No cases of West Nile have been reported in people yet for 2018.
The Weld County Department of Public Health and Environment says it is the first human case of the virus this year in Colorado.
The virus is transmitted to humans through mosquitoes, which acquire the virus by feeding on infected birds.
"Mosquitoes are weak flyers and won't travel far from where they are born - if there are mosquitoes in your backyard or neighborhood, they are likely laying eggs there as well", said Matt Helwig, a biolgist with the DEP mosquito program.
The case comes amid what the health department called a "surge" in mosquitoes infected with the virus across the county.
The number of confirmed infections can vary from year to year. Tests results confirmed West Nile Virus Thursday.
In Maryland, there were five reported cases of West Nile previous year, according to the Centers for Disease Control and Prevention. Symptoms usually develop between two and 15 days after a person has been bitten and can include fever, headache, nausea, vomiting, body aches, skin rash and swollen lymph glands.
Benjamin Schwartz, director of epidemiology and population health for Fairfax County, said that with the high levels [of the virus] in mosquitoes and the recent rains leading to even more mosquitoes, it is important for residents to take precautions for themselves and their families.
Residents can also eliminate habitat by getting rid of standing and stagnant water where mosquitoes lay eggs.
Those most at risk for serious complications are people older than 50 and people with suppressed immune systems.