Public health officials this week confirmed the first West Nile virus infection so far this year in Riverside County.

Eric Frykman, the county's public health officer, said this week that the first person to be infected by the virus is a 36-year-old Riverside-area resident, who is recovering at home following hospitalization. Frykman said local health officials have not determined how the person contracted the virus.

Discovered in Africa more than a half-century ago, the virus spread by mosquitos showed up in the United States along the East Coast in 1999 and it has spread to 47 states since then. It is established throughout California.

Consequently, health officials urge area residents to take precautions, such as avoiding going outdoors at dawn and dusk when mosquitoes are most active, applying insect repellent and replacing damaged window screens.

For most people, exposure is of little concern. Health officials say about eight in 10 people aren't affected and most of the rest develop mild symptoms such as headache and fever. But an infection can be fatal.

So far, 164 infections have been confirmed statewide, according to the California Department of Public Health. That compares to the 138 cases that had been recorded by this time last year. Ten people have died across the state as a result of the virus this year, more than the seven deaths reported for all of last year.