Delaware public health officials have confirmed the state's first human case of West Nile virus this year.
Officials said Friday that a woman in her early 20s living in New Castle County tested positive for the virus on Wednesday.
For the past five years, the state usually has reported no more than one case per year, but there were nine reported cases of West Nile infection last year.
The virus is transmitted by mosquitoes, but officials say roughly 80 percent of people infected with West Nile virus will not become ill.
The federal Centers for Disease Control estimates that only 20 percent of those infected will develop West Nile fever, with mild symptoms including fever, headache, body aches, a skin rash on the chest or back and swollen lymph glands.