The Centers for Disease Control and Prevention in Atlanta said Friday it received reports of 5,674 cases of West Nile virus -- the highest number since 2003.
More than half of the West Nile neuroinvasive disease cases were reported from just four states: Texas, California, Illinois and Louisiana.
Of all West Nile virus cases, 51 percent were neuroinvasive cases -- capable of entering or infecting the central nervous system.
West Nile viruses cases peaked in late August, with 92 percent of cases having illness onset during July-September. The median age of the patients was age 56, 56 percent were male, 62 percent were hospitalized and 286 died. The median age of those who died was age 77.
Officials said West Nile may be the best known arboviruses, but viruses transmitted via mosquitoes and ticks also include meningitis and encephalitis.
The findings were published in the CDC's Morbidity and Mortality Weekly Report.