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Current West Nile Virus Information for San Mateo County

The District collects and tests dead birds reported by residents. Dead birds should be in good condition without signs of decay or trauma. All bird species are accepted except water fowl, poultry or pigeons.

To report a dead bird, residents should call the California state West Nile virus hotline at 1-877-WNV-BIRD (1-877- 968-2473). Online reports can be made at

San Mateo County

As of October 1, 2021, there have been 262 dead birds reported in San Mateo County. Of those, 69 have been suitable for testing and all have tested negative for West Nile virus (WNV). No mosquito pools or sentinel chickens have tested positive for West Nile virus in San Mateo County in 2021.


Map of California with county outlines. Counties are colored blue (indicates WNV activity without human cases), green (WNV activity with human cases), or white (no WNV activity). San Mateo County is white (no WNV activity as of 10/1/21).

Statewide, 4,556 dead birds have been reported and 1,498 have been tested with 201 positive results (13%). This is similar to bird data from last year, when 263 dead birds had tested positive at this date. This is low compared to a five-year average of 525 positive dead birds by the end of September. So far in 2021, 2,191 mosquito samples have tested positive for West Nile virus from 25 counties. Statewide, 92 sentinel chickens have tested positive from 13 counties.

There have been 62 human cases of West Nile virus with four fatalities. Most West Nile virus activity this year within California is in the central valley and southern California, although Alameda County detected their first West Nile virus positive bird at the end of September. 


Learn more at the California Department of Public Health's West Nile Virus website


Date last reviewed: October 13, 2021

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