Spatial and temporal patterns of Leptospira infection in dogs from northern California: 67 cases (2001-2010)

Objective-To conduct an epidemiological analysis of the spatial and temporal distribution of canine leptospirosis cases in northern California and detect spatial clustering in any region. Design-Retrospective case-control study. Animals-67 dogs with leptospirosis and 271 control dogs. Procedures-Medical records of case and control dogs were reviewed. Spatial coordinates of home addresses of the study population were analyzed visually and statistically via a Cuzick-Edwards test and spatial, temporal, and space-time permutation scan statistics. Results-Cases were distributed around the San Francisco Bay region as well as in the Sierra Nevada foothills near Sacramento, Calif, whereas controls were principally distributed along route I-80 between San Francisco and Sacramento, Calif. Clustering was found for the second through sixth nearest neighboring cases via the global spatial cluster test. A local spatial cluster of 30 cases was identified in San Francisco (95% confidence interval, 1.3 to 7.0), and a temporal cluster of 18 cases was identified from May 2003 through May 2004 (95% confidence interval, 1.4 to 6.5). No significant space-time cluster was identified. Conclusions and Clinical Relevance-The use of geographic information systems provided a visual representation of the results of statistical analysis for the location and time at which leptospirosis cases occurred. This useful tool can be used to educate veterinary practitioners and the public about a potentially fatal zoonotic disease and direct vaccination strategies to help prevent disease occurrence.