Colorado’s first human case of West Nile virus identified for 2023

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STATEWIDE (July 24, 2023) — State health officials confirmed the first human case of West Nile virus in a person from La Plata County this year. Additionally, West Nile virus has been found in mosquitoes in seven counties throughout Colorado this season, including Arapahoe, Boulder, Delta, Denver, Larimer, Pueblo, and Weld. 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 has caused an elevated risk of West Nile virus transmission to humans.

While most people infected with West Nile virus don’t have symptoms, some can develop a serious, potentially deadly illness. In 2022, Colorado had 206 reported human cases of West Nile virus, including 20 deaths. 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.

West Nile virus is most commonly spread to people by the bite of an infected mosquito. To protect yourself:

  • Use insect repellents when you go outdoors. Repellents containing DEET, picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol products provide the best protection. For more information about insect repellents, visit the EPA’s information webpage. Always follow label instructions.
  • Limit outdoor activities at dusk and dawn, when mosquitoes are most active.
  • Wear long pants, long-sleeved shirts, and socks in areas where mosquitoes are active. Spray clothes with insect repellent for extra protection.

In addition to eliminating standing water around your home weekly, you can also mosquito-proof your home by installing or repairing screens on windows and doors.

You can find additional data going back to 2003 on CDPHE’s West Nile virus webpage, which is updated weekly throughout the season.