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West Nile Virus Update – December 2019

San Mateo County

In the 2019 calendar year, the District closed out one of its lowest seasons for West Nile virus activity since the virus first appeared in San Mateo County in 2004.  No virus was detected in the county this year in any of the standard WNV surveillance indicators.

Surveillance Factor

Previous 10-year average (2009-2018)

2019

Dead birds reported

378

233

WNV+ Birds / Birds tested

9.6 / 84.3

0/61

% WNV+ Birds

11.4%

0%

WNV+ Mosquito samples

2.7

0

WNV+ Sentinel chickens

0

0

WNV+ Horses

0

0

WNV+ Human cases

0

0

The District continues to ask 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 westnile.ca.gov.

California 

In 2019, as of December 20, West Nile virus had been detected in 34 counties in California (see map).  To date, 214 human cases of WNV have been reported from 25 counties.  Six WNV-related fatalities were reported from California in 2019, including one from Santa Clara County. No human cases have been reported from San Mateo County.

Throughout the state, 1,893 dead birds were tested with 226 positive results (12%). Positive mosquitoes were collected from 25 counties in California, for a total of 3,288 positive samples.  At this time in 2018, 1,963 WNV positive mosquito pools had been reported from 29 counties.

Fifteen (15) horses and 139 sentinel chickens have also tested positive for WNV in California.

Commands