West Nile cases surge to earliest, worst start in over two decades

West Nile virus has gotten off to its earliest and worst start in more than two decades, with the Centers for Disease Control and Prevention confirming at least 48 U.S. cases and 38 severe neuroinvasive illnesses by June 30. That pace is far ahead of normal for the end of June, when the average since 2004 has been about 10 cases, and CDC data show 23 states have already reported West Nile activity.

Arizona is carrying much of the burden. Maricopa County, which includes Phoenix, accounted for 29 of Arizona’s 32 cases and four deaths so far this year, and county health officials confirmed the first West Nile death of the 2026 season on June 16. That death involved an older adult with underlying health conditions.

West Nile is the leading cause of mosquito-borne disease in the contiguous United States. Most infected people never develop symptoms, but about one in five get fever or other illness, and fewer than 1% develop severe neurologic disease such as meningitis or encephalitis. The risk of neuroinvasive disease is higher in older adults and in people with immunocompromising conditions, and CDC surveillance shows hospitalization rates for these cases are high.

The virus has been part of the U.S. public-health landscape since it was first recognized in New York in 1999, and it peaked in 2003, when nearly 10,000 cases were reported. The CDC updates its seasonal data every one to two weeks from June through December, and the figures are preliminary. The CDC's historic dashboard tracks U.S. West Nile data from 1999 through 2025.

With Independence Day travel and outdoor gatherings approaching, the CDC and Maricopa County health officials urged people to cut mosquito exposure now: use EPA-registered insect repellent, including products with DEET; wear long, loose-fitting clothing; avoid outdoor exposure at dusk and dawn when mosquitoes are most active; keep mosquitoes out with screens or air conditioning; and dump standing water wherever it collects, even in something as small as an overturned bottle cap.