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West Nile virus activity in San Gabriel Valley

Updates about West Nile virus in the San Gabriel Valley

Last Updated on 11/21/2023​ ​8 AM

Testing has officially concluded for the 2023 mosquito season. 

Our agency reports data related to mosquitoes. Human cases are reported by the L.A. County Department of Public Health and Pasadena Health Department.

The San Gabriel Valley Mosquito & Vector Control District has been tracking West Nile virus activity in mosquito populations since 2003. Dead bird data is stored with the California Department of Public Health. You can access the dead bird data HERE.

West Nile virus Facts

  1. West Nile virus is the most common mosquito-borne disease that affects residents in Los Angeles County
  2. Public health agencies detect West Nile virus every year in L.A. County. This means the virus is found naturally in our city environments, which means it's endemic.
  3. Our agency uses routine traps to collect samples of mosquitoes. The mosquito samples are tested for mosquito-borne diseases, such as West Nile virus. In addition, dead birds, which can carry West Nile virus, are submitted for testing.

Year-to-Date Statistics for 2023

2023 WNV+ Mosquito Samples

A sample is a random collection of 10-50 mosquitoes from a trap. Positive mosquito samples from routine and randomized trapping provide insight into the spread of West Nile virus.

City/CommunityDate of First DetectionPositives
Alhambra06/21/233
Altadena08/17/231
 Arcadia09/13/23 1
Azusa 07/06/23 6
Baldwin Park08/02/233
Bradbury 08/01/234
Charter Oak06/22/236
Claremont08/01/2314
Covina06/08/2359
Duarte  08/15/231
East San Gabriel08/01/23
Glendora06/22/2322
 Irwindale08/08/23 5
La Puente08/30/23 7
La Verne08/01/2315
Monrovia 10/26/23 
Monterey Park09/06/235
Pasadena07/25/235
Pomona07/25/2316
Rosemead 08/15/235
San Dimas 08/01/2310
San Gabriel  09/12/23 5
Sierra Madre 07/11/233
South Monrovia Island09/26/23 
South Pasadena07/25/231
Temple City07/18/232
 Vincent06/20/233
Walnut07/25/2312
West Covina07/20/2328
 Total # of Positive Mosquito Samples this Year245

 2023 WNV+ Dead Birds

People report dead birds they observe in their community. Positive dead birds are an indication West Nile virus is widespread in the region.

City/CommunityDate of First DetectionPositives
Covina 06/02/2310
 Glendora08/31/231
La Verne09/26/231
Pomona 09/21/231
San Dimas08/31/231
Temple City  08/15/231
Total # of Positive Dead Birds This Year15

Take a look at mosquito disease activity throughout California using the VectorSurv Map!

To experience the entire site, visit: VectorSurv.org