LOS ANGELES - At least five companies in California's multibillion-dollar adult entertainment industry have halted production after an actor tested positive for HIV, and more shutdowns were possible, the head of a major production company said Wednesday.

The actor's identity and gender have not been released by the Adult Industry Medical Healthcare Foundation, the clinic where the case was discovered. The clinic was working to identify and test on-screen partners of the actor.

Vivid Entertainment Group and Wicked Pictures announced production halts Tuesday as a precaution.

Vivid founder Steven Hirsch would not name the other companies that have shut down but said more might follow.

"From Vivid's perspective, there was no question that when we heard this, we immediately shut down production and said let's get the facts and evaluate them before we move forward," he said. "Adult entertainment companies act responsibly, and no one wants to see another person test positive if there's anything they can do to stop it."

Jennifer Miller, a spokeswoman for the Adult Industry Medical Healthcare Foundation, did not return calls or an email from The Associated Press seeking further comment.

Los Angeles County public health officials and state occupational health officials have said the widespread lack of condom use on porn sets puts performers at risk of contracting HIV and other diseases. Adult film producers say viewers find condoms to be a turnoff.

Last year, a woman tested positive for HIV after making an adult film, and in 2004 an HIV outbreak affecting several actors spread panic in the industry and briefly shut down productions at several California studios.

In recent years, advocates and health officials have tussled with porn producers and free speech advocates over the use of condoms in adult films.

State workplace safety officials at Cal/OSHA are considering strengthening rules designed to prevent transmission of disease by requiring the use of condoms in the adult entertainment industry.

HIV is spread most often through sexual contact but can also be contracted through sharing contaminated needles for drug use, infected blood products, or by babies born to or breast-fed by infected women.

HIV is the cause of AIDS, an immune disease that gradually destroys the body's ability to fight illness.

In an average month, Vivid spends $250,000 to shoot four movies, which require a total of 12 to 15 days of shooting, Hirsch said.

The company currently has a stockpile of unreleased movies, and it would take months without any new production activity to affect Vivid's release schedule, he added.

Mark Kernes, senior editor at Adult Video News, said he expects most production companies to shut down until it's known who had contact with the person known to have HIV.

It's unclear how the industry's bottom line might be affected by halted production because many companies such as Vivid could sustain sales with backlogs of unreleased titles, Kernes said.

Like other entertainment industries, adult film makers have been hurt by the recession and the Internet, where pirating and free downloads often cut producers out of a profits.

Last year, in a tongue-in-cheek complaint about the sour economy, Hustler magazine publisher Larry Flynt and Girls Gone Wild chief executive Joe Francis called for a $5 billion federal bailout. They said adult DVD sales and rentals decreased 22 per cent.