SAN DIEGO -- California health officials have confirmed 16 cases of swine flu statewide, an increase of two from the previous day.

Also Thursday, the state Department of Public Health said it was investigating 23 probable cases of the virus.

The confirmed cases are in five counties: seven in San Diego County, five in Imperial County, two in Marin County and one each in Sacramento and San Bernardino counties.

San Diego has the highest number of probable cases, with eight, followed by Riverside and Santa Clara counties, with four each. Sacramento County has three probable cases, while Los Angeles, San Bernardino, San Joaquin and Tulare counties have one each.

Gov. Arnold Schwarzenegger said 29 counties had asked for antiviral medication. California also has sent additional health workers to San Diego and Imperial counties.