Spatial and temporal distribution of selected canine cancers in Michigan, USA, 1964-1994

Although rates are commonly used to compare regional disease occurrence, ra te-independent methods might also be useful in circumstances where geograph ic occurrence of a disease is known, but calculation of disease rates is no t feasible. This is frequently the case for diseases in companion animals, where accurate enumeration of populations-at-risk is often arduous. This st udy had two objectives: to demonstrate a rate-independent method for invest igating disease aggregation in companion animals; and, to assess the spatia l and temporal clustering of canine cases of four cancers that are biologic ally similar in dogs and humans. Geographic information systems and point-p attern analysis were used to assess the spatial and temporal clustering of incident cases of four types of canine cancer in three counties in Michigan between 1964 and 1994, and to generate hypotheses concerning disease aggre gation. Significant (P less than or equal to 0.01) spatial clustering was f ound that varied by county and cancer type. No definitive temporal patterns could be deduced from a temporal analysis of the cases of canine cancer in this study. These results demonstrate distance-based methods for assessing clustering of disease, and suggest that processes determining the aggregat ion of canine cancer cases do not act in a spatially uniform manner. (C) 19 99 Elsevier Science B.V. All rights reserved.