A Seattle woman tested positive for West Nile virus last month, becoming the first person in King County to acquire the virus locally.
Seattle & King County Public Health announced Monday the woman was most likely infected in late August in the Seattle area, possibly on Bainbridge Island, and was hospitalized in mid-September.
The woman, who is in her 40s, spent one day in the hospital and has since recovered.
Previously all King County cases of West Nile virus occurred in people who had traveled out of Washington state or to Eastern Washington, according to the health department. About six people have been infected annually in Eastern Washington over the last decade.
West Nile virus was detected in a mosquito sample in Pierce County in August, although no human cases have been reported there this year.
The virus has also been detected in horses, birds, mosquitoes, and other mammals in seven Washington counties in 2018, but Pierce County was the first county west of the Cascades where infected animals were found.
Because the virus has been previously detected in Washington state, Dr. Jeff Duchin, a health officer with Seattle & King County Public Health, said the human case in King County was not unexpected.
"King County residents should assume local mosquitos might carry West Nile virus," Duchin said in a statement.
The health department used to do West Nile virus surveillance, but the King County mosquito surveillance program was cut in 2009, and the dead bird surveillance program ended statewide in 2016 due to budget cuts.
About 20 percent of people infected will get sick, and less than 1 percent of people infected will develop severe illness, according to the Washington State Department of Health.
Symptoms of West Nile virus include headache, fever, muscle aches, swollen lymph nodes, and a rash. They can develop up to two weeks after an infected mosquito bites you.
Prevent bite exposure by wearing insect repellant and long-sleeved shirts and pants outside. The health department recommends draining any standing water on your property to prevent mosquito breeding.
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