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August 17, 2020

Mosquito Traps in Superior, Louisville, and Longmont Test Positive for West Nile Virus

Boulder County, CO - Boulder County Public Health has confirmed that mosquitoes in Superior, Louisville, and Longmont have tested positive for West Nile virus (WNV). The positive mosquito pools came from traps near Coal Creek Golf Course and Coal Creek Trail in Louisville, Original Town in Superior, and Isaak Walton Park and St. Vrain Greenway in Longmont.

The vector index, which describes the relative risk of West Nile virus transmission, is 0.21 for Zone 3 (Superior and Louisville combined) and 0.20 for Zone 2 (Longmont). The vector index is calculated based on the total number of mosquitoes present in a trap area and the proportion of which are infected with WNV. Emergency spraying may be recommended when the vector index reaches 0.75 or higher.

WNV is transmitted to humans from the bite of an infected mosquito. While most infections are mild, the more serious 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 include fever, extreme fatigue, headache, body aches, and can also include skin rashes and swollen lymph nodes. Generally, symptoms appear 3-14 days after being bitten by an infected mosquito. Anyone who experiences these symptoms should consult their health care provider.

There is no treatment, cure, or human vaccination for the virus. Health care providers can only treat the symptoms to help patients feel better and possibly recover more quickly.

“Even though it can be inconvenient, taking steps to protect ourselves and loved ones is the best thing we can all do to prevent becoming very ill,” said Marshall Lipps, Boulder County Public Health environmental health specialist. “Our recent high temperatures and standing water have created the ideal environment for mosquitos to breed.”

Boulder County Public Health officials urge 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 generally lasts from late April until mid-October. The season typically ends with the first freeze in the fall. No Boulder County residents have tested positive for West Nile virus this season. State data is available at:

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