Signalment Changes in Canine Leptospirosis between 1970 and 2009

BACKGROUND Previous studies have identified large breed, male, outdoor dogs of herding or working groups to be at increased risk for Leptospira infection. Exposure risk factors may change over time, altering the signalment of dogs most commonly diagnosed with leptospirosis. OBJECTIVES The objectives of this study were to evaluate possible signalment changes by decade in canine leptospirosis cases diagnosed at university veterinary hospitals in the United States and Canada using reports to the Veterinary Medical DataBase (VMDB) over a 40-year period (1970-2009). ANIMALS One thousand and ninety-one dogs with leptospirosis diagnosed among 1,659,146 hospital visits. METHODS Hospital prevalence of leptospirosis by decade was determined by age, sex, weight, and breed groups. Multivariable logistic regression models were created to evaluate the association between variables and the odds of disease for each decade. RESULTS Veterinary Medical DataBase hospital prevalence of leptospirosis in dogs, after a marked decrease in the 1970s and low rates in the 1980s, began increasing in the 1990s. Hospital prevalence significantly increased in dogs between 2 and 9.9 years of age (P < .05) and in male dogs (P < .05) in each decade since the 1980s. Among weight groups in the most recent decade (2000-2009), dogs weighing <15 pounds had the greatest odds of being diagnosed with leptospirosis (P = .003). CONCLUSIONS AND CLINICAL IMPORTANCE Hospital prevalence rates by age, weight, sex, and breed groups differed by decade. These changes may reflect changes in exposure risk, Leptospira vaccination practices for dogs, or both.