July 2018 West Nile Virus Update

San Mateo County

As of August 1, 2018, there have been 247 dead birds reported in San Mateo County. Of those, 66 have been suitable for testing and two have tested positive (3%) for West Nile virus (WNV). No mosquito pools or sentinel chickens have tested positive for West Nile Virus in San Mateo County in 2018.

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


WNV has been detected in 27 counties in 2018 (see map) compared to a five-year average of 33 counties at this date. Statewide, 4,632 birds have been reported and 1,110 have been tested with 181 positive results (16%). 480 mosquito pools have tested positive for WNV this year. In the San Francisco Bay Area, mosquito control districts in Alameda County and Santa Clara County fogged for adult mosquitoes in June, following WNV positive mosquito detections. Throughout California, there have been twelve (12) symptomatic human cases of WNV, compared to a five-year average of eight (8) at this date. Eleven (11) positive sentinel chickens have been reported in 2018 in California.