The Centers for Disease Control and Prevention says Arizona ranks third so far this year for human West Nile infections with 16 confirmed cases.

California leads the nation with 84 cases, while South Dakota is second with 28.

Arizona was the nation's epicenter for West Nile virus last year.

Sixteen people died and nearly 400 sought treatment for the virus. But because only a fraction of those infected seek medical care, health officials estimate the actual number of Arizonans infected last year was closer to 40,000.