historically, most cases of encephalitis reported to the cdc occurred in the north of the mainland united states. jcv disease most likely has a broader distribution, but is unidentified and under-reported, because testing is not considered and not straightforward. in 2013, of 10 states reporting cases, eight states reported their first jcv cases: georgia, idaho, massachusetts, minnesota, new hampshire, oregon, pennsylvania, and rhode island.