West Nile virus (WNV) Activity
Year-to-Date Statistics for 2026
2026 WNV+ Mosquito Samples
A sample is a collection of mosquitoes from a mosquito monitoring trap. Positive mosquito samples from routine and randomized trapping provide insight into the spread of West Nile virus.
So far in 2026, 3 mosquito samples have tested positive for West Nile virus in Alameda County.
| City/Community | Date of Confirmed Detection | # of WNV+ Mosquito Samples |
|---|---|---|
| Newark | 6/15/2026 | 1 |
| 6/16/2026 | 1 | |
| Union City | 6/16/2026 | 1 |
| Total # of WNV Positive Mosquito Samples this year | 3 |
2026 WNV+ Dead Birds
Residents report dead birds through the California Department of Public Health (CDPH) Dead Bird Surveillance program. After a bird is reported, the District collects it and tests it for West Nile virus if it meets the established testing criteria. Positive dead birds also provide insight to West Nile virus activity.
So far in 2026, a total of 18 birds in Newark, Fremont, and Livermore have tested positive for West Nile virus in Alameda County.
| City/Community | Date of Confirmed Detection | # of WNV+ Birds |
|---|---|---|
| Newark | 5/1/2026 | 1 |
| 5/29/2026 | 1 | |
| 6/9/2026 | 2 | |
| 6/10/2026 | 1 | |
| 6/22/2026 | 2 | |
| 6/26/2026 | 1 | |
| 6/29/2026 | 1 | |
| 6/30/2026 | 2 | |
| 7/1/2026 | 4 | |
| Fremont | 6/24/2026 | 1 |
| 7/1/2026 | 1 | |
| Livermore | 7/1/2026 | 1 |
| Total # of WNV Positive Birds this year | 18 |
West Nile Virus Activity (WNV+) in Alameda County
Visit the full VectorSurv site to learn more about mosquito and disease activity throughout California.
What does the Alameda County Mosquito Abatement District do after a dead bird and/or a mosquito sample tests positive for West Nile virus?
When a dead bird or mosquito sample tests positive for West Nile virus (WNV) in Alameda County, District staff respond by:
- Deploying additional mosquito monitoring traps in the area to collect mosquitoes and further assess potential WNV activity.
- Inspecting and treating standing water sources by locating standing water sources, such as storm drains, ponds, and neglected swimming pools, and eliminating them or applying larvicides when appropriate.
- Expanding public outreach by working with community partners and local city and county agencies to share information about West Nile virus and mosquito prevention.
- Implementing targeted mosquito control treatments as needed.
West Nile Virus Activity in Alameda County: Past 10-Year Overview
| 2017 | 2018 | 2019 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 | 2026 | |
|---|---|---|---|---|---|---|---|---|---|---|
| Birds | 2 | 20 | 0 | 8 | 3 | 0 | 82 | 53 | 6 | 18 |
| Mosquitoes | 0 | 15 | 0 | 0 | 0 | 0 | 22 | 19 | 0 | 3 |
| Humans | 1 | 0 | 0 | 0 | 0 | 1 | 2 | 0 | 0 | 0 |
Learn more about West Nile virus Activity in California and the United States
To take a look at West Nile virus activity throughout California, visit the California Department of Public Health (CDPH) West Nile virus website (westnile.gov).
To take a look at West Nile virus activity throughout the United States, visit the U.S. Centers for Diseases Control and Prevention (CDC) West Nile virus website (cdc.gov/west-nile-virus/).
Past West Nile virus Activity in Alameda County