West Nile Virus Surveillance Update for April 27, 2018

San Mateo County

As of April 27, 2018, there have been 46 dead birds reported in San Mateo County. Of those, 13 have been suitable for testing and two have tested positive (15%) for West Nile virus (WNV). San Mateo and Santa Clara counties are the only counties with positive WNV dead birds (4) thus far this year. 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 three counties in 2018 (see map), compared to a five year average of five counties at this date. Statewide, 851 birds have been reported and 149 have been tested with four positive results (3%). This percentage is the same as it was in 2017 at this date. One mosquito pool tested positive for West Nile virus from San Bernardino County. No positive sentinel chickens or human cases have yet been reported in California.