Human Cases of West Nile Confirmed in Utah

(Salt Lake City, UT) – At least 11 Utah residents in Salt Lake, Davis, and Weber counties have been diagnosed with West Nile virus (WNV) this season, (nine neuroinvasive, and two non-neuroinvasive), one death has occured in the Weber/Morgan Health district, and five additional cases are pending confirmation.  While most people infected with West Nile virus don’t develop any symptoms, about one in 150 people develop a severe illness that affects the central nervous system. Among patients with neuroinvasive disease about one in 10 die.

According to Hannah Rettler, Utah Department of Health (UDOH) Vectorborne/Zoonotic Epidemiologist, “Utah is now seeing the highest number of mosquito trap sites test positive for WNV than we’ve had in the history of West Nile surveillance in the state. As of August 23, 2021, 8% of mosquito trap sites tested positive for WNV (506 out of 5,906 total sites). For reference, in 2020, 0.008% tested positive and in 2017, the year with the highest number of human WNV cases (62), 8% of mosquito trap sites tested positive for WNV.

“West Nile virus is an annual presence in Utah and it isn’t going away,” adds Rettler. In addition to the human cases, nine horses have tested positive for West Nile virus, two crows, two sentinel chickens, one magpie, one scrubjay, and one red-tailed hawk. Rettler worries, “We could see many more Utahns become ill unless residents take steps to reduce mosquito exposure.” Utah records an average of 12 human cases of West Nile virus each year, ranging between two and 21 cases. In 2019, there were 21 human cases, and in 2020 there were two.

Taking these simple precautions to avoid mosquito bites is the best way to reduce your risk for infection.

  • Wear long-sleeves, long pants, and socks while outdoors and use an insect repellent with 20%-30% DEET, which is safe to use during pregnancy. Repellents are not recommended for children younger than two months of age.
  • The hours from dusk to dawn are peak biting times for many mosquitoes. Consider rescheduling outdoor activities that occur during evening or early morning.
  • Mosquitoes lay their eggs in standing water. Remove any puddles of water or standing water including in pet dishes, flower pots, wading and swimming pools, buckets, tarps, and tires.
  • Report bodies of stagnant water to your local Mosquito Abatement District (MAD). Visit for a list of MADs.
  • Keep doors, windows, and screens in good condition and make sure they fit tightly.
  • Consult with an immunization travel clinic before traveling to areas that may have mosquito-borne illness such as Zika or dengue and take the necessary precautions.

West Nile virus is usually transmitted to humans through the bite of an infected mosquito, but not all mosquitoes carry the virus. Symptoms of the severe form of West Nile virus include high fever, severe headache and stiff neck, disorientation, and confusion. If you are experiencing symptoms, contact your healthcare provider immediately.

West Nile virus surveillance will continue into early fall. You can find an updated weekly West Nile Report on the Utah Department of Health’s website here:  For more information about West Nile Virus, call your local health department or visit

Media Contact:

Charla Haley

 (c): 801-230-5927