JMIR Publications

ABSTRACT

Background:

Historically, NRSS classifies U.S. counties as free from terrestrial rabies if, over the previous 5 years, they and any adjacent counties did not report any rabies cases, and they tested ≥15 reservoir animals or 30 domestic animals. Data from state and territorial public health departments and USDA Wildlife Services were analyzed to evaluate this definition.

Objective:

To assess the National Rabies Surveillance System (NRSS) criteria for designating U.S. counties as free from terrestrial rabies and provide more precise county-level freedom assessments.

Methods:

A zero-inflated negative binomial model created county-level predictions of the probability of rabies freedom and expected number of rabies cases reported. Data used included all animals submitted for laboratory diagnosis of rabies in the United States during 1995-2020 in skunk and raccoon reservoir territory, excluding bats and bat variants.

Results:

We analyzed data from 14,642 county-years in raccoon reservoir territory and 30,120 county-years in skunk reservoir territory. Only 9/1065 raccoon county-years and 27/3411 skunk county-years that met the historical rabies-free criteria reported a case the following year (99.2% negative predictive value for each), of which two were attributed to unreported bat variants. County-level model predictions displayed excellent discrimination for detecting zero cases (AUCs 0.89-0.97) and good estimates of cases reported (correlations 0.77-0.82 in raccoon territory, 0.44-0.52 in skunk territory) the following year. Counties classified as rabies free rarely (0.8%) detect cases the following year.

Conclusions:

Model-based analyses can provide more nuanced county-level risk estimates. However, all counties should stay alert to rabies caused by bat variant spillovers and animal translocations.