West Nile Virus Update – August 2019

San Mateo County

As of September 3, 2019, there have been 179 dead birds reported in San Mateo County. Of those, 38 have been suitable for testing and all 38 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 2019.

The District asks residents to report dead birds. Specimens that appear to have been dead for less than 24 hours and are in good condition will be tested for WNV.  Residents should contact the state WNV hotline at 877-WNV-BIRD (968-2473). Reports can also be made online at


West Nile Virus activity within California increased considerably during the month of August. WNV has been detected in 26 counties in 2019 (see map), compared to a five year average of 37 counties at this date. There have been 57 human cases of WNV reported in California this year, with 27 of the human cases from Fresno County. Two of the cases were fatalities. Statewide, 4,090 birds have been reported and 1,231 have been tested with 91 positive results (7%).  Positive mosquito samples have been detected in 24 counties throughout California, with a total of 2,516 positive samples. None of the positive mosquito samples have been from the Bay Area coastal region. Six horses and 53 sentinel chickens have also tested positive for WNV in California.