West Nile Virus Update – September 2019

San Mateo County

As of October 2, 2019, there have been 191 dead birds reported in San Mateo County. Of those, 44 have been suitable for testing and all 44 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 report birds online to the state WNV hotline at Live operators will also be available to take dead bird reports over the phone at 877-WNV-BIRD (968-2473) only through October 11, 2019.


West Nile virus has been detected in 33 counties in California so far in 2019 (see map).  To date, 112 human cases of WNV have been reported; 44 of these have come from Fresno County. No human cases have been reported from San Mateo County.

Throughout the state, 4,656 birds have been reported and 1,481 have been tested with 175 positive results (12%). Positive mosquitoes have been collected from 24 counties in California, for a total of 3,125 positive samples. None of the positive mosquito samples have been from the Bay Area coastal region.

Thirteen (13) horses and 114 sentinel chickens have also tested positive for WNV in California.