Last major HIV panic in California's adult film industry was in 2004 when an actor with the virus infected three colleagues

The multibillion-dollar porn industry located in the San Fernando valley of southern California has been thrown into crisis after one of its performers tested positive for HIV.

The discovery was made at the Adult Industry Medical Healthcare Foundation, AIM, a clinic that carries out mandatory testing for about 1,200 porn actors in the valley every month. The clinic has refused to reveal the gender of the performer or which studio he or she worked for, but it has started to track down all other actors known to have been exposed and is now quarantining them until they can also be tested.

Two major studios have temporarily suspended filming, Vivid Entertainment, which is probably the largest porn-production company in the world, and Wicked Pictures.

The anonymous performer is the first to have tested positive for HIV in over a year. The last major panic to grip the valley was in 2004 when a male star, Darren James, was found to have contracted the virus, probably from a filming session in Brazil.

He in turn infected three actresses. More than 30 studios shut down temporarily while tests on many other performers who had engaged in filming with the four infected individuals were tested.

The new positive test result has thrown up the long-debated issue about condoms in the porn industry. In the wake of the 2004 scare condom use became prevalent in the valley, but gradually filming without protection returned to being the norm as studios argued that the use of condoms was driving down sales.

James, the actor at the centre of the 2004 events, told the Los Angeles Times that he was dismayed by the lack of progress on the issue in the past six years. "The actors … they're not getting the protection that they need. There should have been mandatory condoms," James said. "I knew it was going to happen. And how many years has it been? Again. They went right back to the same habits. Good grief, it's like my deal, all over again. I hate that."

The San Fernando valley has become the focal point of the porn industry since the 1970s. It has been dubbed the San Pornando valley and Silicone Valley, a play on the prevalence on artificially enhanced breasts.

Wicked Pictures is one of the only major studios that requires actors to wear condoms. It said in a statement: "Even though Wicked Pictures is condoms-mandatory, we have postponed our upcoming productions to give AIM a chance to create a comprehensive quarantine list.

"Thanks to the continued efforts of AIM the entire industry was all made aware of this possible threat on the same day."

AIM was set up by a leading actor in S&M films, Sharon Mitchell, who appeared in more than 2,000 films and directed several before retiring and turning her energies to the health side of the business. The clinic has been in an ongoing tussle with local health and safety bodies that argue that testing for HIV is not enough and that protection must be given a higher priority.

The clinic has also faced legal suits attempting to force it to reveal the numbers and identities of infected actors. So far it has managed to resist the challenges.

Under California law employers must safeguard their workers against the exchange of bodily fluids. However, most studios bypass the requirement on the grounds that the actors they use are self-employed.

The question of condom use is now likely to move to centre stage later this month when a panel that advises the state's health authorities meets to discuss porn industry rules.