CONCORD, CALIFORNIA - The Contra Costa Mosquito & Vector Control District (District) has confirmed three more groups of mosquitoes have tested positive for West Nile virus (WNV) in Contra Costa County. Two groups of mosquitoes were trapped in Brentwood and one group was collected in Discovery Bay. The positive mosquitoes from Brentwood were collected during District surveillance following last week's Adult Mosquito Control efforts in Brentwood. Preliminary results suggest the treatment appears to have been effective, but the risk of WNV remains.

So far this year, a total of 11 groups of mosquitoes have tested positive for WNV in Contra Costa County. In past years, the District has confirmed WNV in mosquitoes well into October, so it's important for county residents to remember, Labor Day is not the unofficial end of WNV season.

"As Contra Costa County traditionally stays warm into October, we could continue to see WNV for several more weeks. So, it's not time to put your guard down when it comes to mosquitoes. Use precautions to reduce the risk of mosquito bites and report dead birds because those reports can help direct our surveillance and control efforts,"said the District's Scientific Program Director Steve Schutz, Ph.D.

Contra Costa County residents can reduce the risk of mosquito bites and WNV by:

  • Dumping or draining standing water. Mosquitoes develop from egg to adult in water.
  • Defending yourself - use repellents containing DEET, Picaridin, or Oil of Lemon Eucalyptus
  • Keeping swimming pools chlorinated and filtered because just one neglected pool can produce up to 1 million mosquitoes and affect people several miles away
  • Avoiding the outdoors when mosquitoes are present, typically dawn and dusk
  • Reporting dead birds to the state hotline by phone at (877) WNV-BIRD (968-2473) or online

Since 2005, 70 people in Contra Costa County have been diagnosed with West Nile virus. In 2006, two people died from the disease. For current human case information, please contact Contra Costa Health Services at 888-959-9911.
Contra Costa Mosquito & Vector Control District, an independent special district and public health agency, is located at 155 Mason Circle in Concord. Contact the District to report mosquito problems online or at (925) 685-9301.