2012 Second Worst Year for West Nile Virus

4,531 cases, 183 deaths

West Nile virus cases in the U.S. hit 4,531 as of Tuesday, including 183 deaths, making 2012 the second-worst year ever for the mosquito-borne illness, the Centers for Disease Control and Prevention reported Wednesday.

Cases were up 8% from last week, to 282, including 15 more deaths reported, said Erin Staples, a West Nile expert for the CDC. The numbers don't represent a new wave of mosquito activity, but rather cases slowly working their way through to the CDC, she said. "It's a reporting lag. We're not hearing from our state partners that they're getting a deluge of cases."