US porn industry halts filming after another performer contracts HIV. (Reuters)
A California porn actor contracts HIV on setReuters

A porn actor in California has contracted HIV from a co-star, while shooting an adult film.

Health officials issued an alert after the man tested positive for the virus, but is yet to release any further details about the investigation.

The Department of Public Health said it has "very strong evidence" that a male porn star contracted HIV after having unprotected sex during an out-of-state film shoot.

He then went on to have unprotected sex with several other male actors during two subsequent film shoots.

Before the first shoot, he had tested negative for HIV. However, during the second shoot he had symptoms of a viral infection, the alert said.

"The actor went to a clinic and had another blood test that showed he had recently become infected with HIV."

Since then, an actor on the second shoot has tested positive for HIV. "Public health investigation and laboratory results provide very strong evidence that the actor transmitted HIV to the other actor as a result of unprotected sex during the film shoot," the statement said.

"Public health investigation and laboratory results provide very strong evidence that the actor transmitted HIV to the other actor as a result of unprotected sex during the film shoot," the statement said.

"The actor thought that he was 'negative' for HIV at the time of the two film shoots, but in fact he was infected and probably transmitted HIV to another actor. Some adult entertainment film companies require actors to have a negative HIV test within two weeks prior to a film shoot.

"However, very early in an HIV infection the test can be negative, even though the actor really does have HIV. In this case, the actor and production company thought he was HIV-negative during filming. Shortly after his negative test, HIV levels in his body rose rapidly to where he could infect other actors through unprotected sex."

Michael Weinstein, president of the Los Angeles-based Aids Healthcare Foundation, said the case shows that condoms should be mandatory for porn actors.

Since 2012, performers in adult films shot in the county of Los Angeles are required to wear condoms. Industry officials have claimed this has led to adult films being made outside the county. In August

In August 2014, a similar law which would have required performs in adult films shot anywhere in California to use condoms died without debate in the state's Senate Appropriations Committee.

HIV tests can show false negative results, up to six months after a person is infected.