News Release

Number of West Nile human cases continues to climb

Department: Health & Environment
Release Date: Aug 20, 2013


Jane Viste

As of Monday, August 19, thirty persons have been confirmed to have West Nile virus (WNV) in Larimer County, eight of those having the most serious “neuroinvasive” form which includes meningitis, encephalitis, and paralysis.  For every neuroinvasive case, it is estimated that 150-250 people have been infected, and 40-60 have become ill.


Two additional West Nile infections were identified in Fort Collins blood donors who appear to be healthy so far.  Screening blood for WNV catches most—but  not all—infected blood donations, and those units are discarded.  A Coloradan died in 2012 from a blood donation that was infected with West Nile Virus.


“We expect the number of human cases to continue rise over the next few weeks despite the recent spraying,” said Dr. Adrienne LeBailly, director of the Health Department.  “We believe all the reported illnesses so far have occurred in individuals who were bitten in July, when the number of infected Culex mosquito was beginning to rise rapidly.  These cases are only being reported to public health now.  People infected in August will be reported to us in the coming weeks and months.” 


In addition to human cases, eight raptors that were brought to the Rocky Mountain Raptor Program in July have been confirmed to have died from West Nile virus, and additional raptors have WNV tests pending.  All but two have died. 


West Nile virus is a disease carried by infected Culex mosquitoes that can cause mild to severe illness.  About 75% of people who are infected  are asymptomatic; about 25% will develop West Nile Fever.  Less than 1% develop the most severe neuroinvasive from, which can lead to hospitalization, critical illness, chronic disability or even death. 


West Nile virus was first diagnosed in Larimer County residents in 2003 when over 500 cases of the illness were reported, and 9 county residents died.  According to LeBailly, “At this time, 2013 looks like it will be the worst West Nile outbreak in Larimer County since 2003. Of the cases reported so far, eight of those have had the neuroinvasive form. It’s very important for people to understand that West Nile virus can cause devastating illness, chronic disability and even death in some people. But it also can be prevented though community and individual actions.”


To protect yourself from mosquito bites, the Health Department recommends the following:



For more tips on what you can do to prevent West Nile virus, or on repellent use, visit: or call 498-6700.