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Public Health - News

Posted on: August 7, 2023

JCPH Reports First Human Case of West Nile Virus in Jefferson County

Jefferson County Public Health logo

Jefferson County, CO — The Colorado Department of Public Health and Environment (CDPHE) has reported the first human case of West Nile Virus (WNV) in Jefferson County. Additionally, WNV has been found in mosquitoes in at least seven counties throughout Colorado this season. Mosquito populations are at historic levels in some parts of the state due to the high rainfall this year. This unusually high mosquito activity along with known presence of the virus in Colorado and Jefferson County has caused an elevated risk of WNV transmission to humans.

The best way to prevent WNV is to avoid being bitten by mosquitoes. Residents should also eliminate standing, stagnant water where mosquitoes breed. Even quick trips outside allows time for an infected mosquito to bite. Everyone should take precautions to avoid mosquito bites.

Protect yourself, your family and your community from mosquito bites and WNV by sticking with the four Ds: Drain, Dusk/Dawn, Dress and DEET.

  • Use DEET or an alternative.

    • If using DEET, choose the concentration that best fits the amount of time spent outside. For example, 25 percent DEET lasts up to 5 hours and 5 percent lasts 45-90 minutes. Use a concentration of 30 percent or less for children. Children under 6 months should not use DEET. 

  • Dress in long sleeves and pants.

  • Avoid outdoor activities between dusk and dawn.

  • Drain standing water.

West Nile Virus can be debilitating and life-threatening. The incubation period for WNV disease is typically 2 to 6 days, but ranges from 2 to 14 days and can be several weeks in people with immunocompromising conditions. 

In 2022, Colorado reported 206 human cases of WNV, including 20 deaths due to the virus. People aged 60 years and older and those with certain medical conditions are at greater risk of serious illness. Talk with a health care provider if you develop severe headaches or begin experiencing confusion.

To learn more about WNV, go to the JCPH website or the CDPHE WNV page.

About Jefferson County Public Health 

Public health is what we do collectively to prevent illness and premature death and promote health in our neighborhoods and communities. Jefferson County Public Health (JCPH) is a nationally accredited health department committed to promoting and protecting health across the lifespan for all people through prevention, education and partnerships. To learn more about JCPH visit You can also follow JCPH on Twitter @JeffcoPH [external link], Instagram @JeffcoPH [external link] and Facebook @jeffcopublichealth [external link].

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