During the 1999 encephalitis outbreak, there were 62 human cases and seven deaths. In 2000, there were 21 diagnosed cases and two deaths. However many infected people showed mild flu-like symptoms or no symptoms at all. In 2000, West Nile virus had been found in New York, New Jersey, Connecticut, Rhode Island, Massachusetts, Vermont, Virginia, Maryland, Pennsylvania, North Carolina, and New Hampshire. Positive horses have been found in New York, New Jersey, Connecticut, Rhode Island, Pennsylvania, and Massachusetts.
Dead birds can be an indication that West Nile virus is present in an area.