The immediate threat of mosquitoes infected with West Nile virus found in North Central San Mateo forced health officials to act quickly Thursday night by successfully fogging a concentrated area.

Some residents raised concerns about only having a few hours notice before their homes were sprayed in pesticides, but San Mateo County Mosquito and Vector Control District officials said the threat of a person being infected with the deadly virus warranted a timely response.

“Every night that you know there’s a potential mosquito out there, it’s just another night that someone can contract West Nile virus. So the longer you wait, the more the public is at risk,” said Brian Weber, the district’s assistant manager.

Although birds infected with West Nile are discovered periodically, this was the first time in at least a decade mosquitoes carrying the virus had been found in San Mateo County, Weber said.

Records as far back as 2007 show no human has contracted West Nile in San Mateo County. However, last week, someone from Contra Costa County became the first to test positive in California this year, according to the state’s West Nile website.

After spending about three to four hours fogging the neighborhood between Poplar and Third avenues and El Camino Real and Highway 101, district technicians confirmed Monday they had killed off nearly 77 percent of the mosquito population and the remaining tested clear of the virus, Weber said.

The district discovered the outbreak Thursday and decided to proceed that evening and put out fliers and notices that they would be fogging the area by truck between 11 p.m. and 5 a.m., Weber said.

Cheryl Zuffi, a North Central homeowner who runs a day care business, said she understands the importance of addressing the dangerous mosquitoes, but had concerns about the process.

“It wasn’t what they were doing, it was more that I didn’t feel there was proper notice given and I know we may not have a say in whether they may fog or not, if it’s definitely a situation that they feel is dangerous and they have to do what they have to do, I can understand that. But at the same time, we need more time to be prepared for this because I have a day care and I have pets and I have a lot to be concerned about,” Zuffi said.

The fliers advised residents to bring in any toys or pet bowls left outside, to close windows and doors, diligently wash their hands and thoroughly wash any produce from a resident’s garden.

Zuffi said by the time many homeowners received the notice, it was past the district’s office hours and no one was available to answer questions over the phone. Zuffi said the district should consider different communication platforms or have a notification process in place that would be more effective at reaching everyone and provide a source of answers for concerned residents.

Weber said the district hadn’t fogged since 2006 and this was first time he’s encountered a case of mosquitoes infected with West Nile.

The district used a pesticide called pyrethroid and inspectors returned to different residences and monitored traps to make sure the mosquitoes with West Nile had been killed off, Webber said.

The type of mosquitoes that carry West Nile typically breed in dirty water so people should make sure they don’t let water collect. The inspectors found several homes with dirty stagnant water, including a wheelbarrow that was full, Weber said.

Weber said the district purchased DNA testing equipment about a year ago to perform studies in-house instead of having to send samples to the state and wait for a response. The new equipment proved extremely valuable in finding this recent infestation and then immediately addressing it, Weber said.

“When you’re working in the interests of public health, they’re all kinds of exemptions,” Weber said. “You just have to take the risk of what’s going on and consider that a child or grandmother could get West Nile, which is known to kill people. So in the interest of public health, we thought we should treat as soon as we got the information. That’s why we purchased the DNA equipment, so we could react quickly.”

For more information about the San Mateo County Mosquito and Vector Control District visit

(650) 344-5200 ext. 106

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