The actor was a patient of the Adult Industry Medical Healthcare Foundation, a San Fernando Valley clinic that caters to actors in the multibillion-dollar adult entertainment industry. The actor's identity and gender have not been released.
Clinic spokeswoman Jennifer Miller told the Los Angeles Times that efforts are under way to notify individuals who may have had sexual contact with the actor. Miller did not return calls or e-mail from The Associated Press on Tuesday.
Wicked Pictures and Vivid Entertainment told the Times that they stopped production as a precaution when the positive test was revealed.
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 for contracting HIV and other diseases. Major adult film producers, including Hustler's Larry Flynt, have spoken out against the use of condoms in porn because viewers find them to be a turnoff.
Last year, a woman tested positive for HIV immediately 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.
Porn actors are required by law to test negative for HIV and other sexually transmitted diseases within 30 days of going to work on a film.
State workplace safety officials at Cal/OSHA are considering strengthening rules designed to prevent transmission of disease through bodily fluids to specify the use of condoms in the adult entertainment industry.
Currently, the same laws that call on health care professionals to wear gloves and other protective barriers when dealing with patients applies to the adult film business, but the laws don't make specific provisions for porn.
AIDS Healthcare Foundation President Michael Weinstein said his organization has been advocating for a tightening of the rules, and the adult entertainment industry and AIM clinic would "do everything in its power to prevent us from knowing who was impacted."
Weinstein said the latest case is the ninth HIV-positive adult film star to be treated at the AIM clinic since the 2004 outbreak.
Chief Counsel for Cal/OSHA Amy Martin said the clinic has been uncooperative in providing state regulators with key information by citing a patient's federal right to medical privacy.
But the clinic has even refused to provide redacted copies of employment histories for infected actors, which would allow the state to investigate porn production companies without naming the sick patients, Martin said.
HIV is spread most often through sexual contact, but can also be contracted through sharing contaminated needles for drug use, infected blood products, or babies born to or breast-fed by infected women. It is the cause of AIDS, an immune disease that gradually destroys the body's ability to fight illness.