Year of Publication

2016

College

Public Health

Degree Name

Dr. of Public Health (Dr.P.H.)

Committee Chair

David Mannino, MD

Committee Member

Ramona Stone, PhD, MPH

Committee Member

W. Jay Christian, PhD, MPH

Abstract

Non-Hodgkin’s Lymphoma (NHL) is a category of cancers that arise from the lymphocytes of the immune system. The rates of NHL in the United States and Kentucky began to rise in the mid-20th Century, shortly after the manufacture, use, and disposal of numerous chemical substances began to increase during and after the Second World War. While the etiology of NHL is not fully known, there are several chemical substances for which evidence exists of a possible link between exposures and development of NHL and other cancers. Several of these substances are also present in sites within Kentucky designated by the US Environmental Protection Agency as hazardous waste sites under the Superfund program. The present investigation sought to determine whether residential proximity to Superfund sites in Kentucky was a significant risk factor for NHL. Geospatial coordinates for all Superfund sites in Kentucky were obtained, along with US Census 2010 population data at the census tract level, and de-identified data from the Kentucky Cancer Registry for all NHL cases between 1995 and 2012, including residential geospatial coordinates. Incidence data was calculated at the level of census tract, except for <5km buffer rings and 5-10km buffer circles around each Superfund site, whose NHL incidence data was calculated separately. Residence within the <5km and 5-10km buffer zones were the exposure variables, and other potentially relevant covariates were considered for the models, and tested for multicollinearity and significance.

Because of spatial autocorrelation of NHL incidence data and nonstationarity uncovered during exploratory regression and diagnostics, geographically weighted regression was used in addition to ordinary least squares regression. Using the best-fitting models, it was determined that residence less than 5km and between 5-10km from the nearest Superfund site were both significant factors in elevated cumulative NHL incidence rates. The Beale Code for rural/urban characteristics of the census tract was another significant predictor, with more rural areas having higher NHL incidence rates. Directions for future research, public health implications, and potential strategies for distal and proximal interventions are presented based on the results of this study.

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