CONTRA COSTA COUNTY, CALIFORNIA – West Nile virus is again circulating in Contra Costa County, with local officials confirming the first infected mosquitoes and bird of the year in the 925.
The Contra Costa Mosquito and Vector Control District recently found a West Nile-positive mosquito sample near Pacheco Marsh along the Martinez waterfront. Days later, officials confirmed that a young American crow from El Cerrito had also tested positive for the virus.
Together, the two findings show that West Nile virus is active in the local bird-and-mosquito cycle that can eventually put people at risk. The district’s 2026 surveillance map now lists the Martinez mosquito sample.
That does not mean every mosquito in Contra Costa County is infected, nor does it mean residents should avoid summer evenings outdoors. But it is an early-season reminder that the familiar backyard pest can carry a genuinely serious disease…