Skip to main content

West Nile Virus Activity 2023

May contain: animal, bird, and crow

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.

2023 West Nile Virus Activity

West Nile Virus Positive 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
 Arcadia09/13/23 1
Azusa 07/06/23 6
Baldwin Park08/02/233
Bradbury 08/01/234
Charter Oak06/22/236
Duarte  08/15/231
East San Gabriel08/01/23
 Irwindale08/08/23 5
La Puente08/30/23 7
La Verne08/01/2315
Monrovia 10/26/23 
Monterey Park09/06/235
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
West Covina07/20/2328
 Total # of Positive Mosquito Samples this Year245

West Nile Positive Dead Birds 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
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: