California health authorities confirmed the first case of influenza A/H1N1 at a state prison on Sunday, indicating the continuing spread of the virus.

As a result, visiting hours and other activities at the Centinela State Prison, some 130 miles (about 200 km) southeast of Los Angeles, have been suspended, the state Department of Corrections and Rehabilitation (DCR) said.

The inmate, who is only mildly affected, has been isolated and is getting appropriate medical care, the DCR said in a statement.

The illness was not far from the five other confirmed H1N1 flu cases in Imperial County near the US-Mexican border, according to the statement.

Meanwhile, prison officials affirmed in a news release that they take the outbreak of the flu behind cell doors "very seriously," saying that steps were being taken to reduce exposure danger for both inmates and employees.

Training classes, sessions with volunteers and other communal activities have also been cancelled at the prison.

Also on Sunday, the first three cases of H1N1 infection were confirmed in the Los Angeles area.

According to the Los Angeles County Department of Public Health (LACDPH), the three cases include a female student at the California State University in Long Beach near Los Angeles and two residents in central and southeast Los Angeles.

"These cases do not change our recommendations to the public, but only confirm what we have already suspected -- that this new flu virus is here in L.A. County," said LACDPH director Dr. Jonathan E. Fielding.

"We continue to remind residents that they should not panic. So far, this new flu virus looks and is acting like the regular, seasonal influenza that we already know," he said.

Fielding urged people to be vigilant about personal hygiene, washing hands frequently. Those who believe they are infected should stay home from work or school to prevent spreading the illness.

A total of 26 influenza A/H1N1 cases have been confirmed in California so far.