Factors Associated with Rabid Animals Since the Introduction of Raccoon Rabies Variant in Massachusetts, 1992–2007

Abstract

Rabies virus has been identified in 26 animal species since the introduction of the raccoon rabies variant (RRV) into the Commonwealth of Massachusetts in 1992. This study used data from 47,162 testable specimens, including 4538 (9.62%) rabid animals, to produce a multi-categorical logistic regression model to identify factors associated with a positive rabies laboratory test. The model was adjusted by the animal type and animal species, using the least tested and the least found rabid animal species pooled as a reference group. The c-statistic for the final model was 0.94, and a receiver operator characteristic curve plot shows the increased sensitivity and the decreased false-positive proportion of the model. Introduction of RRV into the county where the animal was found (OR = 17.3), not up-to-date on vaccination (OR = 3.88), exposure of multiple humans, or pets, or human and pet (OR = 1.88), reason for rabies testing (using human exposure only as the reference group, the odds ratio for both human and animal exposure is 2.14; for pet/companion exposure only is 2.96; and for undefined reasons/sick animal is 1.49), reported syndromes/observation of aggression (OR = 4.13), ataxia (OR = 1.36), disorientation (OR = 1.67), paralysis ( OR = 1.37), and the presence of unexplained wounds (OR = 1.27) were all significantly associated with a positive rabies testing result at the alpha = 0.05 level.