Arizona continues to lead the nation in people infected with the West Nile virus with 57 cases reported so far, including the first this year outside Maricopa County, state health officials said Thursday.
Eight other states have reported human cases, according to the Centers for Disease Control and Prevention. California has the next highest number of human cases with 11.
There have been 19 new human West Nile cases in Arizona in the past week, including a Pinal County teenager. That raises the number of cases in Arizona this year to 57, all but one in Maricopa County.
A 74-year-old north Phoenix woman died of the mosquito-borne disease last week. Those infected have ranged in age from 3 months old to 87 years old.
Health officials are concerned the number of human cases could grow with upcoming July 4 outdoor activities.
"As this latest report shows, West Nile virus can affect all Arizonans, including the very young," said Arizona Department of Health Services Director Catherine Eden. "This is a totally preventable disease."
Health officials have warned people to get rid of standing water and other mosquito-breeding sites. They have also recommended the use of repellents that contain the chemical DEET.
Last year, Arizona saw its first case of West Nile. Fifteen cases were reported and one person died.
The virus is normally transmitted to humans and animals by mosquitos, which become infected when they feed on infected birds.
About 80 percent of people who are infected with the virus show no symptoms while 20 percent could develop symptoms such as fever, nausea, headache and muscle aches, health officials said. In rare cases, West Nile progresses to life-threatening encephalitis or meningitis.