Arizona experienced the nation's worst outbreak of West Nile virus during this year's season, accounting for nearly one in five severe cases in the nation, a new report shows.
A total of 159 confirmed cases were reported in Arizona this year through Nov. 30, according to the Centers for Disease Control in Atlanta. At least a dozen Arizonans died. State officials updated the count on Dec. 2, reporting 163 cases.
Arizona had nearly 20 percent of the nation's neuroinvasive-disease cases. The disease attacks the nervous system and can lead to life-threatening West Nile encephalitis and West Nile meningitis, the CDC reported.
New York, with a total of 127 cases, was the only other state to have more than 100 reported West Nile cases so far this year.
The spike in Arizona was so severe that CDC officials visited in September to study the outbreak. It was primarily concentrated in the southeast Valley municipalities of Gilbert, Chandler and Tempe, as well as in Pinal County.
The CDC studies took blood samples from birds, which carry the virus, and mosquitoes, which transmit it to humans through bites, and studied human cases. The CDC is still analyzing the data.
"The goal is to try to have some conclusions made and lessons learned before the 2011 (West Nile) season," said Craig Levy, a manager for the Arizona Department of Health Services' vector-borne disease program.
Scientists were surprised to see Arizona's urban desert region lead the nation in cases, considering West Nile was thought to be more prevalent in mosquito-rich environments, he said.
Levy hoped that studying the outbreak would lead to a better understanding of the disease, which was first found in Arizona in 2004. That year, there were 391 reported cases and 16 deaths.
West Nile first appeared in North America in 1999, and spread to the U.S., spiking in humans in 2002 and 2003.
Since then, the federal government and each state have adopted prevention programs. Those programs include public-awareness campaigns about the importance of using insect repellent and removing stagnant water where mosquitoes breed, as well as fogging larger regions.
Marc Fischer, an epidemiologist with the CDC's division of vector-borne diseases, said that the fight against West Nile since it spiked globally has frustrated scientists.
"We've learned how to identify it and can intervene, make physicians aware, but still don't know how to prevent it," he said. "We use the real-time data to find out in the longer term how we can better identify and predict the places where these outbreaks are going to happen so we can intervene before an outbreak."
The virus's latest victim was Cecilia Esquer, a native Arizonan and longtime Tempe Latina civil-rights activist.
Esquer, 68, died last week of encephalitis after contracting West Nile in October.
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