West Nile Virus Update – Ocotober 2019

San Mateo County

As of November 1, 2019, there have been 215 dead birds reported in San Mateo County. Of those, 53 have been suitable for testing and all 53 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


In 2019, as of November 1, West Nile virus has been detected in 33 counties in California (see map).  To date, 178 human cases of WNV have been reported from 20 counties, with the median age being 59 years old. No human cases have been reported from San Mateo County.

Throughout the state, 5,200 birds have been reported and 1,693 have been tested with 210 positive results (12%). Positive mosquitoes have been collected from 25 counties in California, for a total of 3,269 positive samples. Contra Costa County has recorded the only positive mosquito samples from the Bay Area coastal region.

Fifteen (15) horses and 135 sentinel chickens have also tested positive for WNV in California.