Current West Nile Virus Information for San Mateo County

2024

A total of 27 dead birds have tested positive for West Nile virus in 2024.

Most recently, in mid-September, 4 dead birds collected from Menlo Park (1 bird), Portola Valley (1 bird), San Carlos (1 bird), and North Fair Oaks (1 bird; unincorporated San Mateo County) tested positive for West Nile virus.

Additional birds collected earlier in the year from Atherton (4 birds), Foster City (2 birds), Menlo Oaks (2 birds; unincorporated San Mateo County), Menlo Park (10 birds), North Fair Oaks (1 bird; unincorporated San Mateo County), Redwood City (1 bird), San Carlos (1 bird), San Mateo (1 bird), and West Menlo Park (1 bird; unincorporated San Mateo County) had also tested positive for West Nile virus.

As of September 16, 2024, a total of 419 dead birds have been reported, of which 129 were in testable condition.

As of September 16, 2024, the District has tested over 4,500 mosquitoes. So far in 2024, no mosquito pools have tested positive for West Nile virus in San Mateo County.

This map includes approximate locations of West Nile virus positive samples in 2024. The map is lagged a little, so some of the most recent birds are not yet included on the map.

In late April, we started our sentinel chickens for the upcoming season.

Learn more about West Nile virus activity throughout California.

2023

In 2023, no mosquito pools tested positive for West Nile virus in San Mateo County. No sentinel chickens tested positive for West Nile virus. For information about West Nile virus in humans and horses, visit: https://westnile.ca.gov/ or www.cdfa.ca.gov/AHFSS/Animal_Health/Wnv_Info.html

In 2023, a total of 15 dead birds tested positive for West Nile virus in San Mateo County. Positive birds were found in Belmont (1), Burlingame (1), Foster City (1), Redwood City (1 in Redwood City; 3 in Redwood Shores area; 2 on the border of Redwood City and North Fair Oaks), San Carlos (1), and Menlo Park (5). Additional mosquito trapping and testing done in areas where dead birds were found did not found any positive mosquitoes.

Learn how to avoid mosquito bites and select a safe, effective mosquito repellent.

Page last reviewed: September 16, 2024

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