Evaluation of temporal and spatial clustering of horses with Corynebacterium pseudotuberculosis infection.
OBJECTIVE
To determine whether horses with Corynebacterium pseudotuberculosis infections that were examined at a veterinary medical teaching hospital between July 1, 1992, and June 30, 1994 had patterns of temporal or spatial clustering.


METHODS
134 case and 800 control horses randomly selected from all non-case horses admitted during the study period.


METHODS
Admission date and geographic location were determined. Scan, Cuzick & Edwards', and Knox tests were applied to determine whether case horses had patterns of temporal or spatial clustering.


RESULTS
For all windows > or = 3 days (134 case horses) and > or = 7 days (subset of 69 case horses), results of the Scan test were significant. Results of Cuzick & Edwards' test were significant for all data sets. A significant spatial cluster of case horses was observed for October, November, and December 1992. Results of the Knox test were significant for temporal intervals between 7 and 56 days and spatial intervals between 4.3 and 6.5 km. Higher Knox(x) proportions were observed for temporal intervals of 0 to 7, 8 to 14, 22 to 28, and 29 to 35 days.


CONCLUSIONS
Significant spatial and temporal clustering of horses with C pseudotuberculosis infection was detected.


CONCLUSIONS
Analysis of the results strongly indicates that this disease is directly or indirectly (ie, short distance and time) transmitted. In addition, data analyses indicated an incubation period of 3 to 4 weeks. The disease could be transmitted through horse-to-horse contact or from infected to susceptible horses via insects, other vectors, or contaminated soil.
Doherr
M G
MG
School of Veterinary Medicine, Department of Medicine and Epidemiology, University of California, Davis 95616-8737, USA.
Carpenter
T E
TE
Wilson
W D
WD
Gardner
I A
IA
D000818:Animals; D002140:California / Q000453:epidemiology; D003354:Corynebacterium Infections / Q000453:epidemiology / Q000635:transmission / Q000662:veterinary*; D016925:Corynebacterium pseudotuberculosis; D006734:Horse Diseases / Q000453:epidemiology / Q000382:microbiology / Q000635:transmission*; D006736:Horses; D013029:Space-Time Clustering