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West Nile Virus Activity 2021

May contain: animal, bird, and crow

West Nile virus Facts

  1. West Nile virus is the most common mosquito-borne disease that affect 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 colect samples of mosquitoes. The mosquito samples are tested for a mosquito-borne diseases, such as West Nile virus. In addition, dead birds, which can carry West Nile virus, are submitted for testing.

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


2021 West Nile Virus Activity

 Last update: July 22, 2021

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 of the spread of West Nile virus.

City/CommunityNumber of WNV+ Mosquito SamplesDate of first report
Baldwin Park17/22
San Dimas57/19
South Pasadena27/19
Unincorporated LA County (Vincent neighborhood)46/21
Unincorporated LA County (West Puente Valley neighborhood)17/12
West Covina116/21
TOTAL 47--


West Nile Virus Positive 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/CommunityNumber of WNV+ dead birdsDate of first report
 South Pasadena16/7
West Covina37/19