cancer became available, the concerns of elevated brain cancer cases were eased with the dramatic decrease in cases throughout the county, as well as in North Davis and Layton specifically. While there was an increase in the incidence of brain cancer in Davis County in the years 1997-1999, this increase is not considered to be a statistically significant increasing trend. In order for a trend to be statistically significant there must be seven points in the same direction (Balesracci, 1996). Since there were no significant trends in cancer rates in Davis County, we attribute the three years of increased cancer rates to random variation. Utah's Health: An Annual Review Volume VIII 45 |