There are about 2,000 people living with HIV in Sonoma County, according to county estimates, and 500 of those infected people do not know they have the virus, according to the local public health division.

They are the primary target group that local HIV/AIDS advocates are trying to reach this week with expanded HIV testing opportunities that kick off local efforts tied to National HIV/AIDS Testing Day Monday.

"About a quarter of them don't know they have HIV," said Rick Dean, executive director of Face to Face, which provides support for people with AIDS.

The numbers are a projection based on the number of people known to have HIV and the area's population.

Both Face to Face and Drug Abuse Alternatives Center, or DAAC, are expanding their testing days and hours this week. The Face to Face office is located at 873 Second Street, Santa Rosa and DAAC is located at 2403 Professional Drive, Santa Rosa.

The test being given at both location is the oral swab test, which produces results in about 20 minutes. Dean said that at Face to Face, staff will also provide risk-reduction counseling.

"People can have their questions answered about what's more riskier than something else," he said.

Although the focus is on those who engage in unsafe sex, the federal Centers for Disease Control and Prevention, or CDC, recommends that all adults and adolescents receive routine screening for HIV. Those at high risk should be tested annually.

Sonoma County provides some funding for drug center testing through a contract for services, said Mark Netherda, the county's interim public health officer.

Netherda said the large number of people who are unaware they are carrying the virus is "one of the forces driving the CDC's recent recommendation for increased testing."

Dean said that increased testing is one of the best forms of prevention against the progression of AIDS. He said most people on a regimen of antiretroviral medications have a much smaller load of virus in their blood, which reduces the risk of transmission.

Discovering whether or not you have contracted the virus and early treatment is crucial to living healthier and having a better medical outcome, health officials said.

"Knowing your status you can deal with it," Dean said. "What you don't want it to do is allow it to go unchecked which wreaks havoc on your immune system."

A donation of $15 will be requested for the test, though no one will be turned away for inability to pay.