First human case of West Nile virus reported; take precautions to avoid bites

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Deanna Herbert, Communications Specialist | 303-692-2702 |



DENVER: The Colorado Department of Public Health and Environment is reporting the first human case of West Nile virus in Colorado this year. The case, reported to CDPHE on Aug. 12, presented in a person who resides in Delta County.  West Nile virus is most commonly spread to people by the bite of an infected mosquito.


Weekly mosquito testing for West Nile virus began statewide in June. Counties or municipalities trap adult mosquitoes, and labs test them,  providing an estimate of the number that are infected. The results help pinpoint the risk to humans in the area. This year, West Nile virus-positive mosquitoes have been found in Larimer, Delta, and Weld counties.  Not all counties and municipalities test mosquitoes, so it’s important for all Coloradans to take steps to protect themselves throughout the summer.

“When the virus is present, people are at risk, but there are simple precautions people can take to protect themselves,” said Jennifer House, state public health veterinarian. “Use an effective insect repellent, wear protective clothing, or stay indoors when mosquitoes are active, and mosquito-proof your home.” 


Most human West Nile virus cases are reported in August and September. In 2019, Colorado had 122 reported human cases of West Nile virus, including eight deaths.


Most people infected with West Nile virus don’t have symptoms. About 20% of infected people will have flu-like symptoms, and fewer than 1% develop a serious, potentially deadly illness. People over age 60 and those with certain medical conditions are at greater risk of serious illness. See a health care provider if you develop severe headaches or confusion.


To protect yourself:

  • Use insect repellents when you go outdoors. Repellents containing DEET, picaridin, IR3535, and some oil of lemon eucalyptus, and para-menthane-diol products provide the best protection. Follow label instructions.
  • Limit outdoor activities at dusk and dawn, when mosquitoes that carry West Nile virus are most active.
  • Wear protective clothing (long pants, long-sleeved shirts, and socks) in areas where mosquitoes are active. Spray clothes with insect repellent for extra protection.    

To mosquito-proof your home:

  • Drain standing water around your house often. Empty water from tires, cans, flowerpots, clogged gutters, rain barrels, birdbaths, toys, and puddles.
  • Install or repair screens on windows and doors.

For more information, visit the department’s West Nile virus web page