Boulder County government offices are closed Wednesday, June 19, in observance of Juneteenth. Primary Elections Vote Center locations are open.

News Archive
ATTENTION: This news article is more than 1 year old and information may be outdated.

July 12, 2022

Mosquito Traps in Boulder County Test Positive for West Nile Virus

Boulder County, Colo. – Boulder County Public Health (BCPH) has confirmed that mosquito traps in unincorporated Boulder County, Longmont, Erie and Superior tested positive for West Nile virus (WNV).

WNV is transmitted to humans when an infected mosquito bites them. While most infections are mild, severe infections can cause encephalitis (inflammation of the brain) and/or meningitis (inflammation of the brain’s lining), loss of vision, paralysis, coma, tremors, convulsions and death.

Symptoms of WNV can include fever, extreme fatigue, headache, body aches, skin rashes and swollen lymph nodes, and generally appear three to 14 days after infection. Anyone experiencing these symptoms should consult their health care provider.

“Longer days and summer weather lead to more people outside when mosquitos are most active, at dawn and dusk. Recent high temperatures and standing water create an ideal environment for mosquitos to breed,” said Marshall Lipps, Boulder County Public Health Environmental Health Specialist. “There is no treatment, cure or human vaccination for WNV, and health care providers can only treat symptoms to help patients feel better and possibly recover more quickly. Everyone should protect themselves and their loved ones by understanding their risks and taking proactive steps to keep everyone safe.”

BCPH urges residents to follow the 4Ds:

  1. Use DEET-enhanced insect repellent or alternatives, including Bite Blocker, Picaridin, Oil of Lemon Eucalyptus, or IR3535.
  2. DRESS in long sleeves and pants.
  3. Avoid the outdoors from DUSK until DAWN.
  4. DRAIN standing water outside your home.

Mosquito season typically lasts from late April until mid-October and ends with the first freeze in the fall.

The vector index is calculated using the total number of mosquitoes in a trap area and the proportion infected with WNV. Emergency spraying may be recommended when the vector index reaches 0.75 or higher. A list of scheduled mosquito spraying is available at

The Colorado Department of Public Health and Environment provides up-to-date data at

For more information about WNV, mosquito activity in Boulder County, or steps you can take to protect yourself and your loved ones, visit