West Nile Virus Surveillance

Overview

How to Interpret West Nile Virus Surveillance Data

The District’s West Nile virus surveillance program reports several types of positive West Nile virus results, including dead birds, mosquito samples (“pools”), sentinel chickens, and human cases.

For more information about the District’s West Nile virus and mosquito population surveillance, visit the Mosquito Surveillance page.

For real-time West Nile virus data for California, visit the California Vectorborne Disease Surveillance Maps (CalSurv) page.

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West Nile Virus Surveillance
July 7, 2017

San Mateo County

As of June 630, 2017, there have been 215 dead birds reported in San Mateo County. Of those, 45 have been suitable for testing and 1 has tested positive (2%) for West Nile Virus (WNV). No dead squirrels or mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year.

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West Nile Virus Surveillance Update
June 7, 2017

San Mateo County

As of June 6, 2017, there have been 134 dead birds reported in San Mateo County. Of those, 21 have been suitable for testing and 1 has tested positive (5%) for West Nile Virus (WNV). No dead squirrels or mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year.

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West Nile Virus Surveillance Update
April 28, 2017

San Mateo County

As of April 28, 2017, there have been 56 dead birds reported in San Mateo County. Of those, 15 have been suitable for testing and 1 has tested positive (7%) for West Nile Virus (WNV). No dead squirrels or mosquito pools have been tested for West Nile Virus in San Mateo County thus far this year.

Post Theresa Shelton

First Positive Bird of 2017 in San Mateo County

It is unusual to detect West Nile Virus in dead birds during the winter months.  West Nile Virus season begins mid-April, with most activity in the summer.  However, residents can report some species of dead birds (crows, ravens, scrub-jays, finches, sparrows, hawks and owls) year-round online at westnile.ca.gov and the District laboratory will test fresh specimens without signs of trauma (roadkill or partially decomposed specimens cannot be tested).The first West Nile Virus positive bird of 2017 in San Mateo County was detected in Redwood City.

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West Nile Virus Dead Bird Hotline

The West Nile Virus Dead Bird Hotline, operated by the California Department of Public Health (CDPH), will not be answered by live operators after October 14, 2016 until next spring.  However, residents can still call the phone number 1-877-WNV-BIRD and leave a message or fill out an online form at westnile.ca.gov to report dead birds.  During the winter season, the District will continue to collect and test suitable birds of the following groups:  corvids, finches, sparrows, owls, and hawks.

Risk Assessment provided by California Department of Public Health
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WNV Risk Assessment
San Mateo County

The California Department of Public Health generates a risk assessment level ranging from 1-5 for West Nile Virus (WNV).  The risk level is determined by analyzing a combination of data on mosquitoes and infection rates gathered by the District, weather patterns and the state WNV hotline.  The risk levels are explained as:                

Risk Rating 1.0—2.5 Normal Season, “No Alert Level”

Regular district operations

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Efficacy of ULV adulticide and mosquito reduction
San Mateo County, 2016

Material

Date

City

Efficacy

% Reduction

Press release

No West Nile Virus Found in Mosquitoes Collected from Atherton This Week
FOR IMMEDIATE RELEASE

Burlingame, CA – 10 August 2016

Mosquito samples collected from Atherton following San Mateo County Mosquito and Vector Control District’s adult mosquito control treatment on Thursday, Aug. 4th, have tested negative for West Nile virus.

“Although we didn’t find infected adult mosquitoes this week, residents are encouraged to continue to take basic precautions against mosquito bites,” said the District’s Public Health Education and Outreach Officer, Megan Caldwell.

Residents should:

Press release

From California Department of Public Health: CDPH Confirms First Human West Nile Virus Death of 2016
FOR IMMEDIATE RELEASE

Sacramento, CA – August 5th, 2016

California Department of Public Health (CDPH) Director and State Health Officer Dr. Karen Smith today announced the first confirmed death in California due to West Nile virus (WNV). The deceased person was a senior citizen in Sacramento County.

Press release

Dead Birds are First Indication of West Nile Virus in San Mateo County in 2016
FOR IMMEDIATE RELEASE:

Dead Birds are First Indication of West Nile Virus in San Mateo County in 2016

Burlingame, CA – July 7, 2016

Two dead American crows, one collected from Atherton and another collected from Redwood City, tested positive for West Nile virus (WNV) on July 6th. This is the first indication of the presence of WNV in San Mateo County in 2016.

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West Nile Virus Year-to-Date Comparison 2014/2015
As of Nov. 4, 2015

This table compares the number of bird and mosquito samples testing positive for West Nile virus this year compared with this time last year.

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West Nile Virus Surveillance Update
Updated Oct. 7, 2015

In 2015 to date, 16 dead birds and five mosquito samples have tested positive for West Nile Virus. No sentinel chickens or humans have tested positive for West Nile virus in San Mateo County this year.

In 2014, 20 dead birds and 15 mosquito samples in San Mateo County tested positive for West Nile virus. No sentinel chickens or humans tested positive in 2014.

For the latest statistics on West Nile virus in California, visit the California Department of Public Health’s West Nile virus website.

Sept. 2015 West Nile virus risk assessment

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West Nile Virus Year-to-Date Comparison 2014/2015
As of Oct. 1, 2015

2014-2015 Year-to-Date MIR (minimum infection rate) Comparison

This table compares the MIR (minimum infection rate) of mosquito samples collected in San Mateo County in 2014 and 2015, This number is a measure of what proportion of our mosquito population (per 1000) is carrying West Nile virus.

 

2014-2015 Year-to-Date Positive Bird and Mosquito Sample Comparison

This table compares the number of bird and mosquito samples testing positive for West Nile virus this year compared with this time last year.

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