Health officials have identified four human cases of West Nile infection in Weld County. The infected people range from 15 to 81 years of age.

Three cases involve West Nile fever; the fourth is West Nile neuroinvasive disease. West Nile neuroinvasive disease is the most serious type of infection, affecting the brain and spinal cord. The majority of people who contract West Nile will show no symptoms.

"The number is probably going to go up in the next few days," said Eric Aakko, spokesman for the county's health department. There are more cases in the county that haven't been confirmed yet,

36 people have been infected with West Nile so far in Colorado.